Variability and change of large-scale soil moisture in tropical catchments: data-model comparison and future change scenarios

Abstract:

Soil moisture is a key aspect of ecohydrology, at the heart of essential processes in water balance and cycling, climate change, and both ecosystem and societal conditions, not least important for the agricultural and water management sectors. This paper presents a relatively simple mechanistically based model for screening temporal variability and change of large-scale soil moisture. The model ability to reproduce long-term data series of large-scale subsurface water storage change, as sensed by the GRACE satellite, is investigated for multiple large tropical catchments around the world. The paper further investigates how future hydro-climatic changes may affect various soil moisture aspects and temporal statistics in these catchments. The considered future hydro-climatic changes in the catchments are from 2006-2025 to 2080-2099, as projected by 14 of the latest generation (CMIP5) global climate models for different radiative forcing (RCP) scenarios. The comparison with GRACE data shows good model ability to reproduce observed temporal variability statistics of large-scale water-storage changes in the tropical catchments. Regarding future conditions, relatively large changes are projected to occur until the end of this century in the inter-annual variability (coefficient of variation) of seasonal soil water content over the unsaturated zone, regardless of considered RCP scenario. Especially for water content in the dry season, large increases in inter-annual variability emerge for several of tropical study catchments. Precisely which catchments may be expected to experience the greatest changes, however, depends on the considered RCP scenario.