heat wave of May 2010 (Azhar et al 2014). The action plan – which combines short-run actions to prevent deaths during an active heatwave with long-run investments in cooling city spaces through vegetation and building design – was credited with averting some 1,200 deaths per year in the city in the years immediately after its introduction (Hess et al, 2018). Its model of a ‘threshold-based’ heat action plan, in which localized temperature thresholds based on all-cause mortality data are used to trigger sector-specific actions in the health system, labor practices and public communications (among other domains), was recognized by the National Disaster Management Agency (NDMA) as a model for the development of city-wide heat action plans across the country.

A key feature of city Heat Action Plans as implemented in India and internationally is the large number of stakeholders that need to be involved for their successful implementation. Given the diverse physical and social settings in which heat stress affects humans – including homes, workplaces, streetscapes, transport settings, and public amenities such as hospitals and schools – agencies responsible for city planning, transportation and buildings management may have capacity to reduce heat within their sphere of influence. During a heat emergency, stakeholders that have points of contact with vulnerable individuals include city health departments, health care providers, employers, labor unions, community associations, NGOs and media (Knowlton et al. 2014). Adding complexity to the development of Heat Action Plans is the range of policy instruments that vary from direct governmental interventions (e.g., publicly funded heat wave alert system, provision of emergency medical care, green spaces) to mandatory regulations (e.g., building code amendments) as well as incentive-based and information-based interventions (e.g., subsidies for cool roofs and public awareness campaigns on staying healthy during extreme heat).

Studies have established heat mitigation benefits of (i) ‘place-based’ interventions such as urban greening and cool building materials, (ii) ‘people-based’ interventions such as heat health early warning systems as well as (iii) ‘resource-based’ interventions such as additional water and electrical power during heat waves (Roberts et al, ibid). A review of 220 studies of vegetation, water or cool building material-based interventions found that temperatures at project sites fell by up to 2°C in approximately two-thirds of cases and by more than 2°C in the remaining cases (Santamouris et al, 2017). Introduction of heat health warning systems in Asian, North American and European settings have shown reduction in excess mortality of 30% or more vis-à-vis expected levels (see studies of Hong Kong SAR, China; Ahmedabad; Florence; and Milwaukee, respectively: Chau, Chan and Woo 2009, Hess et al, 2018, Morabito et al. 2012, Weisskopf et al, 2002). However, while existing studies have created a rich evidence base on the efficacy of individual heat mitigation actions, less research has been conducted on their relative costs and benefits. This is an important gap since city leaders face resource constraints and a consequent need to prioritize among heat mitigation options.

This paper contributes to the literature in two ways. First, we estimate impacts of extreme heat for Indian cities in a no-intervention scenario. Second, we identify feasible packages of heat mitigation interventions that could feasibly be adopted by Indian cities. We introduce two intervention packages, namely 'medium ambition' and 'high ambition,' which vary in terms of resource requirements (see Table 1). We then assess the potential costs and benefits of these 3