Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming1, 2, 3. Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming4, 5. The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change6. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation7 that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles8 that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years. The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years9, 10.
At a glance
- Projected changes in drought occurrence under future global warming from multi-model, multi-scenario, IPCC AR4 simulations. Clim. Dyn. 13, 79–105 (2008) &
- Drought under global warming: a review. Wiley Interdisc. Rev. Clim. Change 2, 45–65 (2010)
- 109–230 (Intergovernmental Panel on Climate Change, 2012) et al. in Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (eds et al.)
- A global data set of Palmer Drought Severity Index for 1870–2002: relationship with soil moisture and effects of surface warming. J. Hydrometeorol. 5, 1117–1130 (2004) , &
- van der Schrier, G. & Jones, P. D. Wet and dry summers in Europe since 1750: evidence of increasing drought. Int. J. Climatol. 29, 1894–1905 (2009)
- Pan evaporation trends and the terrestrial water balance II. Energy balance and interpretation. Geog. Compass 3, 761–780 (2009) , &
- An approach toward a rational classification of climate. Geogr. Rev. 38, 55–94 (1948)
- Natural evaporation from open water, bare soil, and grass. Proc. R. Soc. Lond. A 193, 120–145 (1948)
- Drought variations in the eastern part of northwest China over the past two centuries: evidence from tree rings. Clim. Res. 38, 129–135 (2009) et al.
- Seasonal shift in the climate responses of Pinus sibirica, Pinus sylvestris, and Larix sibirica trees from semi-arid, north-central Mongolia. Can. J. For. Res. 41, 1242–1255 (2011) et al.
- Regional drought has a global impact. Nature 472, 169 (2011)
- Rising temperature depletes soil moisture and exacerbates severe drought conditions across southeast Australia. Geophys. Res. Lett. 36, L21709 (2009) , , &
- IPCC. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (eds 2007) et al.) (Cambridge Univ. Press,
- Characteristics of the dry/wet trend over arid central Asia over the past 100 years. Clim. Res. 41, 51–59 (2010) , , &
- 1965) Meteorological Drought (US Department of Commerce Research Paper 45,
- Drought-induced reduction in global terrestrial net primary production from 2000 through 2009. Science 329, 940–943 (2010) &
- The Palmer Drought Severity Index: limitations and assumptions. J. Clim. Appl. Meteorol. 23, 1100–1109 (1984)
- A self-calibrating Palmer drought severity index. J. Clim. 17, 2335–2351 (2004) , &
- 4.1–4.53 (McGraw-Hill, 1993) in Handbook of Hydrology (ed. )
- On the attribution of changing pan evaporation. Geophys. Res. Lett. 34, L17403 (2007) , , &
- Assessing the ability of potential evaporation formulations to capture the dynamics in evaporative demand within a changing climate. J. Hydrol. (Amst.) 386, 186–197 (2010) , &
- Assessing temperature-based PET equations under a changing climate in temperate, deciduous forests. Hydrol. Process. 25, 1466–1478 (2011) &
- Evaporation and environment. Symp. Soc. Exp. Biol. 19, 205–234 (1964)
- Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900–2008. J. Geophys. Res. 116, D12115 (2011)
- The sensitivity of the PDSI to the Thornthwaite and Penman–Monteith parameterizations for potential evapotranspiration. J. Geophys. Res. 116, D03106 (2011) , &
- On the ‘Divergence Problem’ in northern forests: a review of the tree-ring evidence and possible causes. Global Planet. Change 60, 289–305 (2008) , , &
- Changes in Australian pan evaporation from 1970 to 2002. Int. J. Climatol. 24, 1077–1090 (2004) &
- On the recent warming in the Murray–Darling Basin: land surface interactions misunderstood. Geophys. Res. Lett. 36, L24405 (2009) , &
- Observational evidence for soil-moisture impact on hot extremes in southeastern Europe. Nature Geosci. 4, 17–21 (2011) et al.
- On the hydrologic adjustment of climate-model projections: the potential pitfall of potential evapotranspiration. Earth Interact. 15, 1–14 (2011) &
- Development of a 50-yr high-resolution global dataset of meteorological forcings for land surface modeling. J. Clim. 19, 3088–3111 (2006) , &
- The Drought Monitor. Bull. Am. Meteorol. Soc. 83, 1181–1190 (2002) et al.
- Drought reconstructions for the continental United States. J. Clim. 12, 1145–1162 (1999) , , &
- Summer moisture availability across North America. J. Geophys. Res. 111, D11102 (2006) , , &
- Multidecadal climate variability of global lands and oceans. Int. J. Climatol. 26, 849–865 (2006) &
- Characteristics of global and regional drought, 1950–2000: analysis of soil moisture data from off-line simulation of the terrestrial hydrologic cycle. J. Geophys. Res. 112, D17115 (2007) &
- 1973) Consumptive Use of Water and Irrigation Water Requirements (American Society of Civil Engineers,
- Development of a global evapotranspiration algorithm based on MODIS and global meteorology data. J. Geophys. Res. 112, G01012 (2007) et al.
- Regional evaporation estimates from flux tower and MODIS satellite data. Remote Sens. Environ. 106, 285–304 (2007) , , &
- Long-term regional estimates of evapotranspiration for Mexico based on downscaled ISCCP data. J. Hydrometeorol. 11, 253–275 (2010) , &
- The NCEP/NCAR 40-Year Reanalysis Project. Bull. Am. Meteorol. Soc. 77, 437–471 (1996) et al.
- An improved method of constructing a database of monthly climate observations and associated high-resolution grids. Int. J. Climatol. 25, 693–712 (2005) &
- The TRMM Multisatellite Precipitation Analysis (TMPA): Quasi-global, multiyear, combined-sensor precipitation estimates at fine scales. J. Hydrometeorol. 8, 38–55 (2007) et al.
- Surface Radiation Budget Project completes 22-year data set. GEWEX News 16, 12–13 (2006) , , , &
- Global land precipitation: a 50-yr monthly analysis based on gauge observations. J. Hydrometeorol. 3, 249–266 (2002) , , &
- Global precipitation analysis products of the GPCC. Weather and Climate—Deutscher Wetterdienst—Klimadatenzentrum-WZN <ftp://ftp-anon.dwd.de/pub/data/gpcc/PDF/GPCC_intro_products_2008.pdf> (2008) , , &
- Terrestrial Air Temperature: 1900–2008 Gridded Monthly Time Series, version 2.01. Global Air Temperature Archive <http://climate.geog.udel.edu/~climate/html_pages/Global2_Ts_2009/README.global_t_ts_2009.html> (2010) &
- Supplementary Information (3.3M)
This file contains Supplementary Text, Supplementary Figures 1-19, Supplementary Table 1 and Supplementary References.