Influence of South America Tropical Deforestation and El Niño-induced Alterations on Terrestrial Moisture Recycling Related with Transboundary Water Security of Antioquia

Abstract

ABSTRACT : Terrestrial moisture recycling (TMR) establishes transboundary links between river basins and countries worldwide, especially in regions where precipitation depends highly on terrestrial sources of atmospheric moisture through evapotranspiration. Tropical South America, particularly Colombia and its Antioquia Department, are among such regions, partly due to the role of the Amazon forest in distributing water throughout South America. This doctoral dissertation seeks to understand better the TMR's role in linking river basins and countries, with implications for water security in our study region and globally. The dissertation is organized into five chapters corresponding to five scientific papers that are already published (two papers) or are in preparation (three papers). First, we used a metaanalysis to investigate the effect of including or excluding TMR in modeling studies about deforestation's effects on river flow. Results indicate that neglecting transboundary effects and deforestation impacts on precipitation ---which is the most widely used approach--- leads to the potentially misleading conclusion that deforestation increases river discharge of large basins. Second, we used regional climate model simulations to test the hypothesis that the Amazon forest enhances precipitation along wind streamlines passing over it and that deforestation can disrupt this pattern. Results support this hypothesis and suggest the existence of a deforestation tipping point beyond which the exponential growth of precipitation will reverse into an exponential decrease. Third, we used tracking-moisture model simulations to study the global impacts of El Niño on TMR. Results show that in seven regions around the globe, El Niño impacts on TMR contribute to explaining precipitation anomalies, which is a previously-overlooked mechanism through which El Niño affects precipitation worldwide. Fourth, we used reanalysis data to describe the most important precipitationshed (MIP) of the Magdalena River basin, including its seasonal and inter-annual dynamics while considering the El Niño and La Niña impacts. Results show that the Magdalena basin in Colombia is significantly dependent on atmospheric water originating in the Orinoco and Amazon river basins and neighboring countries, posing challenges to water management in the Magdalena basin that is critically important for water and energy supply in Colombia. Further, results show that the Magdalena's MIP varies with El Niño and La Niña, providing new insights into the mechanisms behind the pronounced ENSO impacts on precipitation in Colombia. Fifth, we applied two risk assessment frameworks to test the hypothesis that accounting for upwind moisture flows considerably increases risks to transboundary water security in basins that are important for agriculture and food production worldwide. Results support this hypothesis, highlighting the need to incorporate atmospheric water and transboundary linkages into water security and risk assessments. Finally, although each chapter includes specific conclusions, we present general conclusions in chapter six.