Quantifying the water budgets of rainforests is important for local forest management to achieve multiple ecosystem services such as water supply and carbon sequestration. However, the water budgets of tropical rainforests remained largely uncertain due to their unique climate and technical limitations in field measurements. Here we developed a water budget for the El Yunque National Forest (ENF) in Puerto Rico by combining field monitoring, remote sensing products, and improved ecohydrological modeling with the Water Supply Stress Index (WaSSI) model. We identified the uncertainties of the water balance components.
Results/Conclusions
Our study indicated that a new evapotranspiration model derived from eddy flux data for rainforests improved model performance in quantifying runoff (Q) and Runoff /Precipitation (Q/P) ratios. The modeled annual Q and Q/P were 1795 mm yr-1 and 63% for the ENF region, representing the highest in the U.S. National Forests system. We also showed that the modeled evapotranspiration (ET) was significantly (r=0.57, RMSE=27.7 mm month-1, p<0.01) correlated to MODIS ET, but large differences in seasonal and annual values were found. The P, Q, and ET fluxes estimated in the literature varied greatly in terms of both the magnitude and seasonality across the study region because of the disparities in the research methods, scales, and/or data sources. This study shows the necessity of improved monitoring efforts toward the water budgets in tropical rainforests for a sustainable management of the water resources.