Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km 2 ; water supply) and Emborcação (29,076 km 2 ), Três Marias (51,576 km 2 ), Furnas (52,197 km 2 ), and Mascarenhas (71,649 km 2 ; hydropower) for hydrological modelling. It made the first attempt at configuring a season-based probability-distributed model (PDM-CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra-annual and interannual variability of the upstream inflows during 1985-2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash-Sutcliffe efficiency and logarithmic Nash-Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984-2001, 0.87 and 0.88 for the validation period 2001-2010, and 0.93 and 0.90 for the validation period 2010-2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season-based PDM-CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM-CEMADEN is a simple, efficient, and easy-touse model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large-sized upstream basins. KEYWORDS 2014/2015 water crisis, intra-annual and interannual rainfall variability, PDM-CEMADEN, seasonal calibration, southeastern Brazil
During the 2014-2016 water shortage crisis, the Metropolitan Area of São Paulo (MASP) water supply system extracted pumping volume from the Cantareira System. Before the crisis, between 1984 and 2013, the reservoir's average water extraction flow was 29.6 m 3 •s −1. During the period of pumping volume usage, the average extraction flow was 16.2 m 3 •s −1. Following the crisis, two new mitigation policies were implemented: a water extraction Resolution (in 2017) and a Resolution for water reallocation from another basin (in 2018). This study provides a novel investigation of the Cantareira System water crisis by assessing the mitigation policies impacts on storage level dynamics. The system storage level was evaluated using the reservoir simulation module of PDM-Cemaden hydrological model, assuming that the new policies had already been implemented prior to the crisis. A control simulation was run with observed in-and out-flow and operationally-practiced extraction flow. The storage level dynamics impacts were evaluated under 4 water mitigation policies scenarios varying the policies implementation starting date, the extraction flow range and including the water reallocation variable. Results showed that pumping volume would only need extraction during a short period (Scenarios I, III and IV), and considering the water reallocation, pumping volume extraction would not have been necessary (Scenario II
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