Assessing the contribution of meltwater to meet environmental flow requirements during drought events in the Andean Santa River basin

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Santa River catchment, Cordillera Blanca, Peruvian Andes. The effects of global change on the hydrological cycle are amplified in the highly-dynamic tropics. In the high Andes (identified as a hotspot of climate change), a warming climate impacts the cryosphere, and, therefore, alters the composition of downstream discharge. Quantifying these compositions, and evaluating the contributions of meltwater components, is vital for sustainable water resources management under changing hydrological regimes. For such analyses, we used the spatially-distributed cryosphere-hydrological model ‘Spatial Processes in Hydrology,’ forced with PISCO and RAIN4PE distributed meteorological data to simulate daily discharge components (rainfall-runoff, snowmelt, glacier melt, baseflow). We then computed a compensation metric to assess how meltwater compensated for the lack of rainfall-runoff during drought events, and further evaluated if the compensating flows were sufficient to maintain environmental flow requirements. During 35 drought events, snowmelt contributions tended to decrease, while glacier melt contributions tended to increase. In total, meltwater contributions generally increased, and were able to compensate for reductions in rainfall-runoff. Meltwater proved critical during 85 % of identified drought events to ensure the total discharge reached an environmentally safe threshold. This research advances the understanding of the compensating effect of meltwater during droughts, which can inform water management in glacier-influenced catchments and shed light on climate change impacts in the tropical Andes. • We calculated spatially compensated discharge zones per contributor during droughts. • Meltwater compensated for the lack of rainfall-runoff during warm and dry periods. • Meltwater was critical to meet environmental flow requirements in the catchment.