Abstract:

Based on Z index and entropy weight theory,the seasonal drought composite index was constructed to evaluate the drought intensity.Taken the Qilian Mountain area as an example,the characteristics and spatial distribution of seasonal drought were evaluated.The results show that drought intensity becomes weak from 1961 to 2016.The intensity of drought in spring and autumn is significantly weakened.The intensity of drought in summer is also weakened though it does not pass the significant test.In general,seasonal droughts are frequent and severe in the 1960s,1970s,and 1990s.However,the summer drought and winter drought become frequently since 2000,which should require to pay more attention.The drought intensity of four seasons sorted from severe to mild is winter,summer,spring,and autumn.In terms of drought variability,autumn is the strongest,followed by winter.Spring is the weakest.The south of the Qilian Mountains area is drier than the north in spring,summer and autumn,and vice versa in winter.Drought in winter is widespread,especially severe in the north of the Qilian Mountain area where Jiuquan is the center of this region.During the study period,the drought intensity becomes weak gradually in both north and south of the Qilian Mountain area.The drought intensity in the south becomes milder than that in the north.Drought intensity during the period of no-grass decreased significantly.This study provides a reference for the evaluation of drought in the Qilian Mountain area.

Key words: Z index, Entropy weight assignment, Drought composite index, Seasonal drought