New Research

90% of world’s people to face combined extreme heat and drought

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Compound threats will most severely affect poor people and rural areas

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More than 90% of the world’s population is projected to face increased risks from the compound impacts of extreme heat and drought, potentially widening social inequalities as well as undermining the natural world’s ability to reduce CO2 emissions in the atmosphere — according to a study from Oxford University’s School of Geography.

In the wake of record temperatures in 2022, from London to Shanghai, continuing rising temperatures are projected around the world. When assessed together, the linked threats of heat and drought represent a significantly higher risk to society and ecosystems than when either threat is considered independently, according to the paper, published this month in the journal Nature Sustainability.

These joint threats may have severe socio-economic and ecological impacts which could aggravate social inequality, as they are projected to have more severe impacts on poorer people and rural areas.

According to the research, ‘The frequency of extreme compounding hazards is projected to intensify tenfold globally due to the combined effects of warming and decreases in terrestrial water storage, under the highest emission scenario. Over 90% of the world population and GDP is projected to be exposed to increasing compounding risks in the future climate, even under the lowest emission scenario.’

By using simulations from a large model and a new machine-learning generated carbon budget dataset, they quantified the response of ecosystem productivity to heat and water stressors at the global scale. This showed the devastating impact of the compound threat on the natural world and international economies. Limited water availability will hit the ability of carbon sinks  to take in carbon emissions and emit oxygen.

Abstract of
Future socio-ecosystem productivity threatened by compound drought–heatwave events
Nature Sustainability
, January 5, 2023

Compound drought–heatwave (CDHW) events are one of the worst climatic stressors for global sustainable development. However, the physical mechanisms behind CDHWs and their impacts on socio-ecosystem productivity remain poorly understood.

Here, using simulations from a large climate–hydrology model ensemble of 111 members, we demonstrate that the frequency of extreme CDHWs is projected to increase by tenfold globally under the highest emissions scenario, along with a disproportionate negative impact on vegetation and socio-economic productivity by the late twenty-first century. By combining satellite observations, field measurements and reanalysis, we show that terrestrial water storage and temperature are negatively coupled, probably driven by similar atmospheric conditions (for example, water vapour deficit and energy demand).

Limits on water availability are likely to play a more important role in constraining the terrestrial carbon sink than temperature extremes, and over 90% of the global population and gross domestic product could be exposed to increasing CDHW risks in the future, with more severe impacts in poorer and more rural areas. Our results provide crucial insights towards assessing and mitigating adverse effects of compound hazards on ecosystems and human well-being.