Ecohydrological dynamics of tropical watersheds in response to land use and climate changes

Background/Question/Methods

Both land use and climate changes can alter the ecohydrological processes in coastal wetlands and their vicinity, and the Globwetlands project emphasizes the importance of integrated analysis at watershed scales. We propose an integrated modeling effort to address the vulnerability of coastal wetlands to changed land use and climate, by adopting the SWAT (Soil and Water Assessment Tool) watershed model, which will then be coupled with the CLUE-s (Conversion of Land Use and its Effect) land use model. SWAT is an ecohydrological model to simulate the interaction between the biological component and the hydrological cycle within a watershed ecosystem. We parameterize the model for the watersheds of Rio Espiritu Santo, Rio Grande de Loiza near Caguas, Rio Guanajibo at Hormiqueros, Rio Gurabo near Caguas, Rio Fajado, Rio Blanco, Rio Cibuco, and Rio Gulebrinas in Puerto Rico, US. These watersheds represent the landscape-scale ecosystems of great-rainfall in northeast, moderate-rainfall in central mountains, and low-rainfall in southwest. 

Results/Conclusions

The simulated water discharges from the watersheds caught the major storms and droughts events, and agreed well with the monitored USGS water discharge measurement. Water discharge of tropical watersheds is primarily determined by rainfall. Our analysis indicates land use land cover significantly regulated the response of discharge to variation of rainfall. Specifically the discharge is reduced by pasture fraction and the parameter-area ratio of pasture. The effects of forest and other land covers did not appear in the regression analysis largely because the forest is often located in high elevation with reduced evapotranspiration. Both landscape composition and configuration have controls to the watershed discharge for given amount of rainfall.