Study On The Spatiotemporal Coupling Of Soil Moisture And Afternoon Precipitation In The Qinghai-Tibet Platea

Soil moisture is an important factor in land-atmosphere interactions,and its relationship with precipitation is complex.Due to differences in datasets,research methods,and analysis scales,soil moisture-precipitation coupling relationship is still controversial and required further investigation.Previous studies have mostly focused on the effect of soil moisture on precipitation in the Tibetan Plateau over large-scale spatial and temporal scales,and little attention has been paid to the effect of soil moisture on afternoon local convective precipitation at the daily scale.In this study,we firstly evaluated accuracy and consistency of three gridded soil moisture datasets over the plateau,and analyzed the spatiotemporal characteristics of soil moisture and land-atmosphere coupling over the plateau during the warm season.Secondly,utilizing a probability-based method,the temporal and spatial soil moisture-precipitation couplings were analyzed.Finally,we analyzed the response of key variables characterizing land-atmosphere coupling to soil moisture anomalies to reveal the influence of soil moisture on precipitation.The main conclusions of this study are as follows:(1)Based on the evaluation of observation data,ERA5 and GLDAS overestimate soil moisture on the plateau,while the accuracy of SMAP is high.Based on the Triple Collocation method,SMAP exhibits the smallest random error over the plateau and the highest temporal correlation with the unknown true SM in the eastern plateau.ERA5 has a better temporal correlation with soil moisture true values in the western plateau,which is consistent with the evaluation results based on observation data.Soil moisture on the plateau gradually decreases from southeast to northwest,and the variability of soil moisture variability is the largest in the southwestern plateau.Low-frequency(30–90 days)variations are the largest contributor to intraseasonal variability of soil moisture.Relative to SMAP,the contribution of high-frequency variations is low in ERA5 and GLDAS.Land-atmosphere coupling is stronger(weaker)in the western(southeastern)plateau,which is relatively dry(wet).Land-atmosphere coupling in the western plateau is the strongest in July.(2)The magnitude and sign of soil moisture and afternoon precipitation spatiotemporal couplings is investigated using a probability-based approach.Satellite data shows that the temporal coupling between soil moisture and afternoon precipitation over the plateau is mainly positive,that is,afternoon precipitation in most areas of the plateau tends to occur on patches when soil moisture is wetter than the climate state.ERA5 reanalysis data shows that the temporal coupling in the western plateau is mainly positive,while in the eastern plateau,it is mainly negative.Satellite and ERA5 consistently indicate that the spatial coupling between soil moisture and afternoon precipitation over the plateau is mainly positive,that is,afternoon precipitation in most areas of the plateau tends to occur on patches when soil moisture is wetter than the surroundings.The correlations of the temporal and spatial coupling in satellite data are higher than that of and ERA5 reanalysis.The lower coupling signal in ERA5 may be related to its overestimation of soil moisture,which influences the related land-atmosphere interactions.(3)By analyzing the response of key variables characterizing land-atmosphere coupling to soil moisture spatiotemporal anomalies before events,it was found that soil moisture comprehensively affects the distribution of surface heat fluxes and the evolution of atmospheric boundary layers in time and space,thus affecting afternoon convective precipitation.In terms of time,the soil moisture in the western plateau mainly humidifies the boundary layer,while the soil moisture in the eastern plateau mainly heats the boundary layer.In terms of space,the soil moisture heterogeneity on the plateau mainly humidifies the boundary layer.