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An emergent strategy to target sustainability involves an understanding of the water-energy interconnections. It takes water to produce energy, and it takes energy to source, treat, and distribute water. Sanitation and energy distribution are the world's pre-eminent development challenges. They are a magnifier of poverty, ill-health and mortality, and gender inequality. The word 'nexus' means the understanding of these interdependencies, tensions, and trade-offs. This paper investigates water-energy interconnections through critical analysis. We applied a bottom-up approach to describe Sao Paulo state's river basins, in Southeast Brazil, from the household to the regional scale. Initially, water availability, energy consumption and wastewater treatment data are inferred using per capita data. The subsequent data analysis then considered the positive and negative linkages among the basins. Local and state levels of dependency are also assessed, considering environmental and socioeconomic impacts. The significance of this paper lies in understanding these interconnections and their interdependence within the local context and individuals' behaviour. The results allow a comprehensive analysis of the water-energy Nexus across Sao Paulo state. The critical analysis also shows how the primary drivers contribute to urbanisation levels, population growth, and industrial activities. • Regional WE Nexus analysis is undertaken for the most industrialised state of Brazil. • The increase in wastewater treatment highlights the sustainability path. • Wastewater treatment growth rates are higher than population and GDP rates. • It develops a unique database for future studies using the Nexus approach. • Population growth, GDP, and industrial intensity are the main drivers in the WE Nexus. [ABSTRACT FROM AUTHOR]

Despite its rich water resources, Brazil is increasingly facing extreme hydrologic events such as droughts and floods. The Sao Paulo Cantareira water supply system (CWSS) offers an opportunity to examine the potential economic benefits of nature-based solutions (NbS) to improve water security and reduce the economic cost of drought. This study explores the potential benefits under a counterfactual NbS land-use scenario compared to actual land use and assesses the economic viability of NbS investments in the CWSS. Specifically, we estimate the economic cost of the 2014–2015 drought in Sao Paulo state for the industrial and water sectors served by the CWSS. We estimate the potential avoided costs under the NbS scenario and conduct a cost–benefit analysis of the NbS scenario investments, including both water supply and carbon sequestration benefits. We estimate that the economic losses of this single drought event totaled BRL 1.6 billion. If NbS had been implemented, this cost could have been reduced by 28%. A cost–benefit analysis that includes only the water supply or both the water supply and carbon sequestration benefits indicates that the NbS scenario has a positive net present value of BRL 144 million and BRL 632 million, respectively. Thus, our results highlight the economic viability of the hypothetical NbS investment in mitigating extreme climatic events. [ABSTRACT FROM AUTHOR]

This study describes a collaborative modeling process deployed at the Cantareira Water Supply System (CWSS) in São Paulo City Metropolitan Area, Brazil. The CWSS faces challenges for meeting the increasing water demand, while land-use and climate change and their combined effect on its water cycle and balance have created a complex water resources management problem. Through a stakeholder engagement process—involving scientists and policymakers, the water utility company, and state administration—environmental simulation models were developed to elicit and represent multiple environmental, economic, and policy perspectives, developing a mutual language to communicate and establish common goals of water resources management. Study outputs include estimation of biophysical and economic benefits associated with prioritized native vegetation restoration activities in the source watersheds. These outputs are deployed in support of landscape planning and the decision process integrating multiple stakeholder perspectives in São Paulo state administration, the water utility company, and municipalities. [ABSTRACT FROM AUTHOR]