| Based on GLDAS NOAH soil moisture data and CPC precipitation data,the temporal and spatial distribution of soil moisture and precipitation on the Qinghai-Tibet Plateau from 1979 to 2018 and their correlations have been analyzed.Numerical experiments are designed to simulate and sensitize one case of precipitation in the eastern part of the Qinghai-Tibet Plateau from August 6-9,2014,and explore the mechanism of the effect of soil moisture on precipitation.The results show that:(1)In the past 40 years,the distribution of soil moisture in the Qinghai Tibet Plateau is characterized by low in the north and high in the south,while the distribution of precipitation is characterized by low in the north and high in the south?low in the West and high in the East.The soil moisture in the central and eastern Qinghai-Tibet Plateau is mainly increased,and the western region is mainly reduced.The precipitation in the Ali and Linzhi regions of the Qinghai-Tibet Plateau is mainly reduced,while the precipitation in the central and high-altitude areas of Qinghai and Tibet is mainly increased.(2)In the past 40 years,the changes in soil moisture and precipitation in the various layers of the Qinghai-Tibet Plateau are relatively consistent,and the overall trend of soil moisture and precipitation is increasing.The annual change range of soil moisture in 0-10 cm layer is the largest,and it is similar to that of precipitation.(3)The soil moisture of the Qinghai-Tibet Plateau is generated by EEMD decomposition in four component cycles,which are 4.1 years,8.3 years,15.6 years,and 32.2 years respectively.Precipitation through EEMD decomposition generates four component periods,which are 3.6 years,9.3 years,20.2 years,and 32.1 years respectively.In the past 40 years,both soil moisture and precipitation have shown a "decline-rise" trend,and precipitation has lagged behind soil moisture characteristics.(4)In terms of spatial distribution,inter-annual variation,and intra-annual variation,there is a significant correlation between soil moisture and precipitation on the Qinghai-Tibet Plateau.But as soil depth increases,the correlation coefficient gradually decreases.The previous precipitation mainly has a positive correlation effect on soil moisture;the early soil humidity has a positive correlation effect on precipitation within 20 days,and a negative correlation effect on 50-120 days.(5)The control test can better simulate the spatial distribution and change trend of the precipitation.The TS score indicates that the control test is good for simulating precipitation of small to moderate rainfall and of large to heavy rainfall,which can be used as an effective control test to compare with the sensitivity test.(6)Sensitivity tests indicates that during the daytime,the feedback mechanisms of soil moisture and precipitation are mainly negative,and increasing soil moisture will reduce daytime precipitation;at night,the feedback mechanisms of soil moisture and precipitation are mainly positive,and increasing soil moisture will increase nighttime precipitation.And the more the soil moisture increases,the greater the change in precipitation.(7)With the increase of soil moisture in the Qinghai-Tibet Plateau,the soil heat capacity increases,making the surface temperature increase and decrease slowly,which in turn affects convective precipitation through thermal effects.The increase of soil moisture reduces the surface temperature during the day,reduces the surface sensible heat flux,reduces the surface heating atmosphere,reduces the unstable energy in the troposphere,which is not conducive to the strengthening of vertical airflow,and reduces the intensity of low-level convergence and high-level divergence,also convective strength.It produces a negative feedback effect,which reduces precipitation during the day;and the opposite mechanism at night and day forms a positive feedback effect,which increases the precipitation at night. |
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