Abstract:Based on the agricultural flood drought data from 1950-2017 and the runoff data from 1956-2017 in Dongting Lake area, the degree and risk of agricultural flood and drought disasters and their trends in Dongting Lake area after impoundment of the Three Gorges Reservoir were analyzed by using the methods of flood and drought disaster acceptance rate, theory model of entropy information diffusion, standardized runoff index (SRI), and re-standard polar difference analysis (R/S). The results showed that:(1) After impoundment of the Three Gorges Reservoir, the rate of flood stricken decreased from 6.65% to 1.21%, the rate of flood disaster decreased from 2.97% to 0.71%, the rate of drought stricken decreased from 5.97% to 2.48%, and the rate of drought disaster decreased from 2.98% to 0.99%. (2) When the disaster rate of agricultural flood and drought disaster was more than 5%, 10%, 15%, and 20%, the probability of flood risk was 0.415, 0.192, 0.057 and 0.025, and the probability of drought risk was 0.518, 0.359, 0.037 and 0.001, respectively. The flood risk level was medium to low risk (disaster rate was more than 5%, 10%) and low risk (disaster rate was more than 15% and 20%). Drought risk level was medium risk (disaster rate was more than 5%), medium to high risk (disaster rate was more than 10%), and low risk (disaster rate was more than 15%, 20%). (3) The trend of flood and drought disasters will be a reducing trend for floods and an increasing trend for drought in studied areas.