Multiple spatio-temporal patterns of vegetation coverage and its relationship with climatic factors in a large dam-reservoir-river system

Abstract

Along with the development of large-scale hydropower projects, many changes are arising both on the river channel and the ecosystems, which leads to the formation of a dam-reservoir-river system. The system is of significance to China due to the large-scale utilization of hydropower. However, such projects may cause significant impacts on local vegetation dynamics, which is of importance to local decision makers and water resources managers. In this research, the spatio-temporal variations of normalized difference vegetation index (NDVI) and climatic factors (CFs) under multiple time scales (i.e., annual, seasonal, and wet/dry periods) and the spatio-temporal pattern of the correlation of NDVI-CFs under the scales of annual and wet season were analyzed in the system by using the statistical methods. The response of NDVI to CFs in the basin was explored at the monthly scale. The main results indicated that from 1999 to 2013, the annual average NDVI had a significant overall upward trend. The distributions of the NDVI and its trend had the spatial and seasonal differences, with majority areas showing medium-high and high vegetation cover and a slight improvement in the grade of vegetation cover change of more than 40% of the total area. In the basin, temperature (T) and evapotranspiration (ET0) showed an upward trend, and precipitation (P) and the humidity index (HI) were the opposite. The corrections of NDVI-T and NDVI-ET0 were positive, and that of NDVI-P and NDVI-HI were negative. Also, the vegetation growth was mainly affected by the amount of P, and its time-lag period to the P was two months. In the scale of the eight cascade hydropower stations, the vegetation coverage and the correlation of NDVI-CFs around the Jinanqiao and Longkaikou hydropower stations were the best, and those near the Ludila and Guanyinyan were the worst, indicating that the vegetation coverage was affected by the cascade hydropower stations development. Therefore, the results may be beneficial for sustainable watershed ecosystem management in the system, as well as ecological development planning around the cascade hydropower stations.