A Multiscalar Drought Index Sensitive to Global Warming: The Standardized Precipitation Evapotranspiration Index
TL;DR: In this article, a new climatic drought index, the standardized precipitation evapotranspiration index (SPEI), is proposed, which combines multiscalar character with the capacity to include the effects of temperature variability on drought assessment.
Abstract: The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an...
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TL;DR: In this article, a commonly used drought index and observational data are examined to identify the cause of these discrepancies, and the authors indicate that improvements in the quality and coverage of precipitation data and quantification of natural variability are necessary to provide a better understanding of how drought is changing.
Abstract: Recent studies have produced conflicting results about the impacts of climate change on drought. In this Perspective, a commonly used drought index and observational data are examined to identify the cause of these discrepancies. The authors indicate that improvements in the quality and coverage of precipitation data and quantification of natural variability are necessary to provide a better understanding of how drought is changing.
2,144 citations
TL;DR: It is argued that contextual cues should be used as part of deep learning to gain further process understanding of Earth system science problems, improving the predictive ability of seasonal forecasting and modelling of long-range spatial connections across multiple timescales.
Abstract: Machine learning approaches are increasingly used to extract patterns and insights from the ever-increasing stream of geospatial data, but current approaches may not be optimal when system behaviour is dominated by spatial or temporal context. Here, rather than amending classical machine learning, we argue that these contextual cues should be used as part of deep learning (an approach that is able to extract spatio-temporal features automatically) to gain further process understanding of Earth system science problems, improving the predictive ability of seasonal forecasting and modelling of long-range spatial connections across multiple timescales, for example. The next step will be a hybrid modelling approach, coupling physical process models with the versatility of data-driven machine learning.
2,014 citations
TL;DR: In this article, the authors identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively and present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter Droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter Drought, consistent with fundamental physiology; (5) shorter Drought can become lethal under warming, increasing the frequency of lethal Drought; and (6) mortality happens rapidly
Abstract: Patterns, mechanisms, projections, and consequences of tree mortality and associated broad-scale forest die-off due to drought accompanied by warmer temperatures—“hotter drought”, an emerging characteristic of the Anthropocene—are the focus of rapidly expanding literature. Despite recent observational, experimental, and modeling studies suggesting increased vulnerability of trees to hotter drought and associated pests and pathogens, substantial debate remains among research, management and policy-making communities regarding future tree mortality risks. We summarize key mortality-relevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated [CO2] and increased water-use efficiency; observed and modeled increases in forest growth and canopy greening; widespread increases in woody-plant biomass, density, and extent; compensatory physiological, morphological, and genetic mechanisms; dampening ecological feedbacks; and potential mitigation by forest management. In contrast, recent studies document more rapid mortality under hotter drought due to negative tree physiological responses and accelerated biotic attacks. Additional evidence suggesting greater vulnerability includes rising background mortality rates; projected increases in drought frequency, intensity, and duration; limitations of vegetation models such as inadequately represented mortality processes; warming feedbacks from die-off; and wildfire synergies. Grouping these findings we identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively. We also present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter drought, consistent with fundamental physiology; (5) shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly; and (6) mortality happens rapidly relative to growth intervals needed for forest recovery. These high-confidence drivers, in concert with research supporting greater vulnerability perspectives, support an overall viewpoint of greater forest vulnerability globally. We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events. Given the profound ecological and societal implications of underestimating global vulnerability to hotter drought, we highlight urgent challenges for research, management, and policy-making communities.
1,786 citations
Cites background from "A Multiscalar Drought Index Sensiti..."
...Essentially all locations will experience extreme drought and heat events sooner or later (Palmer 1965, Vicente-Serrano et al. 2010, IPCC 2012, Jenerette et al. 2012)....
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...Droughts essentially happen everywhere eventually due the combination of inherent climate variability and the site-specific relative nature of drought (Palmer 1965, Vicente-Serrano et al. 2010, Jenerette et al. 2012), and substantial global warming is a consensus climate projection (IPCC 2013)....
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01 Apr 2012
1,699 citations
TL;DR: In this paper, the authors present a collection of 25 figs from the genus "Figs" and discuss the relationship between the two types of figs: figs and figs.
Abstract: 48 pags., 25 figs. Available online 21 December 2013. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1097-0088
1,083 citations
Cites background or methods from "A Multiscalar Drought Index Sensiti..."
...We previously showed that the log-logistic distribution provided better results than other distributions for obtaining SPEI series in standardized z units (mean = 0, SD = 1) (Vicente-Serrano et al., 2010a)....
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...…average soil water and ETa did not show substantial differences between the periods, and that this stress had measurable consequences in the vegetation of this semi-arid region, as described in several recent ecological studies (Vicente-Serrano et al., 2010c, 2012a, 2012b; Camarero et al., 2012)....
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...The standardized precipitation evapotranspiration index (SPEI) was first proposed by Vicente-Serrano et al. (2010a) as an improved drought index that is especially suited for studies of the effect of global warming on drought severity....
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...Vicente-Serrano et al. (2010a, 2010b, 2011a, 2011b, 2012a) provided complete descriptions of the theory behind the SPEI, the computational details, and comparisons with other popular drought indicators such as the PDSI (Palmer, 1965) and the SPI (McKee et al., 1993)....
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...Thus, we computed SPEI series by three methods based on data from eleven observatories around the world (see details in Vicente-Serrano et al., 2010a)....
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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
Book•
01 Jan 1998
TL;DR: In this paper, an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients is presented, based on the FAO Penman-Monteith method.
Abstract: (First edition: 1998, this reprint: 2004). This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in FAO Irrigation and Drainage Paper No. 24, Crop water requirements, in 1977, allows estimation of the amount of water used by a crop, taking into account the effect of the climate and the crop characteristics. The publication incorporates advances in research and more accurate procedures for determining crop water use as recommended by a panel of high-level experts organised by FAO in May 1990. The first part of the guidelines includes procedures for determining reference crop evapotranspiration according to the FAO Penman-Monteith method. These are followed by updated procedures for estimating the evapotranspiration of different crops for different growth stages and ecological conditions.
21,958 citations
01 Jan 1993
TL;DR: The definition of drought has continually been a stumbling block for drought monitoring and analysis as mentioned in this paper, mainly related to the time period over which deficits accumulate and to the connection of the deficit in precipitation to deficits in usable water sources and the impacts that ensue.
Abstract: 1.0 INTRODUCTION Five practical issues become important in any analysis of drought. These include: 1) time scale, 2) probability, 3) precipitation deficit, 4) application of the definition to precipitation and to the five water supply variables, and 5) the relationship of the definition to the impacts of drought. Frequency, duration and intensity of drought all become functions that depend on the implicitly or explicitly established time scales. Our experience in providing drought information to a collection of decision makers in Colorado is that they have a need for current conditions expressed in terms of probability, water deficit, and water supply as a percent of average using recent climatic history (the last 30 to 100 years) as the basis for comparison. No single drought definition or analysis method has emerged that addresses all these issues well. Of the variety of definitions and drought monitoring methods used in the past, by far the most widely used in the United States is the Palmer Drought Index (Palmer, 1965), but its weaknesses (Alley, 1984) frequently limit its wise application. For example, time scale is not defined for the Palmer Index but does inherently exist. The definition of drought has continually been a stumbling block for drought monitoring and analysis. Wilhite and Glantz (1985) completed a thorough review of dozens of drought definitions and identified six overall categories: meteorological, climatological, atmospheric, agricultural, hydrologic and water management. Dracup et al. (1980) also reviewed definitions. All points of view seem to agree that drought is a condition of insufficient moisture caused by a deficit in precipitation over some time period. Difficulties are primarily related to the time period over which deficits accumulate and to the connection of the deficit in precipitation to deficits in usable water sources and the impacts that ensue.
6,514 citations
"A Multiscalar Drought Index Sensiti..." refers background or methods in this paper
...…related to drought analysis and monitoring systems have been conducted using either 1) the Palmer drought severity index (PDSI; Palmer 1965), based on a soil water balance equation, or 2) the standardized precipitation index (SPI; McKee et al. 1993), based on a precipitation probabilistic approach....
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...McKee et al. (1993) clearly illustrated this essential characteristic of droughts through the consideration of usable water resources, including soil moisture, groundwater, snowpack, river discharges, and reservoir storages....
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6,391 citations
4,207 citations