Study On The Regularity Of Drought And The Applicability Of Drought Index In Three Cities In Eastern Inner Mongolia

Drought is a kind of widespread natural disaster,which is the most frequent and result in serious social and economic losses in the world.Global warming not only leads to a significant increase in extreme drought?or precipitation?,but also leads to that some precipitation based on drought indicators may fail in these areas,such as the widely used Z index in China and the standardized precipitation index?SPI?recommended by the International Meteorological Organization.Under this background,the advantage of comprehensively considering the standardized precipitation evapotranspiration index?SPEI?of precipitation and many meteorological factors is increasingly obvious.However,SPEI has a higher requirement for meteorological parameters,and its important parameter reference crop evapotranspiration?ET₀?estimation formula has a lot of types.The eastern part of the Inner Mongolia has a strong sensitivity to climate change,being one of the regions with the most significant climate warming and meteorological disasters in China.In order to explore the applicability of precipitation-based drought indicators in the eastern part of Inner Mongolia in the context of climate warming,we verified the advantages of SPEI,which takes into account precipitation and many meteorological factors.This study used the daily meteorological data from 17 ground observation stations in 1961-2016 in the three cities of the Inner Mongolia Autonomous Region in Inner Mongolia,and the Z-index and SPI index were used to analyze the spatial-temporal evolution of drought in this area.On this basis,the ET₀ parameter was taken into consideration,and the difference between the ET₀ and precipitation-based drought index was analyzed using SPEI.At the same time,the three methods,i.e.Thornthwaite based on temperature,Priestley-Taylor based on solar radiation and Penman-Monteith integrated energy balance and aerodynamics were used to calculate ET₀.SPEI_PM was used as a criterion to analyze the advantages of drought index,drought duration,and drought intensity respectively.The applicability of Z index,SPI,SPEI_PT,and SPEI_TH in eastern Inner Mongolia was evaluated,and the main results are as follows:?1?In the premise that precipitation is the predominant driving factor of drought?temperature and ET₀ remain basically unchanged?,the Z-index of a single month time scale is too sensitive to individual extreme drought events,which has poor stability.Based on that SPI drought evolution overall trend has close relations with precipitation changes,we can comprehensively detect drought conditions at all sites,and different drought characteristics have great advantages to determine the reason of drought,therefore,SPI can more accurately reflect drought conditions in eastern Inner Mongolia than Z-index.?2?The temperature in eastern Inner Mongolia gradually increased from north to south,with an average temperature of 2.18?.In the past 56 years,the temperature of all stations showed a very significant upward trend?P<0.01?,with an average trend rate of 0.36?/10a.The ET₀ calculated by the Penman-Monteith,Priestley-Taylor,and Thornthwaite methods all decrease spatially with increasing altitude.The Daxing'an Mountains is the center zone,forming a low value region of ET₀,and the annual ET₀ decreases from southeast to north;In terms of time,although the mean ET₀ values are different,the trend rates of the three indicate that the ET₀ in the eastern Inner Mongolia region shows a rising or a significant rising trend,indicating that the precipitation-based drought index should not be directly applied in the region.?3?Using SPEI_PM as the standard,the calculation results of SPI,SPEI_PT,and SPEI_TH,are compared and analyzed.At different time scales,SPEI_PT and SPEI_PM have the highest agreement with the detection and assessment results of drought frequency,drought duration,and drought intensity of drought events.Therefore,in the eastern part of Inner Mongolia,SPEI_PT is recommended instead of SPEI_PM,which not only reduces the accuracy of meteorological parameters,but also greatly reduces the complexity of SPEI calculation.If only temperature and precipitation data are available,SPEI_PT and SPI have differences in the accuracy of drought detection at different time scales.When the time scale is less than 8 months,SPEI_TH is recommended.When the time scale is greater than or equal to 8 months,SPI is more reasonable.Because in the context of climate warming,although SPI index can describe the trend of drought,the effect of evaporation on drought is neglected,and it is not suitable to describe the trend of drought in Inner Mongolia.The SPEI_TH ignores the effect of evaporation below 0?when calculating the ET₀ using the computed Thornthwaite method,resulting in a certain degree of error.