| Summary: | Paramo is very susceptible to land use and climate change, and afforestation of paramo ecosystems with pine is a common practice. The effects of pine plantations are multiple, including on the basin's hydrology. To gather insight into the impact of afforestation on the hydrology of a river basin a comparative study was conducted with the objective to derive answers to the following questions: 1) How to calibrate the parameters of hydrological models subject to land use change? 2) What is the impact on peaks, total flow, and baseflow when land use gradually changes from tussock-grass to pine plantation? and 3) Is the impact different when land use changes gradually from upstream to downstream (U-D) or from downstream to upstream (D-U)? The research was conducted on two paired catchments, respectively the Zhurucay basin with tussock grass vegetation and the Mpinos basin with pine plantation. The hydrology was simulated with the HBV-light software. In addition to the traditional calibration, the baseflow/total flow ratio was used as an objective function. This procedure shows a considerable improvement in the sensitivity of the PERC parameter, improving the calibration of the model to mimic land use change. After calibration and validation, scenarios of land use change were simulated by transferring the calibrated parameter values. The results show that total flow and baseflow are respectively reduced by 21% and 66% and peaks reduce on average 21% but individually they can drop up to 61%. Also, we found that the impact is stronger in dry periods than in humid periods. The difference in the impact between D-U and U-D approaches is not conclusive and should be further studied. This study presents a calibration approach to quantify the effects of land use change before it is done. These tools are low-cost and could be used in many applications on issues such as land use planning, water resources management, and water conservation.
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