Change Of Water Area And Lake Evaporation Estimation Of East Juyan Lake

Arid area occupied 33% of the total world area.As a significant stress factor,water shortage leads to the intense competition between ecological environment and social economic development,which is shown markedly on the surrounding changes of terminal lake in the lower reaches of watershed basin.Located in the central Hexi Corridor,Heihe River basin is the second largest inland river basin in Northwestern China.Ejina oasis is the unique ecological barrier in Alashan League of Inner Mongolia and the important ecological defense in Northwestern China.The terminal lake,East Juyan Lake plays an important role of stopping the enlargement of land desertification.However,due to unreasonable allocation of water resources in the middle stream,East Juyan Lake began to shrink from 1940 s and went completely dry in 1995.Also Ejina oasis had deteriorated massively.Since 2000,the Ministry of Water Resources decided to implement the management project and the main stream water regulation management of Heihe River basin.Released water from every hydrologic section was controlled strictly so that it from Langxinshan Gorge is 8.881 billion cubic meters in all and the flow into lake adds up to 0.819 billion cubic meters,which has a significant effect on the ecological environment restoration,such as water area of East Juyan Lake and vegetation growth of Ejina oasis.Remote sensing technology has the characteristics of wide sensing range,abundant information and fast update time.With remote sensing as the research means,this paper selected Landsat series satellite data and develops inversion and calculation of water area and evaporation in main places of downstream during the period2002-2015 by using Surface Energy Balance System model and Modified Normalized Difference Water Index.Ecological environment changes and recovery after water regulation management are also analyzed combined with released water,climatic and social economic factors.The study finds that with the released water and flow into lake increasing,water area and evaporation shows an upward trend and stabilizes at around 40km2 and 0.09 billion m3 respectively.NDVI value of Ejina oasis also increases.Besides,ecologicalwater demand of East Juyan Lake is also obtained according to the relationship between its water storage,evaporation and area.There is time lag effect between water area and hydrological factors to some extent and water evaporation is higher than the flow into lake since 2005.The correlation between mean relative humidity(meteorological factor),economic component(social economic factor)and ecological indicators is higher.As a relatively successful case,improvement of ecologic environment in the downstream of Heihe River since management is presented in this paper,which can provide some guiding significances to ecological environment management and recovery of terminal lake and its surroundings in arid regions.