Spatial And Temporal Variation Of Drought And Its Impact On Vegetation In China During 1960-2014

Drought,which has the characteristics of high frequency,long duration and wide impact,is one of the most affected natural disasters in the world and is threatened in more than half of the world's countries and regions.In recent years,there have occurred many severe drought events in our country,which have a serious impact on agricultural production and human life,and have posed a serious threat to China's food security.Therefore,it is of important scientific significance to carry out researches on the spatio-temporal features of drought in the past 55 years and to master the law of drought occurrence and development.In this paper,the mean monthly precipitation and temperature data from 584 meteorological stations in China for the past 55 years are selected to analyze the spatial and temporal characteristics of the drought in China from1960 to 2014.The results show that:(1)On the national scale,from 1960 to 2014,the SPEI of China tended to decrease(-0.09/10a,R~2=0.272,P<0.001),and the trend of SPEI declines after 1996 was obvious.Fall SPEI declined was the most serious trend,followed by spring and summer,while the winter there was the phenomenon of humidification.Statistical analysis showed that the decreasing trend of SPEI in autumn,SPEI in spring and SPEI in summer were 0.11/10a,0.08/10a and 0.04/10a,respectively.On the site scale,the SPEI in 79.79%region of China tended to decrease,of which,22.95%of the regions had a significant decrease in SPEI.Stations with significant downward trend showed“Y”in spatial distribution,mainly distributed in Ningxia,northwestern Xinjiang,western Inner Mongolia,and northern Qinghai,and in some parts of Gansu Province and the southwest-northeast northeast of Inner Mongolia,Shaanxi,Shanxi,Yunnan,Chongqing and Sichuan.The areas where the SPEI in autumn,SPEI in spring and SPEI in summer decreased significantly accounted for25.51%,20.38%and 11.99%of the total in China respectively.(2)On the national scale,from 1960 to 2014,the total area of drought in China showed a significant increase(3.99%/10a,R~2=0.308,P<0.001),of which,the area of drought in China was close to or exceeded 20%after 1996.The spring drought area increased fastest(3.5%/10a)and the summer drought area increased slowest(2.7%/10a).Among them,the growth rates of arid areas above severe in spring and summer were1.5%/10a and 0.9%/10a,respectively.On the regional scale,the increasing rates of arid areas in arid,semi-arid,semi-humid and humid areas showed a decreasing trend,which were 6.57%/10a,3.78%/10a,2.86%/10a and 2.73%/10a,respectively.(3)On the national scale,drought frequency showed a significant increase in1960-1977,1978-1995 and 1996-2014.On the regional scale,The cumulative frequency of drought in arid,semi-arid,semi-humid,and humid areas showed a significant increase,especially in the past 20 years.On the site scale,njthe regions with the frequency of drought>20%in 1960-1977 were scattered in northwestern,southwestern and southeastern parts of China,while in 1978-1995 they were relatively concentrated in parts of northwestern and southwestern parts of China.From 1996 to 2014 drought frequency in most parts of our country exceeded 20%.Statistics showed that in 1960-1977,1978-1995and 1996-2014,the areas with drought frequency exceeding 20%accounted for 16.44%,19.35%and 78.42%of the total in China respectively.The frequency of drought in three periods of arid,semi-arid,semi-humid and humid areas further indicated that the frequency of drought in the past 20 years showed a significant increase.(4)The responses of vegetation changes to the changes of drought on longer time scales(above 6 months)were more obvious.The responses of different regions in different spatial distributions were also different,The spring was concentrated in the Bohai Rim region,the southwest region and the Beijing-Tianjin-Hebei region,summer in Tibet and the southwest region,and the maximum correlation value in autumn was concentrated in the agricultural-pastoral zone.And the effects of drought on different vegetation types were also different.The correlations between NDVI anomalies of different vegetation types and SPEI indicated that more than 40%of the significantly correlated regions corresponded to longer time scales(18 and 24).The responses of different vegetation types to SPEI at different scales had significantly differences in different seasons,and the grassland responded to drought is the most sensitive.