Changes and driving factors of water surface area for inner lakes in Lake Dongting district in the past 40 years

Abstract

In Lake Dongting district, there are some inner lakes located at low-lying fields surrounded by protective embankments. As a result of the dual effects of climate change and human activities, the area of inner lakes had changed apparently over the past decades. In this study, changes of water surface area for inner lakes in Lake Dongting district had been surveyed, using multi-time remote sensing images from 1979 to 2016. The total area was relatively stable, while a rising trend in wet season and decreased in a fluctuation way during dry season. With the increase of lake area, the proportion and extent of area change decreased. Inner lakes larger than 5 km2 were relatively stable, while for lakes less than 5 km2, area change was particularly intense. Water surface area change of inner lakes was mainly influenced by climatic factors, such as rainfall and evaporation, and human activities of water intaking, flood control, drainage and Returning Farmland to Lake. Between 1980-2000 and 2001-2015, the average annual rainfall in both dry season and rainy season showed a decreasing trend in varying degrees in Lake Dongting district, while the average annual evaporation increased significantly, resulting in the utilizable precipitation reducing significantly. After the operation of the Three Gorges project, the diversion flow of 3 diversion outlets of Jingjiang River and the utilizable precipitation both had declined significantly, while the demand for water resources has been increasing, which resulting in reduced water surface area during dry season. In addition, severe water shortages in Lake Dongting area makes it necessary to storing stormwater as water resources, which combined with implementing Returning Farmland to Lake to increase the surface area of lakes during the wet season. For enough water supply, it is necessary to reinforce studies and conservation about inner lakes, make further efforts to return farmland to lake, and optimize the structure of rivers and the river-lake connectivity.