Time of Emergence of Record-shattering Compound Extreme Precipitations Preconditioned by Heatwaves and Their Socio-economic Exposures

Heatwaves and extreme precipitations are the two prevalent types of weather-related extreme events globally. Compared with univariate extremes, impacts of compound extreme precipitations preconditioned by heatwaves (CHEPs) on the society and economy can be amplified. Previous studies demonstrated that heatwaves can trigger extreme precipitations by enhancing atmospheric instability and moisture-holding capacity. Other studies projected future changes in CHEPs under various greenhouse gas emission scenarios. However, there is a lack of studies assessing the time of emergence (ToE) of CHEP change signals, especially for record-shattering events. Since current water resource management strategies and infrastructures are based on historical data, it is crucial to understand when hydro-meteorological conditions will surpass unprecedented levels to develop effective adaptation and mitigation strategies for climate change.

Here, we present a global analysis of ToE for record-shattering CHEPs as well as their exposed GDP and population (POP). Both the frequency and magnitude of observed CHEPs have substantially increased during the past 65 years at the global scale. Using climate models from Detection and Attribution Model Intercomparison Project, we find that rarer CHEPs are increasingly attributable to anthropogenic greenhouse gas emissions, while aerosol emissions have a mitigating effect on their occurrences. To detect when historical record-shattering events will become normal, we develop a novel framework based on advanced Single Model Initial-condition Large Ensemble simulations. Our results indicate that CHEP hotspots, including East and Southeast Asia, North-central South America, and Central Africa, are likely to experience earlier ToE compared to other regions. In contrast, arid regions, such as North Africa, West Asia, and southwestern Australia, show no signs of ToE until at least 2100. GDP and POP exposure to such events reveal an alarming upward trend throughout the 21st century. By the late 21st century, 41% (29%) of sub-regions defined by the Sixth Assessment Report of the Intergovernmental Panel on Climate Change are projected to experience GDP exposure exceeding 4,000 billion USD (at 2010 purchasing power parity) to record-shattering frequency (magnitude), while 34% (27%) are expected to have POP exposure exceeding 100 million under the SSP2-4.5 scenario. Record-shattering CHEPs pose a distinct threat to the economy between 21.75°N and 53.25°N, with the most significant impact between 35.25°N and 39.75°N. Compared to the GDP exposure, the POP exposure hotspots shift toward lower latitudes, with a broader range extending from 0.75°S to 53.25°N. Additionally, we classify areas based on the Human Development Index and income levels defined by the World Bank. The unequal distribution of GDP and POP exposure reveals the poorest and least developed countries will experience more extended impacts compared to wealthier nations. This study highlights the urgent need for region-specific mitigation and adaptation strategies to combat climate change, especially for the vast high-risk and low-income regions.