Capturing Forest Dynamics in Hydrological Modeling

Abstract

Forests can cover a significant portion of watersheds and affect rainfall interception, water losses through evapotranspiration (ET), surface runoff, and aquifer recharge. Despite their critical role in the hydrologic cycle, tree growth and dynamics are typically ignored or superficially considered in watershed modeling studies. This study aims to improve the plant database of the Soil and Water Assessment Tool (SWAT) model for the two dominant pine species in the Southeastern U.S., loblolly pine (Pinus Taeda L.) and slash pine (Pinus Elliotti). Tree growth-related parameters in SWAT were calibrated at field level for four pine plantations across Alabama, Georgia, and Florida. Improved parameter estimates were transferred from the field plots to two nearby forested watersheds with observed streamflow data. Comparison between improved and default parameterizations showed that the improved SWAT outperformed the default model in simulating leaf area index (LAI), biomass accumulation, and ET at all study sites. At the watershed-scale, models considering the improved representation of forest dynamics showed superior performance and reduced uncertainties in predicting daily streamflow, with NSE values ranging from 0.52 to 0.8. Our findings reveal the importance of accurately representing forest dynamics in hydrological models.