Service Description: Due to the withdrawal of water upstream by the Three Gorges Dam, drought and other meteorological trends, China's largest source of freshwater Lake Poyang has been shrinking since 1984. The diminish of the lake affects local land cover, economic conditions, and the livelihoods of dependent communities, devastating ecological and economic ramifications. It’s crucial to study the reduction and exploring countermeasures.
The steps and methods used in this analysis are: 1. Extracting and downloading land cover images taken by Landsat satellites between 1984 and 2014 from USGS Earth Explore; 2. classifying each image using Iso Cluster Unsupervised Classification to identify the pixels with water values; 3. Filtering the result using Majority Filter tool to remove small errors; 4. Applying Boundary Clean tool to filtering the pixelated, granular edges around the boundaries; 5. Calculating the hectares of the lake in each image to get the reduction rate over years.
It is found that the lake lost 21616 hectares from year 1984 to 2001. The shrank rate was 1271 hectare/year. From 2001 to 2014, the diminish rate was 3517 hectare/year, almost tripled compared the previous 13 years. Considering the upstream water was pulled from Yangtze River, the construction of was partially responsible for the increased diminish speed of Lake Poyang between 2001 and 2014.
To mitigate the diminished Lake Poyang situation, regulating upstream water usage and restoring and conserving the ecosystem around the Lake Poyang are recommended. On the one hand, modulating the Three Gorges Dam’s water release schedules to maintain ecological flows so that it supports Lake Poyang’s water level; on the other hand, restoring wetlands and other natural habitats around Lake Poyang so that it enhances its water retention capacity and support biodiversity.
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