*Article* **Ecological Water Demand Estimations for Desert Terminal Lake Survival under Inland River Water Diversion Regulation**

**Jinqiang Lu 1,2,3, Lingqi Li 1,2,\*, Enhui Jiang 1,2, Rong Gan <sup>3</sup> , Chang Liu 1,2 and Ya Deng <sup>4</sup>**


**Abstract:** 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 <sup>×</sup> <sup>10</sup><sup>6</sup> <sup>m</sup>3/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.

**Keywords:** lake area; water diversion; ecological water demand (EWD); minimum water level; inland river
