Response Of Evapotranspiration In Balkhash Lake Basin To Changes In Ecological Environment

The Balkhash Lake basin spans China's Xinjiang(inside)and Kazakhstan(outside),and is one of the important inland lake basins in the arid zone of Central Asia.Due to the characteristics of the geographical environment,precipitation in the basin is scarce and evaporation is intense.Evapotranspiration,as an important part of the surface energy and water cycle,is of great significance to the management and protection of water resources in the basin.Since the completion of the Kapuchagai Reservoir,the largest water conservancy project in the basin in 1972,and the collapse of the Soviet Union before 1991,the ecological environment spatial pattern based on land use and land cover(LULC)in the Bahu basin has been significant Changes and further changed the evapotranspiration and its spatial distribution characteristics in the basin.In the case of changes in the ecological environment of the Bahu Lake Basin,studying the response of evapotranspiration to changes in the ecological environment can provide a scientific basis for relevant departments in water resources management and the formulation of ecological environmental protection measures.This paper takes the Bahu Basin as an example to study the response of evapotranspiration to changes in the ecological environment.First,the ecological environment data characterized by the 3 LULC data in the 1970 s,2005 and 2015 were used to quantitatively study the ecological environment changes in the basin over the past 45 years.Secondly,based on the SEBAL model,the actual evapotranspiration in the basin is simulated,and the temporal and spatial distribution characteristics of LULC evapotranspiration in different periods are summarized.Finally,combining LULC changes and evapotranspiration simulation results,the response of evapotranspiration in the river basin to changes in the ecological environment is analyzed,and suggestions and countermeasures are made for future water resources management and ecological environment protection in the river basin.The main conclusions are as follows:(1)In the past 45 years,grassland and unused land have always been the two most LULC types in the basin,accounting for more than 85% of the total.Waters are mainly distributed abroad,forest land is mainly in China,and the proportion of domestic cultivated land is higher than overseas.The domestic distribution is more even than the overseas type,but the overseas area is larger,and the distribution of LULC types in the whole river basin is consistent with that of overseas.(2)The development stages and LULC changes experienced under different socio-economic systems are different.The cultivated land and forest land in the watershed experienced a change process of first decreasing and then increasing,showing an overall increasing trend;the area of grassland and urban and rural construction land continued to increase from 60.03% and 0.35% to 63.04% and 0.57%,respectively;the change process of waters and unused land was consistent with that.Cultivated land and woodland are completely opposite.The change of cultivated land outside the country from 1970 s to 2015 is different from that of the whole watershed,and only the forest land and urban and rural construction land within the country have the same changes as the whole watershed.The change process of overseas LULC dominates the change of LULC in the whole basin.(3)The change of LULC in the watershed is dominated by two-way conversion.The change of LULC in the later period has a greater impact on the change of LULC during the whole study period,and the conversion of LULC in space has a certain time cumulative effect.Both the single type and regional LULC change trend and state index indicate that the domestic change process is more stable than that of overseas,and the whole river basin is always in a balanced state during the study period.(4)The order of evapotranspiration of different types of LULC in the basin is as follows: water area/forest land>cultivated land/urban and rural construction land>grassland>unused land.Water area and forest land are the two ecological types with the largest evapotranspiration in the basin,and the unused land has the smallest evapotranspiration.The evapotranspiration of LLC types at home and abroad is different in the order of size.The maximum evapotranspiration in China is forest land and the water area outside,and the evapotranspiration of domestic cultivated land is less than that of overseas,while the evapotranspiration of grassland is greater than that of overseas.(5)Basin evapotranspiration in the daily and monthly change of Evapotranspiration closely related to temperature.Daily evapotranspiration render similar to the temperature variation of single peak,peak came in july;great value for the month of evapotranspiration in july,consistent with temperature changes,but due to irrigation due to snow melting and there is a summit in april;evapotranspiration of daily evapotranspiration and months minimum value is january,which is the month with the lowest temperatures of the year.In addition,the Model Evapotranspiration simulation result showed a clear seasonal pattern : Summer > spring > autumn > winter.(6)physical factors such as temperature change on annual evapotranspiration had little impact,changes in different types of lulc 35 mm,the annual variation of total evapotranspiration were mainly of lulc change caused by human activities.Total evapotranspiration in the watershed year of 2005-2015 changes of farmland,woodland,grassland and increase in the urban and rural construction land,waters and does not use the reduce,and in 2005-2015 to land use / land cover(lulc)changes of ecological environment change of trend with good consistency.