Abstract
Hydroclimatic extremes, such as very intense precipitation and drought, are expected to increase with global warming, with their cumulative effects potentially posing severe threats for human and natural systems. We introduce a new metric of potential cumulative stress due to hydroclimatic extremes, the Cumulative Hydroclimatic Stress index (CHS), expressed in “equivalent reference stress years (ERSY)” (i.e., the mean annual stress during a present day reference period). The CHS is calculated for wet and dry extremes in an ensemble of 21st century Global Climate Model projections under the RCP8.5 and RCP2.6 greenhouse gas scenarios. Under the high-end RCP8.5 scenario, by 2100, increases in wet and dry extremes add ~155 ERSY averaged over global land areas (~125 for wet and ~30 for dry extremes), with wet hotspots (>250 added ERSY) throughout regions of Asia, Eastern Africa and the Americas, and dry hotspots (>100 added ERSY) throughout Central and South America, Europe, West Africa, and coastal Australia. Inclusion of population exposure in the stress index definition generates a maximum total (dry + wet) potential stress level exceeding 400 added ERSY over Africa, North America, and Australia, which are thus projected to be extremely vulnerable to increases in hydroclimatic extremes. Under the RCP2.6 scenario, which is close to the 2 °C global warming stabilization target set in the Paris agreement, the total hydroclimatic stress is considerably reduced.
Highlights
The cumulative stress is an integrator over time and, since it accounts for the temporal trajectory of changes in extremes, it can be an optimal measure of related risks
We introduce a new metric of the cumulative potential stress due to hydroclimatic extremes, the Cumulative Hydroclimatic Stress index (CHS), which is described in the Methods section
If for a certain period in the future the cumulative number of Equivalent Reference Stress Year (ERSY) is larger than the value that would be obtained by cumulating the ERSY found for the reference period, the excess number of ERSY is a measure of the additional potential stress induced by climate change
Summary
Hydroclimatic extremes can have severe impacts on different socio-economic sectors, such as agriculture, water resources, health, ecosystem services, urban infrastructure, etc.[1,2] This issue is especially important within the global change context because different generations of twenty-first century global and regional climate model projections have consistently indicated a predominant increase of precipitation intensity and wet extremes, along with a decrease in the frequency of precipitation events, and a lengthening of dry periods.[3,4,5,6,7,8,9,10,11]While the occurrence of individual extremes can have devastating impacts at a given time, the cumulative effect of events over time may be a dominant factor in determining the overall stress for a natural or socio-economic system, thereby challenging its resilience.[1,2] For example, there might be thresholds of cumulative stress leading to the collapse of the system or to impacts that are beyond sustainable adaptation options.
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