Hydrologic Impact of Climate Change in the Jaguari River in the Cantareira Reservoir System

Abstract

A recent drought in Southeast Brazil affected the Cantareira reservoirs system (CRS), which supplies water to São Paulo megacity, and raised concerns on the impacts that climate change may have on the water budget at the watershed scale. We propose to identify the particular and summed contributions of key climatic variables on the variability of the water budget in Jaguari basin, the main CRS tributary, using forcing–response relationships derived from climate projections and individual elasticities of variables to temperature. Besides, we investigated whether hydrological effects of the anomalous drought were comparable to patterns simulated in the future climate. A thoroughly calibrated hydrological model for evapotranspiration (ET) and discharge (Q) was used to address our questions. We found opposite impacts in the future mostly driven by rainfall changes: under increasing (decreasing) rainfall, the mean ET increased (decreased) up to +25% (−10%) and Q increased (decreased) by +90% (−50%). Higher carbon dioxide concentrations strongly depleted the stomatal conductance, and thus the mean ET, which in turn increased the mean Q in near proportions. Major critical impacts for water management are suggested by the results. Even with a small reduction of precipitation, the discharge patterns in the drought event were replicated at similar intensities.