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Literature has suggested that droughts and societies are mutually shaped and, therefore, both require a better understanding of their coevolution on risk reduction and water adaptation. Although the São Paulo Metropolitan Region drew attention because of the 2013–2015 drought, this was not the first event. This paper revisits this event and the 1985–1986 drought to compare the evolution of drought risk management aspects. Documents and hydrological records are analyzed to evaluate the hazard intensity, preparedness, exposure, vulnerability, responses, and mitigation aspects of both events. Although the hazard intensity and exposure of the latter event were larger than the former one, the policy implementation delay and the dependency of service areas in a single reservoir exposed the region to higher vulnerability. In addition to the structural and non-structural tools implemented just after the events, this work raises the possibility of rainwater reuse for reducing the stress in reservoirs. [ABSTRACT FROM AUTHOR]

Climate variability and increasing water demands prioritize the need to implement planning strategies for urban water security in the long and medium term. However, actions to manage the drought risk impacts entail great complexity, such as the calculation of economic losses derived from the combination of severity, duration and frequency under uncertainties in the climate projections. Thus, new approaches of risk aversion are needed, as an integrated framework for resilience gap assessment, for water utilities to cope with droughts, thereby linking drivers of climate, hydrology and human demands. This paper aims to present the economic impacts of risk aversion for water utilities through a framework linking severity, duration and frequency (SDF) of droughts under climate change scenarios. This new model framework addresses the opportunity cost that represent the preparedness for risk aversion to cope with potential future impacts of droughts, involving a set of options for planning of water resources, under different demands and climate projections. The methodology integrates the hydrological simulation procedures, under radiative climate forcing scenarios RCP 4.5 and 8.5, from a regional climate model Eta-INPE, with time horizons of 2007-2040, 2041-2070, and 2071-2099, linked to Water Evaluation and Planning system (WEAP) hydrologic model and under stationary and non-stationary water supply demand assumptions. The model framework is applied to the Cantareira Water Supply System for Sao Paulo Metropolitan Region, Brazil, with severe vulnerability to droughts. By using hydrological simulations with WEAP, driven by Eta-INPE Regional Climatic Model base line scenarios (1962-2005), were characterized the SDF curves. On the one hand, water tariff price associated to calibrated and modelled scenarios constitute supply/demand proxies of the water warranty time delimited by drought duration. Then, profit loss analysis scenarios are assessed for the regional water utility. On the other hand, for drought resilience gap, results show water utility profit losses per period between 1.3 % and 10.3 % of the regional GDP in 2016. Although future economic impacts vary in a same order, non-stationary demand trends impose larger differences in the drought resilience gap, when the future securitization are linked to regional climate outputs. [ABSTRACT FROM AUTHOR]

Freshwater fluxes are influenced by the volume and quality of water at the headwaters of strategic river basins under change. Although hydrologic models provide hypothesis testing of complex dynamics occurring at river basin scales, freshwater quality modelling is still incipient at many river catchments. In Brazil, approximately only one in twenty modelling studies assesses freshwater nutrients, which limits the policies regarding hydrologic ecosystem services. This paper aims to compare freshwater quality scenarios under different land-use/land-cover (LULC) change, one of them related to the Ecosystem-based Adaptation (EbA) approach in subtropical headwaters. Using the spatially semi-distributed SWAT (Soil and Water Assessment Tool) model, nitrate and total phosphorous loads and sediments yield were modelled in Brazilian subtropical catchments ranging from 7.2 to 1037 km2. Part of these catchments are eligible areas of the Brazilian PES-programmes called Water Producer/PCJ and Water Conservator in the Cantareira Water Supply System, which until the drought in 2013-15 had supplied water to 9 million people in the Sao Paulo Metropolitan Region. We considered freshwater quality modelling of three LULC scenarios, with no climate change, as: (i) recent past scenario (S1), with the historic LULC records in 1990, (ii) current land use scenario (S2), considered the LULC for the period 2010-2015 as the baseline, and (iii) future land use scenario (S2+EbA). The latter scenario proposed forest cover conversion with restoration through EbA in protected areas according to the Basin Plan of the Piracicaba-Capivari-Jundiaí (PCJ) watersheds by 2035. The three LULC scenarios were tested with the same records of rainfall and evapotranspiration observations in 2006-2014, which comprised the occurrence of extreme drought events. We propose a new index to assess hydrologic services related to the grey water footprint (greyWF) and water yield estimated. The Hydrologic Services Index (HSI), as a non-dimensional factor to compare water pollution levels (WPL) for referenced and unreferenced catchments, comprise water pollution levels for nitrate, total phosphorus and sediments. On the one hand, leaching simulations of nitrate and total phosphorous allowed for the kregionalization of greyWF at different spatial scales under LULC changes. According to the critical threshold of reference catchments, HSI identified basins in less sustainable and more sustainable areas. On the other hand, conservation practices simulated through the S2+EbA scenario envisaged not only additional and viable best management practices, but also preventive decision making at the headwaters of water supply systems. [ABSTRACT FROM AUTHOR]