Desert terminal lakes are important signals to discern ecological degradation crises, particularly in arid areas where an artificial project of ecological water diversion has designated a quota of river water to prevent lake body shrinkage and protect the ecosystem. Knowledge of the minimum ecological water demand (EWD) is thus necessary to ensure the basic health of lake ecosystems. This study analyzed the spatiotemporal evolution of water boundaries using Landsat satellites data via remote sensing technology from 2002 to 2017 in East Juyan Lake, an inland desert terminal lake of the Heihe River in northwest China. The minimum lake water demand was determined using two estimation methods: the lake-evaporation-oriented EWD method and the minimum water level method. In the latter method, both lake topography (using water-level area curves) and biological survival demands (using bighead carps as indicators) were considered to derive the minimum lake EWD. Water diversion to the lake over the past 15 years has increased the lake’s area, but there are still marked intra-annual seasonal variations. The annual minimum lake water demand was suggested to be 54 × 106 m3/year by comparing the different methods; however, it was not satisfied, and the lake survival was endangered when the occurrence frequency of the annual runoff in the Zhengyixia hydrological station exceeded 65%. This study offered promising directions for inland lake water resource management.

Lakes in arid inland areas are important indicators for reflecting the regional ecosystem security under climate change and human-related impacts. Understanding the evolution characteristics of lakes is helpful for eco-environment protection and management. This study applied the Landsat remote sensing data from 2002 to 2017 to analyze the water surface area changes of East Juyan Lake, a closed lake in northwest China. The results showed that the upward trends existed from 2002 to 2006 and were more significant from 2014 to 2017. The upward trends became gentle from 2007 to 2013. Regarding the seasonal characteristics, the water surface area in winter was almost the largest in the whole year, with an annual average of 51km2, followed by that in autumn (50.45km2). The annual average value in spring (48.16km2) was larger than that in summer (41km2). For the spatial changes, the lake boundary generally expanded from 2002 to 2009, and its eastern and western boundaries changed obviously after 2006. After 2010, the changes in lake boundaries tended to be gentle.