Abstract: Drought is one of the most frequent meteorological hazards in the mid-mountain of the Koshi Basin and affects seriously the agricultural production.In this study,the meteorological and agricultural data were used to analyze the drought change and its impact on crop yield in the study area from 1998 to 2015 using the linear trend and regression analysis.The results are as follows:① The crop water stress index (CWSI) was increased at first and then decreased.In terms of CWSI,the drought disaster in the southern area was the most serious,then in the central area,and it was the lightest in the north;② The impacts of drought on different crops were significantly different.When 0.60≤CWSI<0.63,drought affected the growth rate of wheat yield per unit area.When 0.63≤CWSI<0.64,the yields of potato and wheat were affected by drought.When 0.64≤CWSI<0.65,the yields of barley,potato and wheat were affected by drought.When 0.65≤CWSI<0.66,the yields of corn,barley,potato and wheat were affected by drought.When CWSI≥0.66,the yields of corn,barley,potato,wheat and rice were affected by drought;③ There was a significant spatial difference in the impact of drought on crop yield.The critical values and impact extents caused by drought were different from different regions.

Key words: drought, crop yield, crop water stress index, spatial difference, the mid-mountain of the Koshi Basin