Drought characteristics in arid zone of middle Ningxia from 1960 to 2012 base on SPI index
With the purpose to provide scientific basis for regional agricultural development and disaster prevention and mitigation,by using the meteorological data from three in-situ stations during 1960 to 2012,the drought characteristics and variation trends in arid zone of middle Ningxia were studied by the method of standardized precipitation index (SPI),along with ensemble empirical mode decomposition (EEMD),power spectrum analysis and rescaled range analysis (R/S).The results showed that more than 30% of drought events,which happened in arid zone of middle Ningxia from 1960 to 2012,were moderate or even more serious drought.The multi-scale decomposition of drought period showed that there existed four time scales for the change cycle of different intensities of drought,i.e.,0.5 a for mild drought,1 a for moderate drought,3 a for severe drought,and 10 a for extreme drought.The EEMD analysis showed that the inter-annual fluctuation of drought was mainly derived from a 3.25-4 a period which contributed more than 65% to the whole variance,and followed by a 5.78-6.5 a period which contributed more than 14%.On the whole,the drought in arid zone of middle Ningxia is enhancing currently and this trend has a long-range dependence.Therefore,this region will keep a sustained drought in the future,but the characteristic of drought trend in various seasons is different.
droughtstandardized precipitation indexensemble empirical mode decompositionpower spectrum analysisarid zone of middle Ningxia