Spatial And Temporal Variation Of Droughts Over China Based In Various Potential Evaptranspiration Formulas

In the context of global warming,the rate of water cycle is accelerated and extreme drought and waterlogging events occur frequently,which have an increasing impact on human society,economy and crop growth.Therefore,drought assessment has an important demand for mitigating and coping with the impact of drought.In this article,eight kinds of potential evaporation formulas(P-M,Penman,Energy-Only,Priestley-Taylor,Hamon,Oudin,Hargreaves and Samani and Thornthwaite)are divided into three categories by their driving factors(synthesis models,radiation-based models and temperature-based models).Based on ground meteorological observation data,compared the difference between the results for different potential evaporation formulas.Standardized precipitation evapotranspiration index(SPEI)is used to analyze the evolution characteristics of drought intensity,coverage,frequency and duration in different climate zones of China since the 1960s.Combined with drought affected areas,the adaptability of eight potential evaporation methods in different areas of China are achieved.The evolution and uncertainty by different kinds of potential evaporation formulas for droughts in China under global warming of 1.5? and 2.0? scenarios can be quantitatively assessed through the simulation ensemble of 5 global climate models.(1)During 1961-2017,the gaps of the results for different potential evapotranspiration methods were nearly 2.5 folds.The annual PET(potential evapotranspiration)of Penman synthesis method was the highest,and the temperature-based methods that just consider about the effects of temperature were relatively lower.The eight SPEI indices differed significantly in arid region,with an increasing SPEIP-M trend,while the SPEIPriestley-Taylor and four temperature-based methods showed a drying trend.But in semi-arid and semi-humid region as well as humid region,the SPEI sequence fluctuations were relatively consistent.The spatial distribution of the northeast-southwest drought zone was reflected in all the eight algorithms.The drought duration increased from southeast to northwest.However,the estimation of drought frequency by radiation methods and temperature methods are larger than that by comprehensive method,and the duration of drought estimated by synthesis methods are longer.Compared with observation of drought affected area,eight methods can be used for assessment of drought assessment in humid region,semi-arid region and semi-humid region.However,SPEIP-M has the best correlation with affected area in arid region.P-M method is more applicable in this region and radiation-based methods behaves relatively worst.(2)Under the 1.5? global warming scenario,eight types of potential evaporation will all on the rise with the growth of around 5%in humid region compared with 1986-2005,strongest increasing by temperature-based methods and weakest by radiation-based methods.Drought intensity will increase relatively to 1986-2005,with a strongest increase of about 6%in arid region.Drought frequency decreased about 12%compared with 1986-2005 in arid region,but it will increase in semi-arid and semi-humid region as well as humid region.Drought duration at a time will increase significantly in arid region,which will be about 1.9 times as long as in 1986-2005.In the semi-arid and semi-humid region,the duration will last about 7.6(7.1?8.8)months every time that prolong nearly 2 months,and drought duration will be about 0.4 months longer than baseline period in humid region.(3)In the 2.0? global warming level,annual PET will increase and temperature-based methods with the fastest growth rate.The growth rate in humid region may reach above 10%.The intensity of drought will increase by more than 25%in the arid regions and by more than 15%in the central and western parts of the semi-arid and semi-humid region.In the arid region,the drought frequency will decrease from 11.8 times in the baseline period to 8.8 times(6.3?10.5),while it will increase by about 14%in the semi-arid and semi-humid region.Beside,a significantly increasing belt of drought frequency will appear in the transition zone between the semi-arid and semi-humid region as well as the humid region,with an increase of about 30?40%.Drought duration will show an increasing trend,with the increase of about 2.5 times in the arid region up to 18 months(11-25.4 months),while the increase will be not significant in humid region,mainly concentrated in the southwest and central of the humid region.(4)Temperature-based methods are more sensitive to warming along with synthesis method and radiation-based methods.Global warming of 2.0? compared with warming of 1.5?,annual PET will increase.Drought intensity will increase in different regions,among which the majority of arid region will increase by more than 10%.While the variation of drought intensity will be relatively slight in semi-arid and semi-humid region as well as humid region.Drought frequency will decrease and obviously in arid region.But drought frequency will increase significantly in transition zone of semi-arid and semi-humid region as well as humid area and northeast of semi-arid and semi-humid region.Drought duration will be extended 5 months in arid region and decrease in southwest of semi-arid and semi-humid region.The projection of drought is of great significant for people to cope with climate change and disaster prevention and mitigation.Compared with warming of 2.0?,under the scenario that global warming rate is controlled within 1.5? before industrialization,the impact of drought on people's life and economic development can be effectively mitigated.