Atmospheric moisture exchanges between the Magdalena River basin and its surroundings

Abstract

ABSTRACT : Atmospheric moisture exchanges between river basins and their surrounding areas are vital to the global climate system and the hydrological cycle. In this study, we aimed to characterize the exchanges of atmospheric moisture between the Magdalena River basin (Magdalena Basin) and its surroundings, focusing on identifying change signals and their implications for water security in Colombia. We utilized monthly vertically integrated eastward and northward fluxes of water vapor, cloud liquid water, and cloud frozen water from ERA5 to estimate the atmospheric moisture fluxes over the Magdalena Basin and each of its frontiers with surrounding basins and the oceans from 1962 to 2021. We used seasonal and trend decomposition using LOESS, Theil–Sen slopes, and Mann–Kendall tests to assess the trends in the monthly series. We performed similar analyses for the discharge data series from IDEAM. Our results show that atmospheric moisture fluxes around the Magdalena River basin exhibit predominant directions, with moisture inflow primarily originating from the East (in the East Caribbean, Orinoco basin, and Amazon basin frontiers) and outflow occurring predominantly toward the West (in the West Caribbean and Pacific frontiers). Furthermore, we found that atmospheric moisture fluxes exhibit temporal persistence in their annual cycle for each basin frontier studied, with inflows exhibiting a predominant tendency to remain as inflows and outflows showing a dominant tendency to stay as outflows. We identified statistically significant trends across the entire dataset. We observed increasing trends for the atmospheric moisture in the eastern basin frontiers (the Amazon, Orinoco, and Eastern Caribbean frontiers) as well as for the entire basin and decreasing trends for the atmospheric moisture in the western basin frontiers (Pacific and Western Caribbean) as well as for the river discharge series. The trend slopes were +4.48, +10.75, +1.96, +1.96, -9.07, -6.91, and -0.53 (m3/s)/month for Amazon, Orinoco, Eastern Caribbean, the entire basin, Pacific, Western Caribbean atmospheric moisture, and the Magdalena River discharge, respectively. Our study also found that ENSO phases affect the intensity of the fluxes, which increase during La Niña and decrease during El Niño events. The influence of ENSO on Colombia's hydrology and the Magdalena Basin illustrates how changes in moisture fluxes can sensibly affect the country's water and energy security. The identified changes in atmospheric moisture exchanges between the Magdalena Basin and its surroundings have significant implications for water security in Colombia, particularly in the ongoing environmental and climatic changes. The observed increasing trends in atmospheric moisture in the eastern basin frontiers and the entire basin suggest that the Magdalena Basin may experience more precipitation and water availability. However, the decreasing trends in atmospheric moisture in the western basin frontiers and the river discharge series indicate potential water scarcity and droughts in these regions. Additionally, our results revealed an imbalance between the inflows and outflows in the Magdalena River basin, which should be the subject of further study. This imbalance is hypothesized to be due not only to uncertainties in the data but also to potential long-term changes in basin storage, as observed in other large basins around the world. Our study contributes to a deeper understanding of atmospheric moisture dynamics in the region and supports better-informed decision-making in water management and adaptation to climate change. The identified change signals in atmospheric moisture exchanges can inform policymakers and water managers in Colombia to develop effective strategies to mitigate the potential impacts of water scarcity and droughts in the western basin frontiers. Additionally, our study highlights the importance of understanding the physical mechanisms underlying the identified changes to better predict any future changes in atmospheric moisture exchanges and their implications for water security in Colombia.