Climate Change and Wetlands

9. The findings of this paper are relevant also to implementation of a number of Resolutions being considered for adoption by COP8, including inter alia COP8 - DR 4 on wetlands and Integrated Coastal Zone Management, COP8 - DR 5 on partnerships and synergies with Multilateral Environmental Agreements and other institutions, and COP8 - DR 17 which provide guidelines for global action on peatlands.

1.2 Scope and sources of information

10. The focus of this paper is the impacts of climate change on wetlands, and adaptation and mitigation options. To set the context for this, the paper also provides a brief overview of the importance and global distribution of wetlands, as well as of recent and projected changes in global and regional climate and some other pressures (e.g., land use and land cover change). The paper also examines adaptive management options and reviews the extent to which the tools and guidelines contained in the Ramsar 'toolkit' of Wise Use Handbooks provides adequate guidance in support of management responses to climate change for wetlands. Climate change projections have a number of associated uncertainties due to the current state of knowledge and the complexity of the problem. These issues are addressed in the final section of the report in relation to how the uncertainties affect the robustness of projections of climate change and its impacts on wetlands.

11. It is beyond the current scope to address in detail the multiple pressures of global change and their overall impacts, and there is a need to examine further the effects of the multiple pressures on wetlands, which may be more important than the effects of climate change alone. Furthermore, as reflected in this paper, available information on adaptation and mitigation options for wetlands is limited, and more detailed regional or local work on this issue should be a priority for the future.

12. The major sources for information on climate change impacts on wetlands and adaptation and mitigation options were the results of the recent Intergovernmental Panel on Climate Change (IPCC) assessment reports (e.g., IPCC 1998, 2000, 2001a, 2001b, 2001c). These have been supplemented with more recent work on wetlands and climate change published since 2000. The section on adaptive management and vulnerability assessment draws on material from Kay & Waterman (1993), Harvey et al (1999), and van Dam et al (1999). Information on the global extent and distribution of wetlands is drawn from Finlayson & Spiers (1999) and Finlayson et al (1999).

2. The importance of wetlands and their values and functions

13. Wetlands are valuable resources that supply many goods and services (or products, functions and attributes) to people (Finlayson 1996). These goods and services include food, fibre (e.g., reeds), clean water, carbon and other nutrient stores/sinks, flood and storm control, ground water recharge and discharge, pollution control, organic matter or sediment export, routes for animal and plant migration, landscape and waterscape connectivity. Costanza et al. (1997) estimated the total global value of these goods and services provided by coastal areas and inland wetland ecosystems to be US$15.5 trillion or some 46% of the estimated total value of goods and services provided by all ecosystems worldwide.

14. Under the Ramsar Convention, ecological character of a wetland is defined as the sum of the many biological, physical, and chemical components of the wetland ecosystem, and their interactions (http://www.ramsar.org/key_res_vii.10e.htm). The goods and services provided by an individual wetland are the result of its ecological character and include important wetland functions, such as hydrological and biogeochemical cycling (described further below).

15. Other ecosystem functions are primary and secondary production, animal and plant interaction (e.g., pollination, herbivory), and carrier functions which include connectivity (landscape and waterscape), routes for animal migration, plant dispersal (including seeds), maintenance of biodiversity and aesthetic, spiritual, cultural and recreational services.

16. Wetland functions, and hence the goods and services provided by wetlands, will be impacted by climate change. For example, wetlands are critically important in global biogeochemical cycling (Sahagian & Melack 1998); but climate change will impact the biogeochemical cycling by affecting the hydrology, net primary production, respiration and decomposition rates and so also carbon and nitrogen cycling in wetlands.

17. Many wetlands contain large stores of carbon, so the release, maintenance or enhancement of these stores under a changing climate will in turn potentially affect future climate change (IPCC 2001c). Maintenance of the ecological character of a wetland (and thus its hydrological, biogeochemical, and ecological functions) will enable people to continue to enjoy the values and benefits derived from the wetland. Hence managing wetlands under climate change can support the delivery of the wise use principles of the Ramsar Convention (Davis 1994) and contribute to sustainable development of wetlands, both locally and further afield.

2.1 Hydrological functions

18. Many wetlands have inherently variable and rapidly reversible "states" driven by sometimes extremely variable water supply. Many of the goods and services provided by wetlands are dependent on their hydrological functions as well as the "state" they are in.

19. Water runoff, water flows, ground water recharge and discharge and flow systems, residence period of the water and turnover time ("flushing of wetlands" and their replenishment) are closely associated with the control of water quality, nutrient cycling, and the distribution and survival of certain plant and animals species (Hollis 1998, Mitsch et al 1994).

20. Many of these hydrological functions operate at the catchment level and thus management of the catchment hydrology will affect the overall functioning of wetlands and the goods and services they provide [(see also Ramsar's guidance on water allocations and management (COP8 - DR 1))].

2.2 Biogeochemical functions

21. Biogeochemical functions of wetlands include the transformation and cycling of elements, the retention and removal of dissolved substances from surface waters, and accumulation of peats and inorganic sediments. These functions retain nutrients and other elements, improve water quality, and affect aquatic and atmospheric chemistry (Sahagian & Melack 1998).

22. Wetlands play an important role in carbon and nitrogen storage, and they are also natural sources of greenhouse gases (GHG) such as methane (CH4) and sulphur dioxide (SO2) (Sahagian & Melack 1998). The general roles played by wetlands in the production, metabolism, storage and release of these compounds (particularly carbon dioxide, methane, nitrous oxide and sulphur dioxide) are briefly outlined below. However, the wide range of wetland types and their differing characteristics in cycling of for different GHGs makes it difficult to identify the specific role of each wetland (Patterson, 1999).

Carbon storage (carbon dioxide and methane)

23. Wetlands are important reservoirs of carbon, representing about 15% of the terrestrial biosphere carbon pools (Bolin & Sukumar 2000; Patterson 1999). When boreal forests and some tropical forested wetlands are included as wetlands, this figure comes to about 37% of the terrestrial carbon pool (Bolin & Sukamar 2000).

24. In terrestrial ecosystems (including wetlands), the majority of carbon is stored in the soil as organic matter, which may be released when the soil is disturbed, for example due to wetland drainage and destruction or fires (Bolin & Sukumar 2000; Gitay et al 2001). In general, carbon in soil is approximately five times higher than that in above-ground vegetation;, but this ratio is much higher in grasslands (~30:1) and wetlands (~15:1) (Bolin & Sukumar 2000). The ability of a wetland to store carbon is related to its hydrology and the associated level of the water table, geomorphology, and local climate (Patterson 1999; Sahagian & Melack 1998).

25. Wetlands and rice fields, when flooded, are among the largest sources of methane from the terrestrial systems to the atmosphere (Cao et al 1998; Dale 1997; Roulet 2000; Sahagian & Melack 1998). Wetland plants enhance methane emissions by acting as conduits of gas exchange, and through the production of root exudates and plant litter. Important factors controlling methane production include rates of primary productivity, salinity, water level, temperature, light, and soil properties (Cao et al 1998; Patterson 1999; Sahagian & Melack 1998). Vegetative biomass, including that of rice, is positively correlated with methane emissions in wetlands, i.e. the larger the biomass the higher the emission of methane.

26. About one quarter of the carbon sequestered by wetlands is subsequently emitted to the atmosphere as methane (Patterson 1999) and approximately one fifth to one third of the global wetland methane emissions are derived from rice paddies (Cao et al 1998). Tropical wetlands appear to be larger contributors of methane to the atmosphere than northern wetlands (north of 45° latitude).

27. As well as being sources of methane, wetlands may also act as sinks of methane although the dynamics of methane storage in relation to primary production and drying/inundation patterns is poorly understood and requires significant further investigation.

Nitrous oxide production

28. Microbiological processes in soils are the major source of atmospheric nitrous oxide (N2O), with fertilizer application and biomass burning probably being the largest anthropogenic sources (Bolin & Sukumar 2000; Watson et al 1992). Emissions from soils are greater under warm and wet conditions, for example in tropical forest environments. There is little information about N2O emissions from wetlands, but peatlands are thought to be neither a significant source or sink (Roulet 2000).

Sulfur production

29. Sulfur gases exist in the atmosphere mostly as sulfate aerosols (i.e., microscopic airborne particles; Carter & La Rovere 2000). Anthropogenic sources of sulfur, particularly sulfur dioxide (SO2) from industrial emissions, are the greatest contributors to atmospheric sulfate aerosols (Watson et al 1992). Sulfur compounds are commonly present in wetlands and are a minor source of atmospheric sulfur. The reduction of sulfate resulting from microbial oxidation of organic materials results in the formation of sulfide gases, including dimethyl sulfide (DMS) and hydrogen sulfide (H2S) (Sahagian & Melack 1998). Fluxes of sulfur gases from coastal wetlands are known to be 10-100 times greater than from the ocean, although their aerial extent is thought to be limited (Sahagian & Melack 1998).

Greenhouse gases

30. The naturally occurring greenhouse gases that exert a positive radiative forcing (i.e., they warm the atmosphere) are considered to be water vapour, CO2, methane, and nitrous oxide. Sulphur dioxide is also considered a greenhouse gas but, in contrast to the others, it has a cooling effect on the atmosphere (Watson et al 1992). Human activity (fossil fuel combustion and land use/land cover change) has affected the concentration of these greenhouse gases in the atmosphere (IPCC 2001a) and this has in turn affected the Earth's climate.

31. Given that a) wetlands store about a third of the terrestrial carbon; and b) the terrestrial biosphere, which at present is a sink, is projected to become a source by the 22nd century, wetlands may become a source for GHGs, either directly due to projected changes in climate or indirectly due to changes in their disturbance regimes.

32. Natural peat-accumulating wetlands (peatlands) are known to be an overall sink for carbon (Gitay et al 2001; Roulet 2000), although CH4 emissions from these ecosystems represent a considerable source of carbon to the atmosphere (Roulet 2000; see below). In a study of the Canadian peatlands, Roulet (2000) estimated that these peatlands are neither a net source or sink of GHGs. However, it was recognised that the calculations carried much uncertainty, due mostly to a lack of knowledge about temporal changes to the peatlands. Existing data on carbon storage in peatlands are highly variable (Gitay et al 2001), and very little is known about the carbon dynamics of non-peat-accumulating wetlands (Roulet 2000).

2.3 Consequences of wetland modification and changes in disturbance regimes

33. Past and present land use and land cover change are the main factors that affect terrestrial sources and sinks of carbon (Bolin & Sukumar 2000; Roulet 2000). Of particular importance is the fact that, during the 1980s, more than 90% of the net release of carbon from land use/land cover change was a result of land use changes in the tropical regions of the world (Bolin & Sukumar 2000).

34. Roulet (2000) identified six anthropogenic modifications that could alter the exchange of gases between wetlands and the atmosphere, in relation to Canadian wetlands: agricultural reclamation; urban and industrial land use; energy development; peat harvesting; forest harvesting; and wetland creation. These modifications are considered also relevant on a global scale, and their consequences are summarised below.

35. In addition, the impacts of climate change on wetlands will also directly and indirectly influence the fluxes of GHGs, either by increasing the respiration rates and primary production and/or by reducing the water table. With increased temperatures this would lead to increased frequency and intensity of fires (Bolin and Sukamar 2000; Gitay et al., 2001). However, while projections for CO2 and CH4 emissions can be made, there is insufficient information to project the fate of N2O emissions under land use change scenarios (Roulet 2000).

Agricultural reclamation

36. Agricultural reclamation includes activities such as drainage, in-filling, construction of dykes, and also cultivation. Lowering of water levels may result in an increase in CO2 emissions but a reduction or even cessation of CH4 emissions. However, CH4 emissions from drainage ditches can be significant (Roulet 2000).

37. Conversion of wetlands to agricultural lands can lead to increases in CO2 emissions, with cropping activities also potentially leading to increases in N2O emissions (Roulet 2000). Of importance here is that agricultural practices often replace diverse natural ecosystems with single species ecosystems, since recent research has shown that ecosystems with high plant diversity were better able to sequester CO2 and nitrogen than ecosystems with reduced biodiversity (Lazaroff 2001a).

38. Agricultural reclamation also results in wetland fragmentation, which can affect other wetland functions such as migration of some animals and plants.

Urban and industrial land use

39. Wetland destruction, through drainage or in-filling, is a common feature of urban and industrial development. The complete removal of a wetland should eliminate the sink for CO2 and the source of CH4 (Roulet 2000). Thus, the overall net effect on GHG emissions could range from negligible to a small increase in emissions (Roulet 2000). Following in-filling and compaction of the wetland soil, some carbon stock will most likely remain part of the soil carbon pool (Roulet 2000).

Energy development and water storage

40. The major modification to wetlands associated with energy development and water storage is the construction of reservoirs and dams. The flooding of former wetlands, and subsequent creation of new wetlands, can result in a number of changes to GHG fluxes.

41. Reservoirs are known to be significant sources of both CO2 and CH4, especially if a former carbon-rich land cover (e.g., forest or peatlands) is inundated. Although the proportion of GHG emissions derived from the former wetland's sediments is usually unknown, it is known that flooding of such systems increases both CO2 and CH4 emissions, and therefore net GHG emissions, significantly (Roulet 2000), and that this can continue over a long period of time.

Peat and forest harvesting

42. Peat harvesting requires the drainage of a peatland, and thus will most likely result in a reduction in CH4 emissions and an increase in CO2 emissions from peat soils. The impact on net GHG emissions could range from negligible to a large increase in emissions (Roulet 2000). In addition, there will be a net loss in the carbon stock due to that contained in the extracted peat.

43. Harvesting of wet forests also involves their drainage, resulting in a reduction in CH4 emissions and a small increase in CO2 loss from the soil. Loss of CO2 is partially offset by carbon uptake in the living biomass of the vegetation, although removal of the tree cover would be expected to minimise this effect. Apart from the impact on the GHG emissions, forestry activities are a threat to the viability of many forested peatlands, but particularly tropical forested wetlands (Gitay et al 2001).

Wetland creation

44. The creation of new, and the restoration of former, wetlands is becoming an increasingly common practice. Wetland creation involves the flooding of soils and the subsequent establishment of aquatic plant communities and formation of organic sediments (Roulet 2000). An increase in net primary productivity (NPP) will lead to the uptake of CO2, while the flooded soils will also contribute to increased CH4 emissions. The overall effect on net GHG emissions is difficult to determine but could range from a small negative effect to a small positive effect (Roulet 2000).

Changes in the frequency and intensity of fires

45. Fires are part of natural dynamics and management regimes of many wetlands. Fire as a disturbance is likely to be affected by climate change, with some regions, for example those experiencing El Niño-like phenomena and those in the higher latitude regions, likely to experience increased intensity and frequency of fires as a result of increased primary productivity and climatic conditions more favourable to fires (Gitay et al. 2001)

Climate change feedbacks

46. Most research on the impacts of climate change on the exchange of GHGs between wetlands and the atmosphere has focused on peatlands (e.g., Anisimov & Fitzharris 2001; Gitay et al 2001; Kundzewicz & Parry 2001; Lal et al 2001). The main points are summarised here, and further information is provided in sections 3 and 4 below:

50. On these figures the area of wetlands worldwide ranges from 7.48-7.78 million km2, but that does not include many other wetland types, such as salt marshes, coastal flats and seagrass meadows, karst and caves, and reservoirs as recognised under the Ramsar Convention.

51. Despite the poor level of overall coverage of national wetland inventory, these estimates are considerably higher than previous estimates for wetland extent, derived largely from remote sensing, which vary from 5.6-9.7 million km2 (Spiers 1999). Darras et al (2000) also report that there are inconsistencies between global wetland datasets, partly due to incompatible classification of data. By combining a number of datasets they provided an estimate of 9.542 million km2 (excluding marine wetlands), but most likely still underestimated the global extent of wetlands, especially the extent of seasonally inundated wetlands.

Table 1. Estimated area of wetlands in each of the regions of the world recognised under the Ramsar Wetlands Convention, from Finlayson & Davidson (1999b); Finlayson et al (1999).

	Estimated area of wetlands
Region	Million km²	Percentage of global estimated area
Africa	1.21	9.5
Asia	2.04	16.0
Eastern Europe	2.29	17.9
Western Europe	0.29	2.3
Neotropics	4.15	32.5
North America	2.42	19.0
Oceania	0.36	2.8
Global (total)	12.76	100

52. As a visual representation, wetland groups as defined by Matthews & Fung (1987) are illustrated in Figure 1 in the appendix, which provides a broad picture of the global distribution of commonly recognised inland wetlands. This representation suffers from many of the problems outlined above. Marine and possibly many coastal wetlands are not shown. Furthermore, it has been extremely difficult to map the distribution and extent of wetlands that are only inundated intermittently or episodically. It is unlikely that a valid representation of wetland types, particularly as defined under the Ramsar Convention, is available (Finlayson et al 1999a).

53. Uncertainty over the distribution and extent of wetlands makes any impact and vulnerability assessments difficult, particularly at regional and local levels. This is further complicated by the fact that the commonly used plant-based (or morphological/structural) wetland classifications do not reflect the functioning of wetlands in terms of their hydrology and biogeochemical cycling (Sahagian and Melack 1998). A functional characterization of wetlands reflecting these functions will be needed for the importance of wetlands, particularly in global biogeochemical cycling, to be fully determined.

3.2 Summary of observed and projected global climate change

54. Changes in climate occur as a result of internal variability of the climate system and external factors (both natural factors such as solar radiation, cloud formation, and rainfall and those resulting from human activities, including increased concentrations of greenhouse gases) in the atmosphere.

55. Since the 1750s, human activities (e.g., burning fossil fuel and land use/land cover change) have increased the atmospheric greenhouse gases (e.g., water vapour, carbon dioxide, methane, nitrous oxides, and sulphur dioxide). Increase in these greenhouse gases has and will continue to increase the mean global temperature, alter the precipitation patterns, and raise sea level. This will result in an enhanced global hydrological cycle and more extreme and heavier precipitation events in many areas. Atmospheric concentrations of carbon dioxide have increased by about 30% and methane by about 150% during this period (IPCC 2001c).

56. Other greenhouse gases and the associated biogeochemical cycles have also been affected. For example, nitrogen production, due largely to chemical fertilizer production, has doubled in the 20th century (Walker et al 1999), and atmospheric concentrations of nitrous oxide have increased by about 16% (IPCC 2001c).

57. Changes in anthropogenic sulphur dioxide emissions have been large, but regionally variable, and the gas is generally short-lived. In the late 1990s, the anthropogenic sulphur dioxide emissions decreased compared to the mid-1980s, due to structural changes in the energy system as well as concerns about local and regional air pollution (Albriton & Filho et al 2001). These emissions, or aerosols, cool the atmosphere (unlike the other greenhouse gases), but are still important in explaining the changes in climate observed in the 20th century and those projected for the 21st century and beyond

Observed climate change

58. In the latest IPCC assessment, a suite of changes consistent with a warming world have been documented (Folland & Karl 2001; IPCC 2001c, see also Table 2).

59. The global surface temperature is estimated to have increased by 0.4ºC to 0.8ºC, with the rate of warming in the 20th century being greater than that in the past 1000 years, with the 1990s being the warmest decade of the millennium. Global land surface air temperatures have warmed faster than the global ocean surface temperatures. Night-time minimum temperatures have increased along with the lengthening of the freeze-free season, and thus, growing season (by about 4 to 16 days in the last four decades of the 20th century) in many middle and high latitude regions. There has been a reduction in the frequency of extreme low temperatures, without an equivalent increase in the frequency of extreme high temperatures.

60. Over the past 25 years, there has been an increase in precipitation in many parts of the northern hemisphere, with an increase in heavy and extreme precipitation events over land in the mid- and high latitudes, leading to an enhanced hydrological cycle. There has been an increase in the intensity and frequency of El Niño events that has affected drought and/or floods in many parts of the southern hemisphere. There has been a decline in the extent of Arctic sea ice, particularly in spring and summer, with about a 40% decrease in the average thickness of summer Arctic sea ice over the last three decades of the 20th century (Folland & Karl 2001; IPCC 2001c).

61. Table 2 provides further examples of observed changes in the biophysical system during the 20th century.

Table 2 Observed changes in the atmospheric greenhouse gases, climatic variables and associated changes in some biophysical systems during the 20th century (modified from IPCC 2001c).

Indicator	Observed Changes
Atmospheric concentration of CO2	From 280 ppm for 1000-1750 AD to 368 ppm in 2000 AD (31�4% increase)
Atmospheric concentration of CH4	From 700 ppb for 1000-1750 AD to 1750 ppb in 2000 AD (150�25% increase)
Atmospheric concentration of N2O	From 270 ppb for 1000-1750 AD to 316 ppb in 2000 AD(17�5% increase)
Global mean surface temperature	Increased by 0.6�0.2�C over the 20th century; land areas warmed more than the oceans
Northern Hemisphere surface temperature	Increased over the 20th century greater than during any other century in the last 1000 years; 1990s warmest decade of the millennium
Continental precipitation	Increased by 5-10% over the 20th century in the northern hemisphere; decreased in some regions, e.g., north and west Africa and parts of the Mediterranean
Heavy precipitation events	Increased at mid- and high northern latitudes
Global mean sea level	Increased at an average annual rate of 1 to 2 mm during the 20th century
Duration of ice cover of rivers and lakes	Decreased by about two weeks over the 20th century in mid- and high latitudes of the Northern Hemisphere
Arctic sea ice extent and thickness	Thinned by 40% in recent decades in late summer to early autumn and decreased in extent by 10-15% since the 1950s in spring and summer
Non-polar glaciers	Wide-spread retreat during the 20th century
Snow cover	Decreased in area by 10% since 1960s
Permafrost	Thawed, warmed and degraded in parts of the polar regions
El-Niño events	More frequent, persistent and intense during the last 20-30 years compared to the previous 100 years

Projected climate change

62. The Working Group I report of the IPCC Third Assessment (IPCC 2001a) has provided revised global, and to some extent regional, climate change projections based on a new series of emission scenarios from the IPCC Special Report of Emissions Scenarios (SRES).

63. The SRES scenarios consist of six scenario groups, based upon narrative storylines. They are all plausible and internally consistent, and no probabilities of occurrence are assigned. They encompass four combinations of demographic change, social and economic development, and broad economic developments (see Box 1). Each of these scenarios has its own greenhouse gas emission trajectories (Carter & La Rovere 2000). Parts of this report will refer to the A2 and B2 scenarios: A2 has high greenhouse gas emissions which continue to increase beyond 2100; and B2 scenarios have mid to low levels of greenhouse gas emissions with rates of increase showing signs of slowing by the end of 2100 (IPCC 2001a).

Box 1. The Emission Scenarios of the Special Report on Emission Scenarios (SRES)

A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in the mid-21st century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building, and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (A1FI), non-fossil energy sources (A1T), or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end-use technologies).

A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than in other storylines.

B1. The B1 storyline and scenario family describes a convergent world with the same global population (which peaks in mid-century and declines thereafter) as in the A1 storyline, but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.

B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, albeit at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.

64. Using the full range of SRES scenarios, the mean atmospheric carbon dioxide (CO2) concentrations are projected to increase from the 1990 level to 475 - 1100 ppm by 2100 (see Table 3). The mean global temperatures are projected to be 1.4°C to 5.8°C higher by 2100 with a great deal of variation in the regions, but generally the temperatures increasing most in the mid- to high latitudes of the northern hemisphere (see figure 2). The changes in precipitation are small (5% to 20% at regional scale) with generally an increase in year to year variation. There is generally an increase in the precipitation in the northern hemisphere and a decrease in the mid-latitudes with some increase in the tropics projected by 2100 (see Figure 3). Given the increases in temperature, the overall effect would be an increase in evapotranspiration in the tropics and a decrease in run-off affecting some wetlands. The sea level rise projections are 10-90cm by 2100 (Table 3), which could be due to thermal expansion of sea water and loss or decrease in glaciers and ice-sheets.

65. Many of the impacts on wetlands may be due not only to changes in the mean climatic variables described above but also to changes in the frequency and intensity of extreme climatic events. Examples of such projected changes include an increase in the number of hot days, fewer cold days, more heavy precipitation events, and increased frequency and intensity of floods and droughts (see Table 4).

Table 3 Climate change and greenhouse gas (GHG) concentration projections for the 21st century, if no climate policy interventions are made (modified from IPCC 2001c).

Indicators	2025	2050	2100
CO₂Concentration	415�460 ppm	460�625 ppm	475�1100 ppm
Global Mean Temperature Change from 1990	0.4�1.1�C	0.8�2.6�C	1.4�5.8�C
Global Mean Sea-Level Rise from 1990	2�15 cm	5�30 cm	10�90 cm

71. It appears that climate change will have its most pronounced effect on wetlands through alterations in hydrological regimes: specifically, the nature and variability of the hydroperiod and the number and severity of extreme events.

72. However, other variables related to climate may play important roles in determining regional and local impacts, including increased temperature and altered evapotranspiration, altered biogeochemistry, altered amounts and patterns of suspended sediment loadings, fire, oxidation of organic sediments, and the physical effects of wave energy (IPCC 1998; Burkett & Kusler 2000; USGCRP 2000).

73. Some broad projected impacts of climate change to specific types of wetlands are outlined in Table 5. It is acknowledged from the outset that the effect of climate change on all elements of biodiversity requires further analysis. A first analysis is currently being undertaken by the IPCC following a request from the Subsidiary Body for Scientific, Technical and Technological Advice (SBSTTA) of the Convention on Biological Diversity (IPCC 2002).

74. The following global summary of potential effects on wetlands addresses the various wetland types as discussed by the relevant chapters within IPCC (2001b) and other relevant reports. These include the impact of climate change on: lakes and streams, other inland wetlands, and coastal wetlands which are described separately for beaches, deltaic, mangrove and salt marsh communities, and coral reefs.

75. Given the range of information sources, and the various approaches and/or scenarios used to predict impacts, in most cases it is not possible to assign levels of confidence to the majority of the projected impacts of climate change on wetlands. Thus, the information in the following sections should be seen as a review of the range of the documented possible impacts on wetlands due to climate change (including sea level rise) that may or may not occur depending on the eventual extent of climate change, as well as the ability of wetlands to adapt to it or for humans to implement adaptation options.

Table 5 Projected impacts in some key water-based systems and water resources under temperature and precipitation changes approximating those of the SRES scenarios (modified from IPCC 2001c)

Indicators	2025	2100
Corals	Increase in frequency of coral bleaching and death of corals	More extensive coral bleaching and death Reduced species biodiversity and fish yields from reefs
Coastal Wetlands and Shorelines	Loss of some coastal wetlands to sea level rise Increased erosion of shorelines	More extensive loss of coastal wetlands Further erosion of shorelines
Ice environments	Retreat of glaciers, decreased sea ice extent, thawing of some permafrost, longer ice free seasons on rivers and lakes	Extensive Arctic sea ice reduction, benefiting shipping but harming wildlife (e.g. seals, polar bears, walrus) Ground subsidence leading to changes in some ecosystems. Substantial loss of ice volume from glaciers, particularly tropical glaciers
Water supply	Peak river flow shifts from spring toward winter in basins where snowfall is an important source of water	Water supply decreased in many water-stressed countries, increased in some other water-stressed countries
Water quality	Water quality degraded by higher temperatures Water quality changes modified by changes in water flow volume Increase in salt-water intrusion into coastal aquifers due to sea level rise.	Water quality effects amplified
Water demand	Water demand for irrigation will respond to changes in climate; higher temperatures will tend to increase demand	Water demand effects amplified.
Floods and droughts	Increased flood damage due to more intense precipitation events Increased drought frequency	Flood damage several fold higher than "no climate change scenarios" Further increase in drought events and their impacts

Lakes and streams

76. Unless otherwise acknowledged, the information presented for lakes and streams is summarised from Gitay et al (2001). Responses of lakes and streams to climate change include: warming of rivers and associated availability of thermal refuges, reductions in ice cover, reduction of dissolved oxygen in deep waters, altered mixing regimes, changes in the interaction between waters and their watersheds, alterations in flow regime, changes in biogeochemical cycling, greater frequencies of extreme events including flood and drought, changes in growth, reproduction and distribution of organisms, and poleward movement of climate zones for organisms (USGCRP 2000).

77. The only limnological properties measured or simulated at a global scale are lake and river ice phenologies. It is apparent that ice cover durations for inland waters are decreasing, and in some regions have most likely been doing so since the early 1700s. Climate change simulations (at 2× CO2 change) indicate further significant decreases in ice cover duration and ice thickness. Associated with these effects will be changes to the processes that ice cover and associated ice break-up flooding can influence. Some of these include gas exchange with the atmosphere, erosion and deposition, nutrient cycling, aquatic organism habitat availability through changes in pH and dissolved oxygen, seasonal succession, biodiversity, and primary production.

78. Changes in temperature and precipitation can impact fisheries through changes in abundance, distribution and species composition. Fisheries in small rivers and lakes are believed to be more susceptible to changes in temperature and precipitation than those in large rivers and lakes. Aquaculture activities will be affected in various ways, but will also probably adapt better than wild fisheries. Higher temperatures will probably result in higher growth rates of many species, but will also bring the threat of more disease. In addition, more food will be required to support the higher growth rates.

79. Warming will alter species abundance, distribution and composition. It is thought that the rate of migration of less mobile aquatic species, such as some fish and molluscs, will be unable to keep up with the rate of change in freshwater habitats. Distributions of fish are forecast to move poleward, with cold water fish being further restricted in their range, and cool and warm water fish expanding in range. Aquatic insects, which have an aerial life stage, will be less likely to be restricted.

80. The invasion of exotic species will become a bigger problem for lake and stream ecosystems under warmer conditions. In conjunction with current human activities (e.g., impoundment construction) the warmer, drier conditions will further threaten natural habitats and biodiversity. This could be manifested in greater temperature and dissolved oxygen stratification of inland lakes and subsequent death of some fish and macro-invertebrate species (Talling & Lamoalle 1998). At high latitudes warming is expected to increase biological productivity, whereas at low latitudes the boundaries between cold and cool-water species may change and possibly lead to extinctions (IPCC 1996).

81. Little is known about the combined effects of climate change with those human activities already influencing lakes and rivers. The influence of climate change on water quality issues such as eutrophication is unclear, particularly because many of the climate-influenced processes leading to eutrophication (e.g., precipitation, snow melt, ice cover, runoff, thermal stratification) have interacting and often opposing effects. Thus, effects of climate change on nutrient recycling will most likely be site-specific and could lead to either a greater or reduced susceptibility to eutrophication. Impacts on other water quality problems, such as acidification and chemical contamination, are also uncertain, although it is apparent that they will be influenced by climate change to some degree.

82. Finally, some of these impacts of climate change on lakes and streams will have consequences for recreational, domestic and industrial uses of lake and river water resources. They will also be intertwined with adaptation and mitigation measures: for example the building of further dams to store water for domestic and irrigation purposes could further block migration routes for many fish species and change shallow water or semi-permanent aquatic habitats into permanent deepwater habitats. This would exacerbate the negative effects of large dams, as identified in the Report of the World Commission on Dams (World Commission on Dams 2000).

Other inland wetlands

83. Unless otherwise acknowledged, the information presented for other inland wetlands is summarised from Gitay et al (2001). This section covers inland wetland habitats defined as "any area of land where the water table is at or near the surface for some defined period of time, leading to unique physio-chemical and biological processes and conditions characteristic of shallow flooded systems". However, the majority of information presented relates to peatlands. This reflects the lack of work at a global scale on other inland wetlands, which are often controlled by local hydrology. Further information on such wetlands is provided, where available, in the regional summaries of climate change impacts (section 4).

84. The potential impacts of climate change on wetlands are based on studies assessing the effects on wetland plant communities of climate variability and overuse of water resources. The effects generally involve the replacement of original wetland species with other types of wetland species (e.g., succession of swamp and fen peatland communities to bog peatland communities) or forest or heathland species, and associated effects. Related to this, climate warming could promote the invasion of alien species and the range expansion of existing alien species.

85. It is thought that the response of wetland plant communities may greatly influence the species diversity of wetland ecosystems. However, the natural temporal and spatial variability of wetland communities due to variability in water supply is a key factor, and one that makes it difficult to predict impacts of climate change.

86. Sea level rise may affect a range of freshwater wetlands in low-lying regions. For example, in tropical regions low-lying floodplains and associated swamps could be displaced by salt water habitats due to the combined actions of sea level rise, more intense monsoonal rains, and larger tidal/storm surges (Bayliss et al 1997) (see Table 5). Such changes will result in dislocation, if not displacement, of many wetland species, both plants and animals. Plant species not tolerant to increased salinity or inundation could be eliminated whilst salt-tolerant mangrove species could expand from nearby coastal habitats.

87. Migratory and resident animals such as birds and fish may lose important staging, feeding and breeding grounds. These scenarios have been outlined for the low-lying floodplains in northern Australia (Eliot et al 1999). Large scale species changes in the Volga delta (Russia) over a number of decades may provide guidance on the extent of fluctuations in both plant and animal populations in response to rising sea levels. It is apparent that the distribution of many plant species, e.g., the lotus lily Nelumbo nucifera and the reed Phragmites australis, has changed enormously, as have bird and fish populations (Finlayson et al 1993).

88. Climate change may also affect the wetland carbon sink, although the direction of the effect is uncertain due to the number of climate-related contributing factors and the range of possible responses. Any major change to the hydrology and vegetative community of a wetland will have the potential to affect the carbon sink. The impact of water level draw-down in northern latitude peatlands has been well studied and is thought to provide some insight for climate change impacts. Vegetation changes associated with the water draw-down resulted in increased primary production, biomass, and slower decomposition of litter, such that the net carbon accumulation rate remained unchanged or even increased. However, other aspects of climate change, such as longer and more frequent droughts and thawing of permafrost, will most likely have negative effects on peat carbon balance. In addition, human activities such as agriculture and forestry will also continue to transform wetlands and reduce overall wetland area, potentially resulting in losses of stored carbon.

89. The extent of biodiversity loss or dislocation from inland habitats as a consequence of climate change will be difficult to discern from other existing pressures. However, it can be assumed that large-scale change to these habitats will result in species changes. Vegetation zones, such as those in high latitudes and altitudes, and presence of species may change in response to temperature and inundation patterns. The extent of such change is unknown. White et al (1999) predict that boreal forests will extend northwards into the tundra, and also southwards in Asia. Similarly, fish migrations will be affected by both temperature and flow patterns.

90. The most apparent faunal changes may occur with migratory and nomadic bird species that use a network of wetland habitats across or within continents, respectively. The cross-continental migration of many birds is at risk of being disrupted due to changes in habitats (see references in Walther et al 2002).

91. Disruption of rainfall and flooding patterns across large areas of arid land will similarly adversely affect bird species that rely on a network of wetlands and lakes that are alternately or even episodically wet and fresh and drier and saline (Roshier et al 2001), or even a small number of wetlands such as those used by the banded stilt Cladorhynchus leucocephalus ,which breeds opportunistically in Australia's arid interior (Williams 1998).

92. Responses to these climate-induced changes may also be affected by adaptation and mitigation actions that cause further fragmentation of habitats or disruption or loss of migration corridors, or even by changes to other biota, such as increased exposure of wading birds to predators (Butler and Vennesland 2000).

Coastal wetlands

93. Unless otherwise acknowledged, the information presented for coastal wetlands is summarised from McLean & Tsyban et al (2001).

94. Potential impacts of climate change and sea level rise on coastal systems include: increased coastal erosion; more extensive coastal inundation; higher storm surge flooding; landward intrusion of seawater in estuaries and aquifers; changes in surface water and groundwater characteristics; changes in the distribution of pathogenic organisms; higher sea-surface temperatures; and reduced sea-ice cover (Table 5). These effects can also lead to associated socio-economic impacts, which, although often relevant in many ways to wetlands, are not discussed here.

95. Responses in species' distribution from such changes are not well known, although it is known that many species in coastal wetlands respond to even small changes in water levels. Warren & Niering (1993) project that rapid sea level rise will result in shifts in species' compositions, a reduction in productivity, and loss of other wetland functions. These changes will be manifest across many species and greatly influenced by interactions between the species.

96. Many coastal wetlands, for example coral reefs, beaches, salt marshes, and mangrove communities, provide significant coastal protection and thus contribute substantially to the resilience of coastal systems. However, many of these are also identified as being sensitive to accelerated sea level rise. Areas identified as sensitive to accelerated sea level rise in the Second Assessment Report of the IPCC (Bijlsma et al 1996) included low-elevation coral atolls and reef islands, as well as low-lying deltaic, coastal plain and barrier coasts, and their associated wetland habitats (i.e. beaches, estuaries, lagoons, salt marshes, mangroves). Nichols et al (1999) project that coastal wetlands in the Mediterranean, the Baltic, and to a lesser extent along the Atlantic coast of Central and North America and the smaller islands of the Caribbean will be under threat if not lost due to future sea level rises.

Beaches

97. Climate change and sea level rise are expected to change prevailing ocean wave heights and directions, as well as the magnitude of storm waves and surges, such that seawater will reach higher elevations on land than at present and will extend further inland. Thus, erosion of sandy shorelines will be more likely given expected accelerated sea level rise over the coming decades. The possible loss of nesting habitat for marine turtles that are already under human pressure worldwide is one major consequence of such erosion or, indeed, of redeposition of sediments.

Deltaic coasts

98. Deltaic regions will be particularly susceptible to accelerated inundation, shoreline recession, wetland deterioration, and interior land loss. In addition, given that the characteristic sediment deposition in deltas results in natural dewatering and compaction, such areas are already prone to subsidence. The pressures of human activity on deltaic regions are also great, further increasing their susceptibility.

99. In situations where sediment delivery is greatly reduced (usually due to upstream river regulation/diversion), marine processes will begin to dominate, and substantial coastal land loss can result from wave and surge erosion. Another potential impact of sea level rise on deltaic regions is saltwater intrusion of freshwater aquifers and even surface waters (Li et al 1999).

100. The biodiversity loss from deltaic coasts is already high in many areas, and speicies diversity could decrease further with loss of habitat for breeding birds and fish (Li et al 1999). Such change will also exacerbate recent large loss of vegetation and habitat in many deltas, such as the Mekong delta (Hollis 1998; Mitsch et al 1998), and change in habitats alongside other deltas, for example the coastal lagoons of the Volta delta (Finlayson et al 1999b). Mitsch et al (1994) provides a summary of the status and biotic importance of deltaic wetlands.

Mangrove and salt marsh communities

101. Nicholls et al (1999) predicted that by the 2080s, 22% of the world's coastal wetlands, specifically salt marshes, mangrove forests, and inter-tidal habitats, could be lost due to sea level rise alone. Combined with other human-related pressures, coastal wetland loss could be as high as 70% (Nicholls et al 1999).

102. The current exploitation and destruction of mangrove forests is reducing the resilience needed to accommodate sea level rise and storm waves and surges. Predicted responses of mangroves to sea level rise vary from little adverse impact to collapse. It is likely that responses of mangroves to sea level rise will be influenced also by other factors, such as sediment supply/flux, presence of suitable substrate, stand composition and status, and tidal range.

103. Mangrove communities may be able to migrate in response to seal level rise, but only where there exists adequate sediment supply and substrate and if sea level rise is not too rapid. In addition, the extent of coastal development will also affect the ability of coastal wetland communities to migrate in response to sea level rise (Nicholls et al 1999).

104. Responses of salt marshes to sea level rise will also be influenced by factors such as sediment supply and the nature of the backshore environment. Sufficient sediment delivery is required for vertical accretion of salt marshes to protect them from inundation by seawater. Tidal marsh (vertical) accretion is known to track sea level rise, such that the inundation of the marsh surface is not likely to be a major concern. However, in some areas, sea level rise may be too fast for accretion to keep up.

Coral reefs

105. The major aspects of climate change that could affect coral reefs are sea level rise, increased sea surface temperature, and elevated levels of CO2 in the atmosphere subsequently affecting the CO2 levels in the water.

106. Recent coral reef bleaching events around the world have re-ignited the debate about the impacts of climate change on coral reefs (Hoegh-Guldberg 1999; Wilkinson 1999). According to Wilkinson (2000), approximately 27% of the world's coral reefs have been effectively lost, with over half of that loss being due to the massive climate-related coral bleaching event of 1998.

107. Some studies suggest that maximum vertical accretion rates of healthy coral reef flats will be sufficient to accommodate the expected rate of sea level rise. However, the adaptive ability of reefs that are already degraded and under continuous stress from many human activities is less clear, and it cannot be assumed that the threat of sea level rise to coral reefs is minor. In addition, the prospect of more frequent bleaching events due to higher sea surface temperatures (see below), as well as of reduced reef calcification due to doubling of CO2 concentrations in the atmosphere, suggests that vertical accretion rates may not be able to keep pace with sea level rise.

108. Of major concern for coral reefs is rising sea surface temperatures. With sea surface temperatures expected to rise by 1-2°C by 2100 (see section 3.1), coral reefs will be under greater threat from bleaching and possibly death. However, there remains some debate concerning whether recent coral bleaching events were attributable to global warming, particularly considering the range of other pressures coral reefs are already under (e.g., pollution, increased sedimentation, over-harvesting of aquatic life including corals, predation and disease, and extreme natural events).

109. Sea surface temperatures of >1°C above seasonal averages can result in bleaching events, although the magnitude of effects (ranging from reduced growth and reproductive capacity to death) vary depending on factors such as the magnitude and duration of the temperature anomaly and, in some cases, water depth. Bleaching events have also been related to major El Niño events, during which seasonal maximum temperatures are exceeded by at least 1°C (Hoegh-Guldberg 1999). The implications of this are obvious given the projection of a more El Niño-like mean state in the tropics and increased intensity of El Niño-like events.

110. Other climate change-related factors that could affect coral reefs include altered ocean circulation patterns influencing the dispersal and transport of coral larvae, and increased frequency and/or intensity of severe weather events further damaging coral reefs and disrupting recovery (Westmacott et al 2000).

111. Corals species display differential susceptibility to increased sea surface temperature and bleaching. Consequently, extensive coral bleaching will likely lead to reduced coral diversity, habitat diversity, and overall species diversity. Such impacts could also have adverse effects on fish populations and other marine and coastal resources that are important for human livelihood (Wilkinson 1999).

4. Regional impacts of climate change on wetlands

112. The IPCC uses eight regions for its regional assessments: 1) Africa, 2) Asia, 3) Australia and New Zealand, 4) Europe, 5) Latin America, 6) North America,, 7) Polar regions, and 8) Small Island States (figure 4a). These regions are used in this section, since much of the information presented is derived from IPCC reports. The IPCC regions are broadly but not wholly similar to those used by the Ramsar Convention (see Figure 4).

113. Section 4.1 provides an overview of key projections of regional climate change, based on the latest IPCC assessment reports. Following this, for each IPCC region the wetland distribution is summarised, and the impact of climate change on wetlands is reviewed (sections 4.2 to 4.9). As with the global assessments (section 3.3), the impact of climate change is described separately for lakes and streams, other inland wetlands, and coastal wetlands.

4.1 Summary of projected regional climate change

114. The SRES scenarios have only been available for a very short time, and thus it has not been possible to include regional impact assessments based upon these scenarios. The impacts assessments in the Third Assessment Report of the IPCC, described here, use climate projections which tend to be based on equilibrium climate change scenarios (e.g., 2xCO2) or the scenarios used in the Second Assessment Report (i.e., the IS92 series), which projected global mean surface temperature of about 2 to 3 °C.

115. The two SRES scenarios are used to illustrate the projected surface temperatures and precipitation changes in different regions (see Figures 2 and 3 in the appendix).

116. Except for the Arctic, the sea surface temperatures are projected to warm less than the land and this could result in the coastal areas warming less than the interiors of the continents (see Figure 2). Projected changes in global surface temperatures include:

4.2 Africa

Wetland habitats and distribution

118. Wetland distribution and extent in Africa were reviewed by Stevenson & Frazier (1999a, see also Figure 1), who provide a figure of 121-125 million ha, about 4% of the land surface, which they considered to be an underestimate. More than 85% (~107 million ha) of this area was classed as inland wetland, with less than 10% being coastal/marine (~9-11 million ha) and 5% being artificial (~4.6 million ha). Large areas of inland wetlands are known to occur in Chad (~13 million ha), the Congo basin (~26 million ha), Nigeria (~5.5 million ha), Uganda (~4.5 million ha) and Sudan (~4.2 million ha). Nigeria also supports a large area of coastal wetlands (1.3 - 3.2 million ha).

Effects on wetlands and wetland species

119. Unless otherwise acknowledged, the information presented for the African region is summarised from chapter 2 of IPCC (1998) (Zinyowera et al 1998) and chapter 10 of IPCC (2001) (Desanker & Magadza, et al 2001).

Lakes and streams

120. Both the historical data and climate model simulations concur that water crises are imminent in large parts of Africa. The major impacts of climate change on African water systems will be through changes in the hydrological cycle, temperature, and rainfall.

121. Apart from the Zambezi/Congo Rivers, the major African rivers traverse semi-arid to arid lands before reaching the coast. Consequently, their discharge relative to catchment size is very small, with the water resource already under pressure from human activities. Elevated temperatures will enhance evaporative losses, and as precipitation is expected to decrease in the semi-arid to arid regions, runoff and discharge will most likely be further reduced. Many river systems already experience high evaporative losses, which in addition to infiltration/permeation, result in runoff to precipitation ratios of around 0.1.

122. Estimates of changes in precipitation and evaporation for 11 of Africa's major river basins indicate that eight of the systems could experience an overall decrease in runoff (Arnell 1999). These included the Volta in west Africa, the Shabeelle in northeast Africa, the Ogooue in west central Africa, the Rufiji, Ruvuma and Limpopo in east Africa, and the Zambezi and Orange in southern Africa (Arnell 1999). In the savanna regions, the frequency of seasonal flow cessation may be increasing, and periods of drought now represent critical water shortages for human use and biodiversity.

123. The impact of climate change on the Nile is highly uncertain, with predictions ranging from increased precipitation and flow to decreased precipitation and flow. Regardless of the precise impacts, the Nile is considered to be very sensitive to climate change, particularly climate warming, because of its low runoff efficiency and high dryness index. It is predicted that a reduction in flows of over 20% would exceed current transboundary management capabilities and result in major socio-economic impacts. The runoff and discharge of the River Gambia is also very sensitive to climate change variables, and discharge reductions are expected to result in increased saltwater intrusion. Sea level rise is expected to further exacerbate saline intrusion. The River Zambezi will probably experience the most extreme changes in precipitation (-10 to -20%), evaporative losses (+15 to +25%), and runoff (-26 to -40%), and combined with impoundment and land use change, impacts to this river system will probably be substantial.

124. Water storage in lakes and reservoirs is expected to be significantly affected by changes in precipitation and enhanced evaporation. Historical records indicate that many lakes and reservoirs have either ceased to have an outflow or have dried completely during drought conditions. Higher temperatures and less rainfall would further increase evaporative losses, while lake water temperatures will also increase. Even in the tropics, where temperatures are expected to rise less than in temperate regions, the changes may be sufficient to dramatically alter water levels, mixing regimes, and productivity.

125. Temperature increases may benefit lake and riverine fisheries, although the responses will vary spatially. In lakes, the responses will also be limited by carrying capacity and possibly influenced by eutrophication. However, reductions in precipitation and runoff may result in adverse effects on freshwater fisheries, as has been found during drought conditions in Lake Kariba, Zimbabwe. It should be noted that increases in fish production for fisheries do not necessarily equate to positive impacts for fish diversity, as the thermal tolerances of temperature-sensitive species are exceeded.

Other inland wetlands

126. There appears to be little information on climate change impacts to other inland wetlands in Africa. This is likely to be a reflection of the region's perspective of water availability as a resource and human health issue rather than a conservation and biodiversity issue. Nevertheless, it is recognised that a significant reduction in rainfall or increase in evapotranspiration in Angola would threaten the Okavango delta wetland in Botswana. This situation would almost certainly apply to most inland wetland habitats in semi-arid, arid, and southern Africa, and possibly also in the Sahel (northeast Africa). In addition to the Okavango delta, other major wetland systems such as the Kafue River floodplains, Lake Bangweulu, and the Caprivi Strip wetlands support a rich and diverse fauna, in particular avifauna, that may be threatened by climate change.

127. Although not specifically mentioned in relation to wetlands and their conservation, Desanker & Magadza et al (2001) identified a range of issues that are relevant to wetlands:

Coastal wetlands

128. The coastal nations of west and central Africa, from Senegal to Angola, have low-lying lagoonal coasts that are susceptible to erosion, inundation, and extreme storm events. Consequently, these regions will be threatened by sea level rise and will have difficulties adapting due to rapid urban expansion along the coast. For example, in Senegal, a 1-m rise in sea level could inundate and erode more than 6,000 km2 of land, much of which is wetlands.

129. In addition, a number of African coastal areas that are threatened by sea level rise offer unique habitat for migratory bird species. It is anticipated that the Arctic breeding grounds for these species will be adversely affected by climate change (e.g., Lindstrom and Agrell 1999), but there is far less information available on the effect on waterbird populations using the wintering grounds across Africa. The absence of good quality monitoring data for many African wetland birds will constrain any further assessment.

130. Sea level rise may also lessen the protective function of reefs along the east coast of Africa, increasing the potential for coastal erosion. To the northeast, the coastal areas of Egypt, including around Cairo and the Nile, are also threatened by sea level rise, and substantial parts of the Nile delta could be lost as a result of increased inundation and erosion.

131. The anchovy fishery in the southwest of Africa may be impacted by climate change. Essentially, recruitment in the species is influenced by water temperature and upwelling of nutrient-rich waters, both of which are linked to global climatic conditions. Thus, changes to both factors would most likely have severe impacts on the fishery. In addition to being an important fishery species, the anchovy is also recognised as a key element in the food chain for many other fish species, aquatic mammals, and birds.

4.3 Asia

Wetland habitats and distribution

132. Wetland distribution and extent in Asia is not accurately known (Watkins & Parish 1999). There are an estimated 204 million hectares, excluding Russia but including some 7.4 million ha in the Middle East (Frazier & Stevenson 1999, see also Figure 1), but the reliability of these figures is unknown. Mangroves cover an estimated 7 5 million ha, with much of this occurring in Indonesia (~4.3 million ha). Peat swamps are also common, but as with much of the inventory available for Asia, differences in definition and delineation undermine the value of these estimates, which include 17-27 million ha in Indonesia, ~2.5 million ha in Malaysia and 1-3 million ha in China. Coral reefs cover around 2.7 million ha in the Philippines, and rice fields across all of Asia cover an estimated 133.6 million ha.

Impacts of climate change on wetlands and wetland species

133. Unless otherwise acknowledged, the information presented for the Asian region is summarised from chapters 7, 10 and 11 of IPCC (1998) (Gitay & Noble et al 1998; McLean et al 1998; Yoshino & Jilan et al 1998) and chapter 11 of IPCC (2001) (Lal et al 2001).

Lakes and streams

134. There is concern that climate change may accelerate the damage to lakes and rivers (and other wetlands) already caused by environmental pollutants, exploitation of natural resources, transformation of lands, and recreational activities. It is likely that changes to runoff and river discharge as a result of climate change will place further pressure on water resources that are already under increasing demand due to population growth, urbanisation, industrialisation, and, in particular, agriculture (McLean et al 1998).

135. Predicted changes in runoff modelled according to changes in precipitation and evapotranspiration by 2050 vary (Arnell 1999). Nevertheless, results suggest increased runoff in northern boreal Asia, temperate Asia and central tropical Asia, and decreased runoff in southern boreal Asia, arid and semi-arid Asia, western tropical Asia (i.e., India; high variability between model estimates), and southeastern tropical Asia (Arnell 1999). By 2050, increased runoff in Siberian river systems is expected to cause difficulties with seasonal inundation and flooding and associated management of these problems. Runoff in temperate Asia will vary spatially, with south China possibly experiencing reduced runoff.

136. A large number of perennial rivers in semi-arid Asia are fed by snow and glacial-melt from almost 1500 glaciers in the Himalayas. The past few decades have seen the retreat of almost two thirds of these glaciers due to a range of climate and non-climate related factors. Future global warming is expected to increase the rate of glacial melting, which will likely lead to higher summer flows in some rivers for a number of decades, beyond which flow will decrease as the glaciers disappear. For countries with very large glaciers, increased runoff may persist for a century or more, substantially increasing regional water resources.

137. The snow melting season coincides with the summer monsoon season, so any intensification of the monsoon could increase the likelihood and magnitude of floods. Such impacts are expected to be greater in the western Himalayas than the eastern Himalayas, due to the greater contribution of snow melt to runoff. An increase in surface runoff during autumn and a decrease during spring are forecast for the highland regions of South Asia (i.e., from Pakistan to Bangladesh), while rising temperatures will result in greater snow melt and a raising of the snow line. This situation will further increase the risk of flooding for countries in this region. On the east coast of Malaysia, and in the coastal areas of Sarawak and Sabah, flooding usually occurs on an annual basis during the rainy northeast monsoon season; increases in the intensity and frequency of heavy rainfall during this period are expected to increase the intensity and frequency of flooding in the region.

138. With predicted temperature increases, and associated reductions in snowfalls, some lakes, including Lake Biwa and Lake Kasumigaura in Japan, are expected to be more susceptible to eutrophication and other water quality problems (Kobori 2000). Related to this, the invasion of alien species and range expansion of existing alien species (e.g., water hyacinth, Eichhornia crassipes; banana plant, Nymphoides aquatica; and Salvinia molesta) may have major implications for native aquatic plant biodiversity (Kadono 2000).

139. Lakes in northern latitudes may change from a vertically homogeneous state to being stratified, while the opposite

Projected Changes during the 21st Century in Extreme Climate Phenomena		Examples of Projected Impacts
Higher maximum temperatures, more hot days and heat waves over nearly all land areas		Increased heat stress in wildlife
Higher minimum temperatures, fewer cold days, frost days and cold waves over nearly all land areas		Extended range and activity of some pest and disease vectors
More intense precipitation events over many areas		Increased flood, landslide, avalanche, and mudslide damage Increased soil erosion Increased flood runoff could increase recharge of some floodplain aquifers
Increased summer drying over most mid-latitude continental interiors and associated risk of drought, Intensified droughts and floods associated with El Niño events in many different regions		Decreased water resource quantity and quality Increased risk of fires
Increase in tropical cyclone peak wind intensities, mean and peak precipitation intensities (over some areas)		Increased coastal erosion and damage to coastal buildings and infrastructure Increased damage to coastal ecosystems such as coral reefs and mangroves