Study On Global Wetland Simulation And Wetland Loss

Wetlands as the most productive and valuable ecosystems on the earth,are one of the most indispensable resources for human beings.However,due to the increasing human interference,wetland disappearance and degradation have occurred worldwide.Preventing the further loss of global wetlands,conservation and wise-utilization of the global wetlands calls for precise wetland datasets.Global wetland information widely disperses in various global datasets.The extensive disagreement on wetland categories existing in these different datasets leads to uncertainties in our understanding of the distribution of global wetlands.Because of the dynamic and transitional characteristics of wetlands,it is difficult to extract wetland information with one single technical means.Simulating potential distribution of wetlands can provide maximum extent of global wetlands and can be used to improve the accuracy of wetland mapping.In this paper,by combining the distributed hydrological model and remote sensing technology,I simulated the potential distribution of global wetlands.Based on the simulation result,the status of global wetland loss was estimated.The major conclusions of this paper are as following:1.The distribution of global wetlands.At present,in terms of quantity it seems that datasets related to global wetlands are adequate;however,in terms of quality,accurate datasets specifically for wetlands are scare.And these currently available datasets are widely dispersed among land cover products,water products which are either static in time or coarse in spatial resolution and have extensive disagreement of wetlands among them.Wetland area in different datasets ranges from 2.12 million km2 to 17.30 million km2.The consistency of wetland spatial distribution among them could be less than 1%.The different definitions of ?wetland‘,the intrinsic features of wetlands,and the limitations of the existing technical means contribute to these extensive inconsistencies.2.Simulation of the potential distribution of global wetlands.A new index,Precipitation Topographic Wetness index(PTWI),was proposed by revising the Climate Topographic Index(CLTI).Based on the capability to predict the spatial distribution of wetlands,the performance of PTWI was evaluated.The result indicates that the simulation result of PTWI is in better agreement with the observed wetland distribution and PTWI is better able to predict the general pattern and areal extent of wetlands at global scale.In order to avoid the complicated processes of distributed hydrological models‘ parameters acquisition and equations solution,based on the geographic characteristics of wetland distribution,I simulated the potential distribution of global wetlands by combining PTWI with the verification approach of remote sensing classification.The simulation result shows that approximately a total area of 29.83 million km2 of wetlands exist worldwide,including 11.41 million km2 of open water and 18.42 million km2 of wetland with no open water.These wetlands are mainly distributed in Asia,North America,and South America.The accuracy validation was performed in China,the conterminous United States and Europe which have high quality wetland datasets.The overall accuracy of the simulation result is nearly 69%.3.Estimation of global wetland loss.Agriculture and urbanization are two kinds of human activities which cause wetland disappearance directly.By using the global land cover product,GlobCover2009,the spatial boundaries of agriculture and urbanization were extracted and used together with the potential distribution of global wetlands to estimate the global wetland loss.The estimation result demonstrates that as of 2009,the world has lost at least 33% of its wetlands in area,including 2.64 million km2 of water and 4.58 none water wetlands.The largest wetland loss has occurred in Asia with about 2.65 million km2.And the most serious situation of wetland loss comes from Europe,which has lost 45% of its wetlands.Although the least wetland loss happens in Oceania with about 0.18 million km2,its wetland loss rate reminds us not to ignore the wetland demise in this region.In contrast,the situation of wetlands in North America is relatively optimistic,only 8% of wetlands have been disappeared in this continent.