Study On Variation Characteristics Of Different Types Of Surface Water In China From 1980s To 2019

Surface water provides abundant water for human life and production.It is an indispensable part of water cycle,regional climate regulation and ecosystem maintenance.Due to the obvious spatial differences in China’s climate,topography and economic development level,the spatial distribution of different types of surface water bodies is uneven.In the past decades,significant climate change and rapid economic and population growth have exacerbated the temporal and spatial changes of surface water in China,and triggered a series of environmental problems such as floods and droughts.Climate change and human activities are the main reasons for the change of surface water area,and have different temporal and spatial change characteristics and impact mechanisms in different regions and different types of water bodies.Therefore,understanding the temporal and spatial variation law of different types of surface water and exploring the variation reasons of different types of surface water are of great significance for the sustainable development of ecological environment and the security of water resources in China.Firstly,this paper based on the Joint Research Centre Global Surface Water(JRC GSW)distinguishes the newly added and disappeared surface water in China from1980 s to 2019 into different water types,and analyzes the spatial distribution characteristics of newly added and disappeared surface water in China.In order to understand the reasons for the increase and disappearance of surface water of various water types,typical areas were selected,and the reasons for the temporal and spatial changes of surface water of various water types were analyzed in combination with historical images,important events and existing research.Finally,in order to deeply analyze the annual change of surface water area and accurately quantify the change characteristics of inland surface water in,the concept of equivalent water area is introduced.Taking Northeast China as an example,the Northeast surface water in 2020 is classified to obtain the spatial distribution characteristics of various types of water bodies.The time series of surface water equivalent water area of different types of water bodies for 22 consecutive years from 1999 to 2020 are extracted,the temporal and spatial variation characteristics of surface water in Northeast China are analyzed,and the interannual variation laws and causes of permanent water bodies and seasonal water bodies are discussed in combination with precipitation and other climate data.The main research work and results are as follows:(1)Firstly,uses JRC GSW water body data set to obtain the newly added or disappeared surface water with a national area of more than 0.1 km~2 from 1980 s to2019.Combined with multi-source remote sensing data and historical images,this chapter uses semi-automatic method to classify the newly added or disappeared surface water bodies according to water body types,and statistics the spatial distribution characteristics of surface water with different water body types in provincial administrative units.The results show that the newly increased surface water area in China from 1980 s to 2019 is about four times that of the disappeared water area.On the whole,the surface water area in China shows an upward trend,with a net growth area of35071.71 km~2.The newly added water bodies are mainly distributed in the East and west of China,while the disappeared water bodies are mainly distributed in the east of China.Among all surface waters,lake type surface water has the largest increase area,accounting for about 2 / 5 of the new water body area in China.The disappearing area of coastal surface water is the largest,accounting for about 3 / 10 of the disappearing water area in China,and the coastal is the only water type with negative net growth area among all water types.Combined with historical images,historical data and existing literature,this paper analyzes the reasons for the change of surface water area in typical areas with large area of newly added and disappeared surface water.The results show that:(1)In terms of lake surface water,there are 1035 lakes greater than 1 km~2 in Tibet Autonomous Region,of which about 788 lakes have increased in area.The main reason for the increase is the rapid expansion of Lake area affected by rainfall after 2000.Due to shallow water and wide lakes,Baiyangdian has a large amount of evaporation and infiltration into the river.The government has restored the water storage of Baiyangdian by taking reservoir water supply and South-to-North Water Transfer.In the middle and lower reaches of the Yangtze River,due to the conversion of farmland to lakes and the transformation of agricultural or construction land into aquaculture areas,the area of natural and artificial lakes has been restored.(2)In terms of reservoir type surface water,there are 941 reservoirs greater than 0.1 km~2 in Heilongjiang Province from 2019,of which about 374 reservoirs have increased in area,with a total increase area of 803.48 km~2.The successful construction of reservoirs and the start of water storage are the main reasons for the increase of reservoir area.(3)In terms of coastal surface water,the disappearance area of Hangzhou Bay in Zhejiang Province is relatively large.The reason is that the land in Hangzhou Bay has gradually become an impermeable layer in order to supplement land resources and reclaim land from the sea.The seashore of Shandong Province disappeared 352.43 km~2,increased by 380.97 km~2,with a net increase of 28.54km~2.Seawater erosion and sediment deposition carried by the Yellow River are the main reasons for the addition and disappearance of seashore respectively.(4)For Heilongjiang,where the river surface water changes significantly,the area of newly added river water bodies is distributed in the middle and upper reaches of the Songhua River.The reason for the increase is that the local government has built river channels to prevent water and soil loss,and the rivers have formed more concentrated and stable water areas.While the disappeared river water bodies are mainly distributed in the lower reaches of the Nenjiang River and the lower reaches of the Songhua River.On the one hand,the disappearance is due to the water storage in the upper reaches,the reduction of water volume in the lower reaches,and the local reclamation of the original river channels into cultivated land,Surface water disappeared.(3)In order to better understand the continuous change characteristics of different types of water area,this chapter selects the northeast region with rich surface water types,distinguishes different water types with reference to its surface water distribution in 2020,calculates the equivalent water area of surface water of different water types from 1999 to 2020 to accurately quantify the annual inland surface water area,and analyzes the temporal and spatial change characteristics of various types of surface water.The results show that in 2020,the equivalent water area of surface water in Northeast China is about 33009 km~2,mainly distributed in the middle and East,and the area of seasonal water body is slightly larger than that of permanent water body.The surface water in Northeast China is divided into six types: lake type,reservoir type,river type,coastal aquaculture area type,swamp type and other unconventional water bodies.Among the six water types,unconventional water bodies have the largest area,accounting for about 2 / 5 of the total surface water area in Northeast China,which are concentrated in the central and southeast regions.The water bodies in coastal aquaculture areas are mainly distributed in the rivers along the Yellow Sea and Bohai Sea.The higher the latitude,the less the proportion of reservoir water bodies,and the lower the latitude,the less the proportion of lake water bodies.Comparing the equivalent flooded area in the two 11 year periods of 1999-2009 and 2010-2020,it is found that among the six water types,only the area of lake type and coastal type water body decreases,while the area of other types of water body increases.The surface water area in the middle,East and North shows an upward trend,while the surface water area in the West and South shows a downward trend.The farther away from the central region,the more obvious the upward and downward trend of surface water area.The study also found that lake type,reservoir type,river type and coastal aquaculture area type water bodies are mainly permanent water bodies,while swamp type and unconventional water bodies are mainly seasonal water bodies.Compared with the precipitation data,it is found that the surface water area increases with the increase of precipitation in the past 22 years,especially the seasonal water area is almost consistent with the fluctuation of precipitation,while the growth of permanent water body is relatively flat.