Multimodel assessment of water scarcity under climate change

TLDR

Water scarcity threatens food security and economic prosperity, and future population growth and climate‑driven changes in precipitation and temperature are expected to further increase pressure on water resources. The study synthesizes knowledge on climate‑change impacts on water resources by using a large ensemble of global hydrological models driven by five global climate models and Representative Concentration Pathway scenarios. We employed a large ensemble of global hydrological models forced by five global climate models and Representative Concentration Pathway scenarios to assess water scarcity under climate change. The ensemble projects that a 2 °C warming will increase severe water scarcity for an additional ~15 % of the global population and raise absolute scarcity by ~40 % (up to >100 % in some models), with moderate impacts peaking between present and 2 °C and very severe impacts rising beyond 2 °C, while large uncertainties—especially from hydrological models—highlight the need for improved projections.

Abstract

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m(3) per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.