Uncertainties in historical changes and future projections of drought. Part I: estimates of historical drought changes
TL;DR: This article examined the uncertainties in estimating recent drought changes and recommended using the Global Precipitation Climatology Centre (GPCC) or GPCP datasets over other existing land precipitation products due to poor data coverage in other datasets since the 1990s.
Abstract: How drought may change in the future are of great concern as global warming continues. In Part I of this study, we examine the uncertainties in estimating recent drought changes. Substantial uncertainties arise in the calculated Palmer Drought Severity Index (PDSI) with Penman-Monteith potential evapotranspiraiton (PDSI_pm) due to different choices of forcing data (especially for precipitation, solar radiation and wind speed) and the calibration period. After detailed analyses, we recommend using the Global Precipitation Climatology Centre (GPCC) or the Global Precipitation Climatology (GPCP) datasets over other existing land precipitation products due to poor data coverage in the other datasets since the 1990s. We also recommend not to include the years after 1980 in the PDSI calibration period to avoid including the anthropogenic climate change as part of the natural variability used for calibration. Consistent with reported declines in pan evaporation, our calculated potential evapotranspiration (PET) shows negative or small trends since 1950 over the United States, China, and other regions, and no global PET trends from 1950 to 1990. Updated precipitation and streamflow data and the self-calibrated PDSI_pm all show consistent drying during 1950–2012 over most Africa, East and South Asia, southern Europe, eastern Australia, and many parts of the Americas. While these regional drying trends resulted primarily from precipitation changes related to multi-decadal oscillations in Pacific sea surface temperatures, rapid surface warming and associated increases in surface vapor pressure deficit since the 1980s have become an increasingly important cause of widespread drying over land.
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TL;DR: In this paper, a review describes recent progress in dryland climate change research, showing that the long-term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions while anthropogenic aerosols exert small effects but alter its attributions.
Abstract: Drylands are home to more than 38% of the world's population and are one of the most sensitive areas to climate change and human activities. This review describes recent progress in dryland climate change research. Recent findings indicate that the long-term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions while anthropogenic aerosols exert small effects but alter its attributions. Atmosphere-land interactions determine the intensity of regional response. The largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. The global pattern and inter-decadal variability of aridity changes are modulated by oceanic oscillations. The different phases of those oceanic oscillations induce significant changes in land-sea and north-south thermal contrasts, which affect the intensity of the westerlies and planetary waves and the blocking frequency, thereby altering global changes in temperature and precipitation. During 1948-2008, the drylands in the Americas became wetter due to enhanced westerlies, whereas the drylands in the Eastern Hemisphere became drier because of the weakened East Asian summer monsoon. Drylands as defined by the AI have expanded over the last sixty years and are projected to expand in the 21st century. The largest expansion of drylands has occurred in semi-arid regions since the early 1960s. Dryland expansion will lead to reduced carbon sequestration and enhanced regional warming. The increasing aridity, enhanced warming and rapidly growing population will exacerbate the risk of land degradation and desertification in the near future in developing countries.
439 citations
TL;DR: This study shows drylands have warmed, and will continue to warm, more than the humid lands that are primarily responsible for emissions, and this target is acceptable only for humid lands, whereas drylands will bear greater warming risks.
Abstract: Limiting average global warming to 2 °C will not limit regional warming to the same levels. This study shows drylands have warmed, and will continue to warm, more than the humid lands that are primarily responsible for emissions. The Paris Agreement aims to limit global mean surface warming to less than 2 °C relative to pre-industrial levels1,2,3. However, we show this target is acceptable only for humid lands, whereas drylands will bear greater warming risks. Over the past century, surface warming over global drylands (1.2–1.3 °C) has been 20–40% higher than that over humid lands (0.8–1.0 °C), while anthropogenic CO2 emissions generated from drylands (∼230 Gt) have been only ∼30% of those generated from humid lands (∼750 Gt). For the twenty-first century, warming of 3.2–4.0 °C (2.4–2.6 °C) over drylands (humid lands) could occur when global warming reaches 2.0 °C, indicating ∼44% more warming over drylands than humid lands. Decreased maize yields and runoff, increased long-lasting drought and more favourable conditions for malaria transmission are greatest over drylands if global warming were to rise from 1.5 °C to 2.0 °C. Our analyses indicate that ∼38% of the world’s population living in drylands would suffer the effects of climate change due to emissions primarily from humid lands. If the 1.5 °C warming limit were attained, the mean warming over drylands could be within 3.0 °C; therefore it is necessary to keep global warming within 1.5 °C to prevent disastrous effects over drylands.
403 citations
23 Apr 2018
TL;DR: In this paper, a formulation of drought indices without considering the factors that govern the background state may lead to drought artifacts under a warming climate, and a formulation based on the energy budget framework can be a better approach compared to only temperature-based equations.
Abstract: Droughts occur naturally, but climate change has generally accelerated the hydrological processes to make them set in quicker and become more intense, with many consequences, not the least of which is increased wildfire risk. There are different types of drought being studied, such as meteorological, agricultural, hydrological, and socioeconomic droughts; however, a lack of unanimous definition complicates drought study. Drought indices are used as proxies to track and quantify droughts; therefore, accurate formulation of robust drought indices is important to investigate drought characteristics under the warming climate. Because different drought indices show different degrees of sensitivity to the same level of continental warming, robustness of drought indices against change in temperature and other variables should be prioritized. A formulation of drought indices without considering the factors that govern the background state may lead to drought artifacts under a warming climate. Consideration of downscaling techniques, availability of climate data, estimation of potential evapotranspiration (PET), baseline period, non-stationary climate information, and anthropogenic forcing can be additional challenges for a reliable drought assessment under climate change. As one formulation of PET based on temperatures can lead to overestimation of future drying, estimation of PET based on the energy budget framework can be a better approach compared to only temperature-based equations. Although the performance of drought indicators can be improved by incorporating reliable soil moisture estimates, a challenge arises due to limited reliable observed data for verification. Moreover, the uncertainties associated with meteorological forcings in hydrological models can lead to unreliable soil moisture estimates under climate change scenarios.
321 citations
TL;DR: To assess future drought losses, the regional gross domestic product under shared socioeconomic pathways instead of using a static socioeconomic scenario is predicted and increasing precipitation and evapotranspiration patterns are identified for the 1.5 °C and 2.0 °C global warming above the preindustrial at 2020–2039 and 2040–2059, respectively.
Abstract: We project drought losses in China under global temperature increase of 1.5 °C and 2.0 °C, based on the Standardized Precipitation Evapotranspiration Index (SPEI) and the Palmer Drought Severity Index (PDSI), a cluster analysis method, and "intensity-loss rate" function. In contrast to earlier studies, to project the drought losses, we predict the regional gross domestic product under shared socioeconomic pathways instead of using a static socioeconomic scenario. We identify increasing precipitation and evapotranspiration pattern for the 1.5 °C and 2.0 °C global warming above the preindustrial at 2020-2039 and 2040-2059, respectively. With increasing drought intensity and areal coverage across China, drought losses will soar. The estimated loss in a sustainable development pathway at the 1.5 °C warming level increases 10-fold in comparison with the reference period 1986-2005 and nearly threefold relative to the interval 2006-2015. However, limiting the temperature increase to 1.5 °C can reduce the annual drought losses in China by several tens of billions of US dollars, compared with the 2.0 °C warming.
288 citations
10 May 2018
TL;DR: In this article, the effects of greenhouse gas (GHG)-induced global warming may lead to increased surface aridity and more droughts in the twenty-first century due to decreased precipitation in the subtropics and increased evaporative demand associated with higher vapor pressure deficit under warmer temperatures.
Abstract: Many studies have shown that greenhouse gas (GHG)-induced global warming may lead to increased surface aridity and more droughts in the twenty-first century due to decreased precipitation in the subtropics and increased evaporative demand associated with higher vapor pressure deficit under warmer temperatures. Some recent studies argue that increased water use efficiency by plants under elevated CO2 may reduce the evaporative demand and therefore mitigate the drying. Here we first discuss the model-projected changes in precipitation amount and frequency that affect the surface water balance and aridity and then the changes in actual and potential evapotranspiration under GHG-induced warming. The effects of the GHG-induced warming and changes in plants’ physiology under elevated CO2 on precipitation, soil moisture, and runoff are quantified and compared by analyzing different model experiments with and without the physiologic response. The surface drying effect of GHG-induced warming is found to dominate over the wetting effect of plants’ physiology in response to increasing CO2, leading to similar surface drying patterns in climate model simulations with or without the physiologic response in the twenty-first century. Part of the drying comes from increased dry spells (i.e., more dry days) and a flattening of the histograms of drought indices as GHGs increase, with the latter leading to widespread increases in hydrological drought even over areas with increasing mean runoff. Because of this, the change pattern of the mean cannot be used to represent drought changes. Consistent with the projected drying in the twenty-first century, recent analyses of model experiments suggest wetter land surfaces during the last glacial maximum, which implies that dusty air during cold glacial periods may have resulted from other factors, such as stronger winds and more dust sources, rather than drier land surfaces. Finally, the drying in the subtropics does not appear to be just a transient response to increased GHGs, as the warming and precipitation change patterns do not vary significantly over time in 500-year simulations with increased CO2 contents by a fully coupled climate model.
253 citations
References
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01 Jan 2007
TL;DR: The first volume of the IPCC's Fourth Assessment Report as mentioned in this paper was published in 2007 and covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
Abstract: This report is the first volume of the IPCC's Fourth Assessment Report. It covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
32,826 citations
01 Jan 2014
TL;DR: Myhre et al. as discussed by the authors presented the contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) 2013: Anthropogenic and Natural Radiative forcing.
Abstract: This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)
3,684 citations
TL;DR: In this paper, the authors look at observations and model projections from 1923 to 2010, to test the ability of models to predict future drought conditions, which inspires confidence in their projections of drought.
Abstract: Historical records show increased aridity over many land areas since 1950. This study looks at observations and model projections from 1923 to 2010, to test the ability of models to predict future drought conditions. Models are able to capture the greenhouse-gas forcing and El Nino–Southern Oscillation mode for historical periods, which inspires confidence in their projections of drought.
3,385 citations
TL;DR: In this paper, the authors provide a review of fundamental concepts of drought, classification of droughts, drought indices, historical Droughts using paleoclimatic studies, and the relation between DAs and large scale climate indices.
3,352 citations
Earth System Research Laboratory1, University of Colorado Boulder2, Met Office3, National Oceanic and Atmospheric Administration4, ETH Zurich5, University of Bern6, University of East Anglia7, Rovira i Virgili University8, University Corporation for Atmospheric Research9, South African Weather Service10, British Antarctic Survey11, University of Milan12, Norwegian Meteorological Institute13, University of Lisbon14, Environment Canada15, National Center for Atmospheric Research16
TL;DR: The Twentieth Century Reanalysis (20CR) dataset as discussed by the authors provides the first estimates of global tropospheric variability, and of the dataset's time-varying quality, from 1871 to the present at 6-hourly temporal and 2° spatial resolutions.
Abstract: The Twentieth Century Reanalysis (20CR) project is an international effort to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. It is chiefly motivated by a need to provide an observational dataset with quantified uncertainties for validations of climate model simulations of the twentieth century on all time-scales, with emphasis on the statistics of daily weather. It uses an Ensemble Kalman Filter data assimilation method with background ‘first guess’ fields supplied by an ensemble of forecasts from a global numerical weather prediction model. This directly yields a global analysis every 6 hours as the most likely state of the atmosphere, and also an uncertainty estimate of that analysis.
The 20CR dataset provides the first estimates of global tropospheric variability, and of the dataset's time-varying quality, from 1871 to the present at 6-hourly temporal and 2° spatial resolutions. Intercomparisons with independent radiosonde data indicate that the reanalyses are generally of high quality. The quality in the extratropical Northern Hemisphere throughout the century is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging.
It is anticipated that the 20CR dataset will be a valuable resource to the climate research community for both model validations and diagnostic studies. Some surprising results are already evident. For instance, the long-term trends of indices representing the North Atlantic Oscillation, the tropical Pacific Walker Circulation, and the Pacific–North American pattern are weak or non-existent over the full period of record. The long-term trends of zonally averaged precipitation minus evaporation also differ in character from those in climate model simulations of the twentieth century. Copyright © 2011 Royal Meteorological Society and Crown Copyright.
3,043 citations