Atmospheric moisture exchanges between the Magdalena River basin and its surroundings.

Atmospheric moisture transport is a fundamental process in the climate system, critical for the hydrological cycle and water security on land. Moisture exchanges between a basin and its surroundings determine water availability and may change over time due to climate change and other human impacts. Understanding how and why these atmospheric fluxes change under global change is critical for river basins supporting water security in different regions. Here we focused on the Magdalena River basin in northwestern South America, a critical basin for water and energy security in Colombia. We quantified moisture exchanges for the entire watershed and different segments (defined by the boundaries between neighboring basins). We used monthly data between 1979 and 2021 from the ERA5 reanalysis to look for possible changes, including trends. Our results provide new insights into the dynamics of moisture exchanges between the basin and its surroundings. In addition, we found evidence of statistically significant trends likely related to anthropic effects, mainly deforestation and climate change. These results have implications for water security analyses in this region, where there are few studies of this type, and simultaneously generate new insights for decision-making related to water management and transboundary water security in the Magdalena river basin.