Temporal-spatial variations of NPP and its climatic driving mechanism in the Three Gorges Reservoir Area based on modified CASA model

Net primary production（NPP） in the Three Gorges Reservoir Area（TGRA） during 2001-2015 was estimated using a modified parameter CASA model. The spatial and temporal variation and distribution characteristics of the NPP were analyzed on annual and inter-annual scale based on Sen′s slope. According to the correlation analysis method, the driving mechanism of climate factors to NPP was discussed. Then, the NPP in the future was predicted with climate model simulation results as input. The results showed that:（1） from 2001 to 2015, the monthly value of NPP in the TRGA presented a single-peak seasonal variation trend, reached its maximum value of 160 gC m-2 month-1 in July. The annual variability of NPP showed a rising trend of fluctuation with a small range, and the multiyear average value of NPP was 727 gC m-2 a-1. In terms of the spatial distribution, the main features are higher in head and tail of the reservoir, lower belly of the reservoir and higher north of the Yangtze River than south.（2） The NPP was significantly positively correlated with precipitation, temperature and solar radiation, with the strongest correlation with temperature and the weakest correlation with precipitation, indicating that the vegetation productivity was more sensitive to the change of temperature.（3） In the next 15 years, the multiyear average value of NPP was 859 gC m-2 a-1, showed a slight decrease trend, with a range of 4.14 gC m-2 10 a-1. Compared with the current situation, the NPP showed a certain increase in the future. Generally speaking, the vegetation in the TGRA was growing well and developing in a benign and stable way.