The role of climate services for health: Theoretical case studies on heat-health warning systems in India

Extreme heat is a public health concern in South Asia, particularly affecting urban populations due to high density, infrastructure gaps, and socioeconomic vulnerabilities. We assess the health benefits of Heat–Health Warning Systems (HHWS) as a Climate Service for Health (CSH) in urban India and explore their role in enhancing public health interventions in the context of rising heat exposure. We focus on two key outcomes, heat-related all-cause mortality and preterm birth, and estimate the potential impact of HHWS over 2025–2035 using a theoretical modelling framework adapted from Mistry et al. Our model considers three scenarios: no intervention, a baseline public health intervention (Heat Action Plans or Atosiban administration), and an enhanced intervention enabled by HHWS. We apply spatially resolved climate projections, population estimates, and literature-derived exposure–response functions to quantify health outcomes across 1,447 urban areas in India. We assess the robustness of our results using sensitivity and envelope analyses. We project 685,398 heat-related all-cause deaths and 353,014 heat-related preterm births between 2025 and 2035. Under enhanced intervention scenarios, HHWS could avert an additional 4,596 deaths and 6,354 preterm births compared to baseline interventions alone, representing reductions of 0.67% and 1.80%, respectively. While modest, these findings demonstrate the potential for CSH to support anticipatory public health action and improve the timing, uptake, and coordination of existing interventions. Results vary widely with envelope analyses indicating a range of 0–64,671 deaths and 0–42,890 preterm births averted. Our findings highlight the promise and the limitations of CSH. Realizing their impact will require sustained investment in context-specific, user-informed climate services, and greater alignment between climate and health systems. More rigorous evaluation is also needed to strengthen the evidence base for CSH and identify the conditions under which they can most effectively reduce climate-sensitive health risks.