Variation of drought over northern China during 1950-2000

Based on China's monthly precipitation data of 629 stations during 1950-2000, we calculated Z indices and separated them into seven Dryness and Wetness grades. Further, a drought area index was proposed to study changes in drought severity in northern China. The results revealed that the different severity of droughts all showed expanding trends in northern China's main agricultural area. Moreover, the area coverage of droughts in different seasons and different regions displayed different trends.