Numerical Diagnosis And Simulation Of Soil Moisture Influences On Air Temperature In China

Extreme high temperature events occur frequently with the global warming,which have a significant impact on human production,life,social and economic development.More and more scholars are beginning to pay attention to the physical mechanism behind extreme high temperature events.Land-atmosphere interactions contain important material and energy exchange processes,which can significantly affect the occurrence of extreme high temperature events.Soil moisture is a key factor in land surface processes,and its small-scale physical process of the effect on atmosphere considered as a strengthening mechanism that may cause temperature anomalies.Current research methods for land-atmosphere interactions are mainly based on numerical diagnosis and model simulation.However,the limited insitu soil moisture cannot meet the research needs,and the model also pays less attention to the impact of soil moisture anomalies on extreme events.In this paper,China was selected as the research area.Firstly,we used the currently widely used ERA-Interim dataset to describe the spatial and temporal distribution of soil moisture in China.After a certain understanding of the climatic characteristics of it,then we utilized the statistical diagnostic method to study the soil moisture-temperature coupling in China from 1980-2013,exploring the soil moisture-temperature coupling hot spots as well as the variation of coupling intensity in different seasons and regions,and tried to find the relation between soil moisture and heatwaves.Finally we used regional climate model of Reg CM4.7 to design temperature sensitivity test from 1979-2015 in China,analyzing how soil moisture anomalies affect the frequency and intensity of extreme high temperature in different regions.The main research results are as follows:(1)The annual and seasonal average spatial distribution of soil moisture in China is characterized by an increasing from northwest China to northeast China and south China.Different typical climate regions have different tendency of soil moisture drying,which is most obvious in humid regions,followed by transition regions.The inter-monthly variation of soil moisture in humid area and transition area is large,while in arid area and Tibet Plateau is small.(2)Hot spots of soil moisture–temperature coupling were found in North China and over the Tibetan Plateau,indicating that the soil moisture–temperature coupling is strongest in the transitional climate zones.Soil moisture-temperature coupling is relatively strong in spring and seasonality of coupling strength has marked regional variation.From the case study of the 2013 Southeast China heatwave and the 2009 North China heatwave,it was found that enhanced heat and temperature anomalies associated with soil moisture deficit,resulting in enhanced soil moisture–temperature coupling.(3)RegCM4.7 was used to simulate the air temperature in China,results showed that the model can better simulate the spatial distribution of the annual mean of temperature,and the high,low temperature areas and some special terrain areas can also be well described.Changes in soil moisture can explain over 40% of the variation in the frequency and intensity of extreme high temperature in humid region and transitional region during the summer.The influence of soil moisture anomalies on air temperature varies in typical climatic regions.In arid zone,soil moisture anomalies had a certain effect on the frequency and intensity of extreme high temperature,but it is not very significant.In the transitional zone,dry soil moisture increased the frequency and intensity of extreme high temperature by 40% in most areas,while moist soil moisture reduced the frequency by 40% in most areas.The response of extreme high temperature in the humid area is very sensitive to the negative anomaly of soil moisture which can cause the frequency of extreme high temperature in the humid area increasing by 60% and the intensity increasing by more than 40%.However,the impact of extreme high temperature on the soil moisture wet years is not so significant.In the Tibet Plateau region,the negative and positive anomalies of soil moisture have similar effects on the frequency and intensity of extreme high temperature,which also reflects the frequency and intensity of extreme high temperature in the western part of the Tibet Plateau decreasing,while the frequency and intensity of extreme high temperature in the eastern part increasing.