Although deaths and economic losses due to extreme heat are rising globally, heatwaves remain a "hidden hazard" whose impacts are underrecognized due to measurement and valuation challenges. Cities in India are developing Heat Action Plans that combine physical cooling measures (such as urban greening and reflective roofs) with public health measures (such as heat-health early warning systems). However, there is a key knowledge gap on the relative efficacy of these actions. To inform debate on how scarce public funds could most efficiently be allocated to reduce deaths and productivity loss due to extreme heat, this paper develops spatially explicit heat risk maps for Lucknow, Chennai, and Surat under climate scenarios
models future health and economic losses under a "no intervention" scenario
and estimates the costs and benefits of alternative sets of heat mitigation actions. The modeling suggests that by 2050, the number of heat-related deaths could rise by one-third for the case study cities, while labor productivity losses could affect between 2 and 4 percent of their economic output. Among the interventions typically considered in city Heat Action Plans, benefit-to-cost ratios are favorable but vary significantly. Urban greening investments more than cover their costs based on the health and labor productivity benefits of the heat stress reduction they yield (benefit-cost ratio of 3:1). However, heat-health early warning systems offer the greatest harm reduction per dollar invested (benefit-cost ratios exceeding 50:1), suggesting that they are "low-hanging fruit" whose wider implementation across Indian and global cities should be prioritized.