Calibration and Validation of a SWAT model for the quantification of water provision ecosystem service for the Conservation Area of Guanacaste

Abstract

Water is considered a cross -cutting resource for all the ecosystem services (ES) types, namely: for the provision of drinking water and food; regulation through flood control; guarantee of a suitable habitat for fauna and flora; and inspiration for many cultures and their intangible heritage around the planet. The evaluation of water ecosystem services has drawn much attention both in the political arena and the scientific community. Still, there is not a consensus in the approach of evaluating them. Recent notions suggest that the study of ES cannot be assessed from a single discourse but through comprehensive frameworks. Therefore, the main objective of this thesis was to evaluate the water provision as an ecosystem service of the Conservation Area of Guanacaste (ACG, for its acronym in Spanish) by adapting an Ecosystem Services (ES) -based approach with four core elements: (1) effects on human well -being, (2) bio-physical underpinning of service delivery, (3) transdisciplinarity, and (4) assessment of services for decision- making. I have deepened in core element two by assessing all the physically -based processes involved in the hydrologic cycle, which generates the quantity of water available for the study region. As a result, here I present the first calibrated and validated Soil and Water Assessment Tool (SWAT) for the entire ACG, including the land use and cover change (LUCC) impact on water availability. I tested seven different climatic and geospatial information resources to establish the best input data to build the SWAT model . The model showed excellent performance for both the calibration period ( r2 = 0.81, NSE = 0.75, and br2 = 0.80) and validation period ( r2 = 0.85, NSE = 0.82, and br2 = 0.85). I have found that the ACG has a high potential for the provision of water as an ecosystem service. I also identified the spatial and temporal patterns and changes in the water availability in this region between 1980 - 2019. I deepened in the vegetation -water dynamic understanding by evaluating the land use cover change (LUCC), finding that the recovery of forests, and decrease in grasslands and agricultural territories have a positive effect on the water availability also associated with exceptional events in Costa Rica’s history that put in place the conditions for the recovery of natural resources. I also demonstrated the advantages of using spatially explicit and physically-based models, such as SWAT, to quantify water provision as an ecosystem service. Finally, this work complements the baseline for future applications of ES-based approaches in this region.