Drought characteristics in Ningxia based on standardized precipitation index
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Abstract:
Under the background of global warming,drought has become the foremost disaster endangering agricultural and animal husbandry production,thus it has an increasingly negative impact on human life.Ningxia is in the arid and semiarid area,and has limited water resources and fragile ecology due to its unique climate.At present,studies on drought are mainly conducted in southwest China,the Yangtze River and Yellow River basins,and many provinces in China,while few in Ningxia,which has been threatened by water shortage and drought for decades.Therefore,it is of great significance to clarify the spatiotemporal variation characteristics of drought in Ningxia. The standardized precipitation index (SPI) was used as the drought index,and the drought frequency and the drought intensity were used to evaluate the drought characteristics.Based on the distribution probability of precipitation during a certain period,SPI carries out the normal standardization processing.Then,the cumulative frequency distribution of standardized precipitation is used to divide the drought grade of the northern Yellow River irrigation area,the central arid zone and the southern mountainous area.The drought frequency is the frequency of drought occurring during the study period,while the drought intensity is an important index to evaluate the severity of drought.The drought frequency and the drought intensity were analyzed and evaluated at seasonal and annual scales in each study area of Ningxia. The results show that the variation trend of temperature and rainfall of different regions in spring,summer,autumn,and winter from 1960 to 2016 is almost the same;the interannual variation difference of temperature is not obvious,the distribution of temperature is not uniform,but the overall trend of warming and drying appears.In the autumn of 2004,a drought event happened in the Yellow River irrigation area,where the SPI index reached 243 and the frequency is 172%;in the winter of 1998,a drought event happened in the arid zone,where the SPI is 298 and the frequency is 1.72%.In the spring of 1994,the summer of 1981,the 1971,the autumn of 1985,and the winter of 1998,drought events happened in the southern mountain area,with the SPI value of 2.17,2.11,2.61,220,3.25,and the frequency of occurrence of 77.59%,10.34%,5.17%,5.17% and 1.72%,respectively.For the SPI in the regional scale during the study period,the count of excessive drought events in the Yellow River irrigation area,the arid zone and the southern mountainous area increased.For the SPI value in the time scale,the frequency of excessive drought events decreased in recent years.According to the analysis and calculation of the annual and quarterly drought intensity in each region,the annual drought intensity fluctuated between 0.68 and 1.47.The times of drought intensity greater than 0.5 were 28,29,and 27 times,respectively;the average drought occurred in 2.07 years,2 years,and 2.1 years.From the perspective of seasonal scale,there are certain differences in different regions and different seasons. The spatial and temporal distribution of rainfall and temperature in Ningxia was uneven and the interannual difference was obvious.The annual rainfall had a significant decreasing trend;the seasonal rainfall had an overall decreasing trend but a rising trend in winter and autumn of the irrigated area along the Yellow River.The average annual temperature and seasonal temperature showed an increasing trend.The annual drought was more frequent and lasted longer in the northern Yellow River irrigation area,the central arid zone,and the southern mountainous area;the drought intensity showed a decreasing trend.The years with the highest intensity were 2004,1981,and 1981,respectively.In the three regions,the seasonal scale drought showed a decreasing trend in summer,autumn of the arid zone and southern mountainous area,while the rest showed an increasing trend.The decreasing degree of drought in summer and autumn was attributed to the fact that most of the rainfall was concentrated in summer and autumn,and the rainfall frequency was more frequent in recent years.The seasons with the greatest drought intensity in the three regions were the summer of 2007,spring of 1994,and winter of 1998.
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