A Study of the Dependence between Soil Moisture and Precipitation in different Ecoregions of the Northern Hemisphere

Abstract. Soil moisture plays a critical role in the land–atmosphere coupling system. It is replenished by precipitation and transported back to the atmosphere through land surface evaporation and vegetation transpiration. Soil moisture is, therefore, influenced by both precipitation and evapotranspiration, with spatial heterogeneities and seasonal variations across different ecological zones. However, the effects of precipitation volume, frequency, and evapotranspiration on soil moisture at different temporal scales still remain poorly understood. Negative correlations between soil moisture and precipitation have been observed in different ecosystems of the Northern Hemisphere. In this study, the response of soil moisture to precipitation from 2000 to 2019 was investigated using reanalysis data to determine the factors driving the negative correlations. The joint distributions of precipitation and soil moisture were analyzed at monthly and annual scales, using soil moisture and precipitation data from ERA5-Land and Global Precipitation Climatology Project, respectively. Nonlinear negative dependencies of soil moisture to precipitation were revealed. Based on Ridge regression models and Bayesian generalized non-linear multivariate multilevel models, these negative dependencies were shown to be most prominent in temperate grasslands, savannas, shrublands, deserts, xeric shrublands, and tundra regions and driven by the land surface temperature and by the air temperature–gross primary production relationship at the monthly scale. Additionally, the negative dependence was attributed to soil property changes induced by freeze–thaw processes, precipitation seasonality, and temperature fluctuations, which cause asynchronous variations between soil moisture and precipitation at the seasonal scale. At the annual scale, the negative dependence was linked to long-term shifts in global precipitation and temperature patterns, which affect vegetation structure and surface characteristics, thereby reducing soil water capacity. These findings enhance the understanding of land–atmosphere interactions providing a valuable basis for future research on drought, hydrometeorology, and ecological conservation.