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Heatwave-Related Mortality Across Indian Cities Under Future Climate Scenarios

Ingita Dey Munshi, Abbinav Sankar Kailasam, Sudeep Shukla, K. Shuvo Bakar, Anirban Chakraborti

Abstract

Heatwaves are intensifying as a major climate extreme and have emerged as a growing public health threat in rapidly urbanizing regions such as India. In this study, we integrate long-term heat-related mortality records (1970-2023) with bias-corrected CMIP6 climate projections to quantify future heatwave-related mortality across 67 Indian cities under intermediate (SSP2-4.5) and high-emission (SSP5-8.5) scenarios. A time-series forecasting framework was applied using summer mean temperature as the primary climate driver to project mortality trajectories through the end of the 21st century. Results indicate a strong and sustained increase in heat-related mortality under both scenarios, with multi-fold amplification under SSP5-8.5 relative to SSP2-4.5, reflecting the high sensitivity of health outcomes to emission pathways. Spatial analysis reveals increasing regional divergence under high-emission conditions, with urban regions in the Deccan Plateau, western India, and parts of eastern and northeastern India exhibiting disproportionately higher mortality growth. Multidimensional scaling further highlights emerging clustering of state-level mortality behavior under extreme warming, indicating structurally different regional responses to future heat stress. In contrast, the intermediate mitigation pathway produces more moderate and spatially uniform mortality trends. These findings demonstrate that climate mitigation can substantially reduce both the magnitude and inequality of future urban heat-health burdens. By linking updated climate projections with long-term mortality data at national and sub-national scales, this study provides policy-relevant evidence to support heat adaptation planning and climate-resilient urban development in one of the world's most heat-vulnerable regions.

Heatwave-Related Mortality Across Indian Cities Under Future Climate Scenarios

Abstract

Heatwaves are intensifying as a major climate extreme and have emerged as a growing public health threat in rapidly urbanizing regions such as India. In this study, we integrate long-term heat-related mortality records (1970-2023) with bias-corrected CMIP6 climate projections to quantify future heatwave-related mortality across 67 Indian cities under intermediate (SSP2-4.5) and high-emission (SSP5-8.5) scenarios. A time-series forecasting framework was applied using summer mean temperature as the primary climate driver to project mortality trajectories through the end of the 21st century. Results indicate a strong and sustained increase in heat-related mortality under both scenarios, with multi-fold amplification under SSP5-8.5 relative to SSP2-4.5, reflecting the high sensitivity of health outcomes to emission pathways. Spatial analysis reveals increasing regional divergence under high-emission conditions, with urban regions in the Deccan Plateau, western India, and parts of eastern and northeastern India exhibiting disproportionately higher mortality growth. Multidimensional scaling further highlights emerging clustering of state-level mortality behavior under extreme warming, indicating structurally different regional responses to future heat stress. In contrast, the intermediate mitigation pathway produces more moderate and spatially uniform mortality trends. These findings demonstrate that climate mitigation can substantially reduce both the magnitude and inequality of future urban heat-health burdens. By linking updated climate projections with long-term mortality data at national and sub-national scales, this study provides policy-relevant evidence to support heat adaptation planning and climate-resilient urban development in one of the world's most heat-vulnerable regions.
Paper Structure (14 sections, 6 figures)

This paper contains 14 sections, 6 figures.

Table of Contents

  1. Introduction
  2. Data and methodology
  3. Study area and data
  4. Climate Data and Future Scenarios
  5. Heatwave Identification Framework
  6. Mortality Forecasting Framework
  7. Spatial Pattern Analysis Using Multidimensional Scaling (MDS)
  8. Results
  9. National-Scale Heat-Related Mortality Projections
  10. Spatial Distribution of Future Heat-Related Mortality Across Indian States
  11. Regional Divergence and Clustering of Mortality Trajectories
  12. Multidimensional Scaling Analysis of State-Level Mortality Behavior
  13. Discussions
  14. Conclusion

Figures (6)

  • Figure 1: Geographic distribution of the 67 urban locations used in this study across India. Selected locations represent diverse climatic regions, including coastal zones, arid and semi-arid plains, plateau regions, and high-altitude environments, and correspond approximately to the spatial resolution of CMIP6 climate model grids.
  • Figure 2: Methodological workflow of the heatwave–mortality projection framework.
  • Figure 3: Temporal evolution of predicted heat-related mortality from 2024 to 2100 aggregated at the national level. The orange line represents SSP5-8.5 and the yellow line represents SSP2-4.5, showing a steeper mortality increase under the high-emission scenario due to stronger radiative forcing (8.5 W/m$^2$ vs. 4.5 W/m$^2$). The model was trained using historical data from 1970 to 2006 and validated using data from 2007 to 2023.
  • Figure 4: State-level projected heat-related mortality trajectories under SSP2-4.5 and SSP5-8.5.
  • Figure 5: Two-dimensional multidimensional scaling (MDS) representation of state-level mortality trajectories showing spatial similarity patterns.
  • ...and 1 more figures