Temporal And Spatial Variation Characteristics Of Air Temperature And Precipitation And The Applicability Of Reanalysis Data In Pakistan

The climate environment of Pakistan is fragile and sensitive to global warming,so it is of great significance to analyze and predict its climate change.Based on the air temperature data and GPCC precipitation data from Pakistan meteorological stations,combined with CRU,ERA-5 and MERRA2,the spatial and temporal variation characteristics of air temperature and precipitation were analyzed at interdecadal,annual and seasonal scales,and the applicability of reanalysis data to represent the air temperature and precipitation changes in Pakistan was evaluated.At the same time,the air temperature and precipitation data of Gwadar Port and its surrounding stations were selected for comparative analysis to obtain the characteristics of air temperature and precipitation in Gwadar Port.The results as below:Pakistan showed a warming trend during 1960-2019.The annual,spring,summer,autumn and winter air temperatures began to increase in the 2000 s,2000s,1990 s,1980s and1990 s,and the warming rates were 0.185,0.35,0.099,0.19 and 0.145 ?/10 a respectively,with the most obvious increase in spring.There was no abrupt change of annual and autumn temperature in Pakistan during the study period.The abrupt change points of spring,summer and winter temperature were located in 2000,2006 and 1987,and the quasi-change periods of annual,spring,summer,autumn and winter temperature were 12,12,20,16 and 19 years,respectively.The air temperature was higher in the south and lower in the north,which in the Indus Plain and delta region is relatively high,followed by the western Baluchistan Plateau,and the northern mountainous region is relatively low.Most of the regions show a warming trend,and the warming rate is the largest in the southern high air temperature region.The mean annual precipitation in Pakistan from 1980 to 2016 is 430.4 mm,concentrated in July and August.The variation trend of precipitation was random stationary-weakening,and the annual mean precipitation decreased by-3.898 mm/10 a.The variation rates of precipitation in spring,summer,autumn and winter were-5.8,-1.1,6.69 and-3.68 mm/10 a respectively.The abrupt changes of annual,spring,summer,autumn and winter precipitation in Pakistan occurred in 1997,1987,2003,2009 and 1986,and there were 22,8,19,11 and 22 years of leveling change cycles.The spatial pattern of precipitation was "low in the south and high in the north",mainly concentrated in the north and northeast of Pakistan.In the past 37 years,the precipitation at the Indus River Plain increased,while the precipitation at the western Baluchistan Plateau decreased.From 2018 to 2019,the mean annual air temperature at Gwadar Port is 26.9 ?,and the annual and daily air temperature range were 12.5 ? and 6.5 ? respectively.The precipitation in Gwadar Port is unevenly distributed between year and season,the precipitation in 2018 is 0.3 mm,and in 2019 is 67.6 mm.Moreover,it is affected by westerly wind disturbance,and most of it is concentrated in winter.When ERA-5,MERRA-2 and CRU data were used to characterize the temporal and spatial variation characteristics of air temperature in Pakistan,the performance of CRU and ERA-5 data was better than MERRA2 data.Accuracy evaluation of CRU data performed better in year,summer,autumn and winter,and ERA-5 data had better applicability in spring.When used to characterize the spatiotemporal variation characteristics of precipitation in Pakistan,the error between CRU data and observation data is small and the degree of fitting is good,while ERA-5 and MERRA2 data and observation data have large error and weak correlation.