Simulation Model for Predicting the Effects of Changes in Land Use on Watershed Hydrology

Objective: Land use changes, driven by increase in population, and expansion of commercial interest, are happening in all parts of the world. Reductions in forest area were reported to have resulted in hydrologic changes and consequential disasters. Paired catchment studies were conducted in many parts of the world to assess the effects of changes in forest area on watershed hydrology, but the results from those studies were grounded to the locations of the study and could not be generalized and transferred to other locations. Such studies took very long time, and huge cost, despite many uncontrolled parameters between the catchments. Methods: Conceptual models have been recommended to develop scenarios for changes in land use. A newly developed Watershed Processes Simulation (WAPROS) model has been used for simulating scenarios for land use changes. The study design included: partial conversion of 0, 20, 40 and 60% of agriculture area to impervious area; 0, 20, 40 and 60% of forest area to agriculture; 0, 20, 40 and 60% of forest area to fallow; and complete conversion to forest, and to agriculture area. The reduction and expansion of forest area could be considered as equivalent to deforestation, and afforestation experiments. Findings: The capability of WAPROS model to generate all elemental processes was useful to interpret and link the causes and effects of changes. The scenario results showed: +60% change from forest to impervious area caused -100%, -28.5% and +4.6% changes in overland flow, baseflow and channel flow; +60% change from forest to agriculture caused +6%, -3.9%, and +7.8% changes in infiltration, peak flow and minimum flow. Comparison of 100% conversion to forest, and to agriculture showed higher channel flow and peak flow for full forest, and higher infiltration and evapotranspiration for full agriculture area. Applications/Improvements: The results supported studies that rejected the sponge theory attributed to forests.