MODELING THE EFFECTS OF HYDROLOGIC SERVICE PAYMENTS ON THE HYDROLOGY OF TROPICAL MONTANE WATERSHEDS IN CENTRAL VERACRUZ, MEXICO.

Abstract

An analysis of the effects of the Land Use Land Cover (LULC) change and its impacts on the hydrological cycle of tropical montane catchments influenced by cloud forest (TMCF) is developed in Central Veracruz, Mexico. This work started with the analysis of data from monitored-micro-catchments with contrasting LULC. Later the suitability of an improved version of the Soil and Water Assessment Tool model for the Tropics (SWAT-T) was evaluated. Finally, potential future land use scenarios, including conservation targeting alternatives were evaluated using a calibrated Seasonal Water Yield model as part of the Integrated Valuation of Ecosystem Services and Tradeoffs framework (InVEST-SWY). High-resolution rainfall and streamflow timeseries suggested no statistical difference in the regulation capacity of high flows in 20 years of natural regeneration, compared to the mature forest. In terms of baseflow sustenance, the mature forest and intermediate age forest better promote this hydrologic service than the other land uses. Shade coffee exhibited a high capacity to modulate peak flows comparable to that of mature forest, and an intermediate capacity to sustain baseflow. Finally, forty years of intense pasture management caused a fivefold greater peak flow response and a lower baseflow compared to mature forest. SWAT-T accurately simulated the observed low fraction of surface runoff. However, it incorrectly predicted the dominance of lateral flow, instead of the deep groundwater flow observed from isotope-based studies. Moreover, SWAT-T underestimated the influence of rainfall interception losses in forests. The temperature-based potential evapotranspiration methods produced the best model fit (KGE = 0.75, NSE = 0.54, PBIAS = 4.6%), but overestimated the PET in land covers with lower rainfall interception. Finally, the model largely overestimates the low flow in managed land covers, while underestimating it in forests. The InVEST-SWY model predicted that forest conservation policy will produce a slight decrease in the annual water yield at catchment scale due to larger evapotranspiration rates observed in forests. However, the model was unable to mimic the effects of forest conservation on dry-season baseflow. InVEST-SWY exhibited a poor performance at interannual scale and needs improvements to incorporate the water storage capacity of the soils.