Seasonal hydrologic response to land use change and climate change in a tropical montane cloud forest in Veracruz, Mexico

Abstract

We studied three adjacent catchments located within the seasonal cloud forest belt in Central Veracruz, Mexico to understand the effects of land use change and climate change on discharge in these catchments. We gained such understanding from virtual experiments with a distributed hydrological model. Hydrological models would benefit from a more spatially distributed input for saturated hydraulic conductivity (Ksat) of the soil. We determined the spatial variability of (Ksat) in a pasture catchment and studied the relation between Ksat and penetration resistance of the soil, which is much easier to measure in the field, to enhance and facilitate a spatially distributed Ksat input in future hydrological modeling studies.

Below 50 cm depth, Ksat curves are found to be similar along the slope in the pasture catchment. Comparing the Ksat curves between pasture and forest we also conclude that below 50 cm depth, hydraulic conductivities are similar for both land use types. Differences in the upper 10 cm of the soil are yet unknown but are expected to be large between pasture and forest. More measurements are needed in the pasture catchment to determine Ksat behavior in the upper 10 cm of the soil. Saturated hydraulic conductivity is negatively correlated with penetration resistance, with R2 values of 0.65 and 0.71. Our findings suggest that penetration resistance measurements can be used to determine Ksat behavior in the field.

Conversion from pasture to a naturally regenerated secondary forest leads to a more fluctuating stream discharge and higher discharges during the wet season. Forest removal for pasture results in a total annual increase of discharge, where the bulk of the increase is observed in the dry season in the form of baseflow rather than an increasing response to rain events in the wet season. Climate change scenarios with rising temperatures cause small decreases in streamflow in the forest catchments, due to higher potential evaporation rates. As a result of more extreme rainevents we find total annual increases in streamflow in all three catchments. For the pasture catchment, this increase is found twice as high as for the two forest catchments, probably due to infiltration excess overland flow in the pasture catchment. Increases in streamflow occur during the wet season, when the mature forest and secondary forest more frequently experience saturation overland flow.