Executive Summary
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Hydrology Analysis The Water Evaluation and Planning Model (WEAP) was used to estimate hydrological responses to climate change. However, before the outputs from the climate analysis could be used as inputs for the hydrology analysis, WEAP had to be adapted to handle the region’s specific conditions. Glacier and páramo modules were developed to complement an existing and flexible water resources management tool to integrate climate impacts in the hydrological response in mountainous regions. The glacier module allows the model to reflect the dynamic behavior of glaciers and estimate their net contribution to runoff. The páramo module does the same with high mountain wetlands. WEAP was selected for its flexibility to integrate the addition of glacier and páramo modules.2 Although the purpose of this study is to develop a useful methodology, and not necessarily to produce an assessment of the impacts of climate change at a basin level, this report nonetheless also discusses how hydrology might be impacted by the projected consequences of climate change. The analysis includes an estimate of increases in temperature, changes in precipitation, and rate of glacier retreat.
Results of the Case Study Analysis The model was first calibrated in sub-basins that do not have glacier coverage to check the existing rainfall-runoff routines. Based on the initial findings of the calibration in nonglaciated river basins, the model was applied to the Santa and Mantaro-Rímac Basins. The modeling period for calibration was 1970–1984, and the 1985–1998 period was used for validation. In the Santa Basin, the analysis projects lower mean runoffs by mid-century, including decreased year-round monthly runoffs at the La Balsa station, the diversion point for Cañón del Pato, an important power generation facility. The mean reduction is projected to be 21 percent by 2050–2059 compared with the present. Similarly, average flows at the Condocerro station, in the lower part of the Santa River Basin, are projected to decrease by six percent. The minimum flows at this station are projected to decrease by 18 percent. The Mantaro-Rímac Basins are more complex to simulate given the high level of man-made infrastructure for water storage and runoff regulation, including dams and channels. Nevertheless, some interesting results were obtained. The expected response to future climate conditions in the Mantaro Basin indicates a shift in the distribution of runoffs as well as a reduction in peak flows. Overall, discharges at key points in the basin seem to decrease. Conversely, at Rímac, projected conditions indicate no significant changes and at the most suggest the possibility for a slight reduction during the dry season. The results of the simulation of the glacier evolution in the Santa and MantaroRímac River systems were also consistent with historical records.
Conclusion On the basis of the results obtained, it seems that the combination of the climate and hydrology analysis can simulate current conditions at a regional and basin level and project future hydrological conditions. The methods employed could be of use to predict future impacts of climate change on hydrology for other mountain basins in the Andes.