Comparative study on societal impacts of and responses to compound drought-heatwave events: six cases in Germany and Jing-Jin-Ji Region (China) since the 19th century

Drought is a costly experience shared by different human societies, and many of its far-reaching impacts on various components of socio-ecological systems tend to be exacerbated by increasingly frequent and intensive compound heatwaves. To provide a historical and systematic perspective of climate-society interplays in different socio-environmental contexts, this study selected Germany (DE) and Jing-Jin-Ji Region of China (JJJ) as study areas, which are dominated by marine and monsoon climates, respectively. Based on climate reconstructions and multilingual written documents, comparisons on three pairs of compound drought-heatwave events (CDHWs) in agrarian societies (DE 1834 / JJJ 1832 events), during industrialization (DE 1921 / JJJ 1920 events), and in recent years (DE 2018 / JJJ 1997 events) were conducted, focusing on pathways to food security, water security, and health. Overall, social development, rather than distinct climate systems or cultural backgrounds, was identified as the main contributor to differences between events.

(1) FOOD SECURITY: In different events, pathways to food insecurity can mostly be summarized as the impact chain of precipitation deficits → natural system (insect plague, soil moisture) → production system (crop performance) → consumption system (price) → food security. Heatwaves here aggravated existing drought impacts on natural system and production subsystem. Reactive actions to balance food supply and demand after harvest failures were commonly observed in many cases. However, it was not until entering modern societies that survival-threatening manifestation (i.e., food crisis) and subsequent health and/or social issues (e.g., starvation, displacement, crimes) were averted, thanks to stronger  interventions at earlier links in the impact chain (e.g., retain soil moisture, compensate for harvest losses by techniques or imports).

(2) WATER SECURITY: Under different circumstance, a common impact chain leading to water insecurity was also recognized, namely precipitation deficits → natural system (surface water and groundwater) → infrastructure subsystem (water facilities) → water security. Heatwaves here not only exacerbated hydrological deficits in natural system but also stressed infrastructure subsystem by increasing water consumption. Water transport, storage and restriction were temporary measures commonly taken at different development stages, while long-term actions towards sustainable water management and resilient water supply were peculiar to modern societies. Nevertheless, survival-threatening manifestation (i.e., insufficient drinking water) was still reported in recent years, as abovementioned efforts were either difficult to maintain in prolonged CDHWs or took time to be effective. This suggested a greater need for anticipatory adaptation.

(3) HEALTH: Heatwaves has replaced drought as the dominant climatic impact-driver of mortality in recent CDHWs, with a short impact chain of extreme heat → health. Different from the creeping nature of drought, heat manifests as a direct shock to individuals, which means that the time-honored coping strategy of gradually restoring supply-demand balance for scarce resources is less applicable in this case. Currently, prevailing interventions in heat threats to health in both study areas are developing warnings systems for extreme weathers, giving advice on heat protection, adjusting working hours, and changing consumption habits. However, none of them is sufficient to avoid heat-induced mortality, which implied a common adaptation gap on the warming planet.