Satellite-based re-examination of global soil moisture variation

Abstract

It was crucial to capture the variation in global soil moisture for exploring the global eco-hydrological processes. Based on the global soil moisture data from the Climate Change Initiative (CCI) published by the European Space Agency (ESA), this study re-examined the spatial pattern and temporal trend of global soil moisture from 1978 to 2021. Our results showed that the global mean soil moisture was 0.208 cm³·cm⁻³, which showed a weak decreasing trend over the past four decades (−1.2 × 10^-4 cm³·cm⁻³ yr⁻¹, R² = 0.23, p = 0.001). Spatially, about 12.99 % of the land showed a significant drying trend, while only 6.74 % of the land showed a wetting trend. However, in the last decade, global soil moisture exhibited a distinct upward trend (7 × 10^-4 cm³·cm⁻³ yr⁻¹, R² = 0.87, p = 0.000). Specifically, during this period, 5.72 % of the land showed a marked drying tendency, while 9.09 % of the land displayed a wetting trend. Soil moisture variation in the arid climate zones showed a negative contribution to the global trend, with the total contribution of −45.72 %. In contrast, soil moisture trends in temperate and cold climate zones mainly exerted positive contributions to the global trend. From a continental perspective, Asia’s positive contribution was the most significant, accounting for 39.96 %, whereas North America showed a significant negative contribution of −37.43 %. Temporally, the negative maximum change in soil moisture occurs in June-August and the positive maximum change occurs in September-November, serving as the predominant d river for the annual trend. Results of this study helped to clarify the variation of global soil moisture, which could support the sustainable water management in the changing climate.