Study with policy implications reveals climate change, and not population growth, plays the main role in predicting extreme droughts
From Stony Brook University
Common belief states that the dominant factor determining water scarcity in the next few decades will be population growth. However, according to a new study by Stony Brook University, it’s climate change — not population growth – that plays the main role in predicting future exposure to extreme droughts.
The study published in Climatic Change: “The relative importance of climate change and population growth for exposure to future extreme droughts,” looks at the future global and national populations’ exposure to extreme drought, based on an ensemble of 16 climate models and UN population growth projections.
Exposure to extreme droughts
The results imply that cutting greenhouse gas emissions should be the primary policy response for decreasing the number of people exposed to future extreme droughts. Population growth, while playing an important role for populations’ drought exposure in some countries, is a less significant force, one for which developing nations should not be held responsible.
Among the highlights:
•By the end of the century (2081-2100), the number of people exposed to extreme drought will increase by 426.6% relative to the present, under the business-as-usual emissions.
•Climate change alone is responsible for 59.5% of the increase.
•Population growth alone is responsible for 9.2% of the increase.
•Climate change and population growth combined effect (technically, “interaction”) is responsible for 31.4%.
•129 countries will experience increase in drought exposure mainly due to climate change alone.
The human consequences of drought are normally addressed in terms of “water scarcity” originating from human water use. In these terms, a common prediction to the next few decades is that population growth, not climate change, will be the dominant factor determining numbers living under such scarcity. Here we address the relative importance of increasing human caused extreme drought and increasing population for numbers of humans likely to be directly exposed in the future to such drought. Using the Standardized Precipitation Evapotranspiration Index (SPEI) in conjunction with an ensemble of 16 CMIP5 climate models we find that, by 2081-2100 under the high emissions scenario RCP 8.5, average worldwide monthly population exposed to extreme drought (SPEI < -2) will increase by 386.8 million to 472.3 million (+426.6% from the current 89.7 million). Anthropogenic climate change is responsible for approximately 230.0 million (59.5%) of that increase with population growth responsible for only 35.5 million (9.2%); the climate change-population growth interaction explains the remaining 121.1 million (31.4%). At the national level, 129 countries will experience increase in drought exposure mainly due to climate change alone; 23 countries primarily due to population growth; and 38 countries primarily due to the interaction between climate change and population growth. Given inherently large uncertainties, projections of future climate impacts should be accepted with caution especially those directed to the regional level, to future population trends, and, of course, where technological, social and security changes are possible.
Oleg Smirnov, Minghua Zhang, Tingyin Xiao, John Orbell, Amy Lobben and Josef Gordon; The relative importance of climate change and population growth for exposure to future extreme droughts; Climatic Change DOI: 10.1007/s10584-016-1716-z
Stony Brook University news release issued via Newswise.