Water Scarcity Risk Index: A Tool for Strategic Drought Risk Management

Drought events have affected many regions of the world, having negative economic, environmental and social impacts. When accompanied by increasing water demands, these events can lead to water scarcity. Since droughts can significantly vary in each geographic area, several indices have been developed around the world. Hazard indexes are commonly used to predict meteorological, agricultural and hydrological droughts. These indexes intend to predict hazards, but they do not provide information on when and where deficits can have negative consequences. This study presents a new planning and decision-support tool for monitoring water scarcity situations in a given region. This tool, called the Water Scarcity Risk Index (W-ScaRI), is formed by two subindices, which are proposed to describe a hazard and its consequences. Each subindex was constructed using a group of indicators and indices selected from the technical literature or originally proposed in this work. The W-ScaRI was applied to the Rio de Janeiro Metropolitan Region (RJMR), supplied with water by the Guandu/Lajes/Acari system. The RJMR is one of the most densely populated regions in Brazil, located in an area that has no natural water bodies capable of meeting its supply needs. Therefore, the Guandu River, which, in fact, is formed by two discharge transpositions from the Paraiba do Sul River, is the main drinking water supply source for this region. The RJMR suffered the consequences of unexpected, prolonged droughts in the Southeast region in 2003 and 2014-2015, leading the local authorities to implement temporary emergency measures in the management system of Paraiba do Sul and Guandu Basins, avoiding water shortage but showing the urgent need for planning and management support tools to anticipate possible future problems. The results of the study show that the formulation of the W-ScaRI can represent the water scarcity risk in a relatively simple way and, at the same time, with adequate conceptual and methodological consistency.