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Future freshwater stress for island populations


Global climate models project large changes in the terrestrial water balance for many regions over this century in response to greenhouse gas emission1,2,3,4,5,6,7,8,9, but insufficient resolution precludes such knowledge for approximately 18 million people living on small islands scattered across the world ocean. By accounting for evaporative demand a posteriori at 80 island groups distributed among Earth’s major ocean basins, we reveal a robust yet spatially variable tendency towards increasing aridity at over 73% of island groups (16 million people) by mid-century. Although about half of the island groups are projected to experience increased rainfall—predominantly in the deep tropics—projected changes in evaporation are more uniform, shifting the global distribution of changes in island freshwater balance towards greater aridity. In many cases, the magnitude of projected drying is comparable to the amplitude of the estimated observed interannual variability, with important consequences for extreme events as well as mean climate. Future freshwater stress, including geographic and seasonal variability, has important implications for climate change adaptation scenarios for vulnerable human populations living on islands across the world ocean.

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Figure 1: Future aridity changes.
Figure 2: Internal variability of aridity.
Figure 3: Seasonal changes in aridity.
Figure 4: Effects of precipitation and evaporation.


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K.B.K. and J.P.D. acknowledge support from the Strategic Environmental Research and Development Program (SERDP). SERDP is the environmental science and technology programme of the US Department of Defense (DoD) in partnership with the US Department of Energy (DOE) and the US Environmental Protection Agency (EPA). K.B.K. further acknowledges support from the Alfred P. Sloan Foundation and the James E. and Barbara V. Moltz Fellowship administered by the WHOI Ocean and Climate Change Institute (OCCI). K.J.A. acknowledges support from NSF grant BCS–1263609. The authors thank C. Ummenhofer for helpful discussions. The authors thank NOAA NCDC for providing GHCN station observations. The WHOI—Hawaii Ocean Timeseries Site (WHOTS) mooring is supported by NOAA through the Cooperative Institute for Climate and Ocean Research (CICOR) under Grant No. NA17RJ1223 and NA090AR4320129 to WHOI, and by NSF grants OCE–0327513, OCE–752606, and OCE–0926766 to the University of Hawaii.

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K.B.K. designed the study with substantial contributions from J.P.D. and K.J.A., K.B.K. analysed the data, all authors discussed and interpreted the results, K.B.K. wrote the initial draft of the manuscript, and all authors discussed and interpreted the results and edited the manuscript.

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Correspondence to Kristopher B. Karnauskas.

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Karnauskas, K., Donnelly, J. & Anchukaitis, K. Future freshwater stress for island populations. Nature Clim Change 6, 720–725 (2016).

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