Assessing urban water insecurity under access inequality - coupled human-natural systems analyses in the Upper Bhima Basin, India

Adapting to growing urban water scarcity requires accurate assessments of present and future water security challenges. An estimated 1 billion people live in cities with intermittent public water supply, often resulting in highly unequal access to water. Under these conditions, households with below-average water access are most exposed to water insecurity. As a result, the full extent of water insecurity could substantially exceed the impacts identified by aggregate water security metrics. Here, we extend an existing coupled human and natural system model of the entire water sector in the Indian Upper Bhima basin, in order to analyze the degree to which water access inequality exacerbates urban water insecurity. The model integrates hydrologic modeling with urban water allocation institutions and water user agents, using data from a quantitative survey of almost 2,000 households in and around Pune, remote sensing data, as well as village-level census and water supply data. We use the model to assess water security impacts under historical and future droughts and various levels of supply augmentation. We find that a large share of households falls below critical water security thresholds before impacts are detected by aggregate metrics. While an unequal water distribution prevails, supply augmentation projects require several times the scale to meet given per capita water supply targets across the population than they would under a more equitable distribution. The findings demonstrate the extent to which current assessments of future urban water insecurity can underestimate the challenges ahead.