Assessment of climate change in terrestrial water storage over the Magdalena-Cauca basin

Terrestrial water storage (TWS) plays a key role in land-surface interaction and the hydrological cycle. Changes in the variability of its components, including surface storage, soil moisture and groundwater can lead to significant changes in local climate, water supply sources and agricultural production. In this study, we assess the impacts of climate variability and change in surface and subsurface hydrological variables over the Magdalena-Cauca basin (Colombia) using a distributed conceptual hydrological model (WMF) driven by precipitation and temperature from four GCMs (general circulation models). WMF is calibrated using daily precipitation products from the Tropical Rainfall Measuring Mission (TRMM). Monthly mean anomalies of surface and groundwater storage outputs show consistency with Gravity Recovery and Climate Experiment (GRACE) data. Past (1970-2001) and future (2021-2050 and 2071-2100) precipitation from GCMs are statistically downscaled using a quantile mapping method to a spatial resolution of 0.25 by 0.25 degrees.

Mean precipitation projections over the country are highly dependent on the selected GCMs, but the evidence shows agreement in a decrease towards the lower part of the basin; these projections are also present in surface runoff simulations. Annual mean streamflow follows the sign of the mean rainfall change over the basin. On the other hand, soil properties, topography, and geomorphological characteristics condition the patterns of subsurface and groundwater storage change (magnitude and localization), with the upper part of the Colombian Andes and the river mouth presenting the greatest changes. Results also show that mean soil moisture decrease in all scenarios, associated with changes in precipitation, but also due to the influence of temperature and evapotranspiration. The latter could lead to changes in the soil-atmosphere interaction, energetic conditions of the ecosystems and the need for agricultural mitigation strategies.