Temporal and spatial analysis of drought for recent 50 years in Loess Plateau of Gansu province based on meteorological drought composite index

Drought,one of the most severe hazards resulting in significant economic loses in agriculture and industry,is a natural phenomenon caused by the imbalance between import and demand for moisture.In the context of global climate change,the drought intensity,frequency,and its spatial patterns have been changing.In this paper,based on ArcGIS9.3 and SPSS software platform,the observed meteorological data of 33 meteorological stations from1962 to 2010 in Loess Plateau of Gansu province of China were collected and a composite index(CI) of meteorological drought was used to analyze the temporal and spatial characteristics of drought in the area.Firstly,the historical day-to-day CI was calculated,and on the basis of the statistics on drought events in each station and each stage in recent 50 years,coverage area of drought in each station,the occurrence frequency and scope were computed and analyzed to reveal the temporal and spatial occurrence pattern of the meteorological droughts in different parts of Loess Plateau of Gansu province.The results were showed as follows.(1) The large area drought in whole Loess Plateau of Gansu province occurred mostly in summer and autumn but least in winter during the period of 1962 to 2010.(2) In view from space scale,The highest zone in Loess Plateau of Gansu province is in Lanzhou-Jingyuan region and the northern part of Qingyang region.but the lower zone is Minxian-Weiyuan region.Meanwhile,in Lintao-Tongwei-Tianshui region and the south-eastern part of Qingyang region,the change range is the largest.(3) In summer,The annual and seasonal occurrence frequencies of the meteorological drought and lasting days of different grades in Loess Plateau of Gansu province was most,in winter,it is least.