Geography
Drought
Drought is a prolonged period of abnormally low rainfall, leading to water shortages and environmental stress. It can have significant impacts on agriculture, water supplies, and ecosystems, often resulting in food and water scarcity, economic losses, and social disruption. Droughts can be caused by natural climate variability, such as El Niño events, as well as human activities like overuse of water resources.
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11 Key excerpts on "Drought"
eBook - PDF- James Goff, C. R. de Freitas(Authors)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
Definitions of Drought usually refer to its impacts rather than its causes. A general definition of Drought emphasising impact is ‘a large deviation from normal precipitation for a period long enough to cause soil moisture deficits and reductions in stream flow, severely disturbing normal biological and human activities’. A general definition of Drought stressing cause is ‘a regional deficiency in soil moisture and stream flow caused by either or both lower than normal precipitation and higher than average evapotranspiration’. All definitions refer in one way or another to a deviation from what is considered typical for a given time and place. Consequently, definitions of Drought applicable to climatic regions that are arid or semi-arid are very different from those appropriate for regions with humid tropical or moist mid-latitude climate regimes. As mentioned previously, there are four categories of definitions of Drought: meteorological (or climatological), hydrological, agricultural (or botanical) and socioeconomic. Each one is dealt with in turn in the following sections. Meteorological Drought Meteorological (climatological) definitions of Drought are supply-side definitions. They compare precipitation level to long-term averages and refer to duration of the dry period. The New Zealand Meteorological Service defines ‘absolute Drought’ as a period CHAPTER 3: Drought 37 of at least 15 consecutive days during which no day receives more than 0.2 mm of rain. A more sophisticated definition of a Drought event once used by the New Zealand Ministry of Agriculture and Forestry (now part of the Ministry of Primary Industries) is ‘evapotranspiration exceeding rainfall for a period of 100 days or more’. The Australian Bureau of Meteorology defines Drought as a state of either ‘severe moisture deficiency’ or ‘serious moisture deficiency’ for a period of three months or more. ‘Severe moisture deficiency’ is set down as total rainfall in the lowest 5% of historical totals.
eBook - ePubHandbook of Drought and Water Scarcity
Principles of Drought and Water Scarcity
- Saeid Eslamian, Faezeh A. Eslamian(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
1 Definition of Drought Neil A. Coles University of Leeds and University of Western Australia Saeid Eslamian Isfahan University of Technology1.1Introduction 1.2Defining Drought 1.3Drought and Rainfall Classification 1.4Drought by Design 1.5Summary and Conclusions Authors ReferencesAbstractThe word Drought in its definitive sense is derived from the archaic English and Scottish form of the word “drouth” that is an archaic or dialectal word for thirst. In more recent times, it has been used as a collective term to refer to an acute water shortage rather than thirst specifically.However, the term “Drought” can be applied to the lack or scarcity of anything or a prolonged absence of something specified, but historically it has been used to signify a prolonged period of dryness or low rainfall.This chapter only discusses the use of the term Drought as it relates to water shortages and how it is applied in various instances from forecasting to design.1.1Introduction
Drought is a natural hazard and is one of the least understood and manageable phenomena impacting the world today [30 ]. Vulnerability to Drought is increasing as the global climate varies, human population expands, water resources come under increasing pressure for alternate uses, and people use water in so many different ways and apply alternate demands relative to human consumption (including drinking water and sanitation), industrial uses, agricultural production systems, and environmental requirements such that there is no universal definition of Drought [2 ,11 ,30 ].1.2Defining Drought
Droughts are a normal part of climate variability and are generally recognized around the world as a lack of rainfall; however, this is not the only description that can be applied in defining what a Drought is and the effect it has either locally or regionally. The following definitions of Drought were first introduced in Britain in 1887:
eBook - PDFAgrometeorology
Principles and Applications of Climate Studies in Agriculture
- Harpal S. Mavi, Graeme J. Tupper(Authors)
- 2004(Publication Date)
- CRC Press(Publisher)
People experience shock, anger, and denial (Cheryl, 2000). The environmental cost may be in the form of damage to wildlife, wind erosion, higher concentrations of salt and pollutants in water, and de-cay of vegetation. 95 96 AGROMETEOROLOGY DEFINITION OF Drought The definition of Drought is not very simple, and the question “What is Drought?” continues to pose a problem (Sivakumar, 1991). This is because Drought could mean different things to different people, and there are proba-bly as many definitions of Drought as there are users of water. In general, a Drought is when a shortfall in precipitation creates a shortage of water, whether it is for crops, utilities, municipal water supply, recreation, wildlife, or other purposes. According to a WMO definition (Bogardi et al., 1994), “Drought is a sustained, extended deficiency in precipitation.” Operational definitions of Drought vary from place to place and are cru-cial to identify the beginning and intensity of Drought. There are three main types of Drought: meteorological, agricultural, and hydrological (National Drought Mitigation Center, 1996c). 1. Meteorological Drought is an expression of rainfall departure from normal over some period of time. Meteorological Drought definitions are usually region specific and are based on a thorough understanding of the climatology of the region. 2. Agricultural Drought occurs when there is not enough soil moisture to meet the needs of crops at a particular time. 3. Hydrological Drought refers to deficiencies in surface and subsurface water supplies. It is measured as stream flow and as lake, reservoir, and groundwater levels. Some economists look at Drought in socioeconomic terms. According to them, a socioeconomic Drought is when physical water shortages start to af-fect supply and demand of goods. METEOROLOGICAL INDICATORS OF Drought Drought conditions are basically due to a deficit of water supply in time and/or space.
eBook - PDFHydrology and Hydroclimatology
Principles and Applications
- M. Karamouz, S. Nazif, M. Falahi(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
599 12 Drought Analysis and Management 12.1 INTRODUCTION Drought is a normal, recurrent feature of climate, although many people think that it is a rare and random event. Drought happens in any climate condition even though its characteristics may be completely different in different regions. Drought is a temporary deviation from normal weather condition and it is different from aridity. Aridity refers to the low rainfall regions and is a permanent feature of climate. Drought originates from a deficiency of precipitation over an extended period of time. Drought should be considered relative to some long-term average condition of balance between precipita-tion and evapotranspiration in a particular area, a condition often perceived as “normal.” It is also related to the timing (i.e., principal season of occurrence, delays in the start of the rainy season, occurrence of rains in relation to principal crop growth stages) and the effectiveness (i.e., rainfall intensity, number of rainfall events) of the rains. Other climatic factors such as high temperature, high wind, and low relative humidity are often associated with it in many regions of the world and can significantly aggravate its severity. Based on the hydrologic components that are affected by Drought consequences, different types of Drought are distinguished, including meteorological, hydrologic, and agricultural Drought. Meteorological Drought is related to deficiency in precipitation. Hydrologic and agricultural Droughts are related to deficit in water resources and soil moisture, respectively. The analysis of Drought severity and magnitude is highly dependent on its type and different indices are employed in each case. Drought is beyond just a physical phenomenon or natural event. Its impacts on society result from the interplay between natural event water resources (less than least expected precipitation resulting from natural climatic variability) and the demand people place on water supply.
eBook - ePubDrought and Aquatic Ecosystems
Effects and Responses
- P. Sam Lake(Author)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
In the natural state, hydrological Drought is induced by shortfalls in precipitation affecting surface runoff and groundwater storage of water. However, it may be induced not only by precipitation deficits, but also by water deficits created by human land use and water storage (NDMC, 2005; Wilhite & Buchanan-Smith, 2005). The state of the catchment in terms of such factors as dryness, plant cover and soil porosity may strongly influence the onset of hydrological Drought.Agricultural Drought ‘is typically defined as a period when soil moisture is inadequate to meet evapotranspirative demands so as to initiate and sustain crop growth’ (Changnon, 1987). As such, it focuses on ‘soil moisture deficits and differences between actual and potential evapotranspiration’ (Tate & Gustard, 2002) and is primarily centred on the availability of soil moisture in the root zone of crops, though it may also refer to lack of water for plant growth to meet the needs of livestock (Changnon, 1987). Agricultural Drought is concerned with soil moisture so, while it dependent on rainfall, it is also strongly influenced by factors that govern water infiltration and soil water-holding capacity (Wilhite & Buchanan-Smith, 2005).As agricultural Drought is primarily concerned with crop growth, Drought related to non-agricultural terrestrial biota is not covered by indices for agricultural Drought. One could expect the terrestrial biota native to an area to be better able to deal with Drought than exotic and domestic plants and animals.Ecological Drought has been recognized only recently. It has been defined as ‘a shortage of water causing stress on ecosystems, adversely affecting the life of plants and animals’ (Tallaksen & van Lanen, 2004). However, unlike agricultural Drought, ecological Drought currently lacks specific indices to quantify it.Socioeconomic or operational Drought depends basically on the availability of water for human activities, so this form of Drought varies greatly with locality, human demand and with the level of infrastructure for water capture, storage and delivery (Mawdsley et al
eBook - PDFClimate and Human Migration
Past Experiences, Future Challenges
- Robert A. McLeman(Author)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
144 Drought and Its influence on Migration countries (Kentayash and Dracup 2002). It is not essential to understand the workings of these various Drought indices to investigate the influence of Droughts on human migration, but a familiarity with them is helpful for those seeking to take model-based projections of future Droughts under climate change and assess their potential impacts on food supplies, population movements, and other aspects of human well-being. Hydrological Drought refers to shortages in the available supply of water in all potential locations across a given area, including natural features on the surface (e.g. streams, rivers, and wetlands), in the ground, and in human-constructed features like canals and reservoirs (Nalbantis and Tsakiris 2009). Precise measures of the amount of water present in a watershed at a particular time are virtually impossible given the enormous amounts of data and sampling points required. The availability of ground- water is especially challenging to measure, and shortfalls in groundwater often linger well after precipitation and surface water levels have returned to normal (Shahid and Hazarika 2010). Hydrological Drought is typically recognized by observing changes in stream flow over time, by using gauges situated at critical points within a water- shed, and by monitoring water levels in storage reservoirs. The ability to recognize and generate future predictions of hydrological Drought is particularly important for areas of chronic water stress (i.e. where the size of the population is very high rela- tive to available potable water supplies). In recent years, cities including Atlanta, Mumbai, and Sana’a (Yemen) have come perilously close to exhausting their water supplies during hydrological Droughts (Associated Press 2007, Deccan Herald 2012, IRIN 2012).
eBook - PDFMitigating Droughts and Floods in Agriculture
Policy Lessons and Approaches
- (Author)
- 2016(Publication Date)
- IWA Publishing(Publisher)
Box 1.1. Defining Droughts and floods There are a large number of definitions of Droughts and floods, from more abstract to more concrete, from more descriptive to more operational. Droughts and floods are indeed an object of study in a variety of disciplines such as meteorology, hydrology, agronomy, economics, sociology, psychology, and political science among others. In practice, water managers and policy makers need to rely on working definitions to plan their programmes and pilot their interventions in the course of action. Economists aim at measuring the costs of Droughts and floods, which requires a different approach and eventually different indicators. Sociologists focus on topics such as the collective response to extreme events, such as crisis management. Definitions may therefore vary depending on objectives, local conditions and socio-economic contexts. There is no “one size fits all” definition of either Droughts or floods. Notwithstanding these complexities, Droughts can be broadly defined as a temporary decrease of water availability in a given water system, caused by prolonged deviations from average levels precipitation. Drought essentially “differs from other natural disasters in the slowness of onset and its usual lengthy duration”, which makes it difficult to determine the onset and duration of a Drought event (European Commission, 2007; Wilhite, 2007). Drought is a normal and recurrent feature of climate, although it can evolve under certain circumstances into a disaster, depending mainly on the vulnerability of the affected society and its capacity to manage the impacts, and on the severity and duration of the event (Kampragou et al., 2011). From a general point of view, floods can be defined as “rises, usually brief, in the water level of a stream or water body to a peak from which the water level recedes at a slower rate” (WMO and UNESCO, 2012).
eBook - ePubDrought
Science and Policy
- Ana Iglesias, Dionysis Assimacopoulos, Henny A.J. Van Lanen, Ana Iglesias, Dionysis Assimacopoulos, Henny A.J. Van Lanen(Authors)
- 2018(Publication Date)
- Wiley-Blackwell(Publisher)
Journal of Hydrology 526: 208–220.- Wilhite, D.A. (Ed.) (2000). Droughts as a natural hazard: concepts and definitions. In:
Drought, A Global Assessment, Vol I and II, Routledge Hazards and Disasters Series. London: Routledge.- Yevjevich, V. (1967). An objective approach to definition and investigations of continental hydrologic Droughts. Hydrology Papers 23, Colorado State University, Fort Collins, USA.
- Zelenhasic, E. and Salvai, A. (1987). A method of streamflow Drought analysis.
Water Resources Research23 (1): 156–168.
Passage contains an image 1.2 Recent Trends in Historical Drought
Kerstin Stahl1 Lena M. Tallaksen2 and Jamie Hannaford31 University of Freiburg, Freiburg, Germany2 University of Oslo, Oslo, Norway3 Centre for Ecology and Hydrology, Wallingford, United Kingdom1.2.1 Introduction
Drought is caused by climate anomalies. Combined with low antecedent storage in surface and subsurface systems, these may lead to water deficit in the hydrological cycle, and thus to hydrological Drought (e.g. Tallaksen and Van Lanen, 2004 ; Tallaksen et al., 2015 ). Trends in hydrological Drought – as typically characterised by deficits in streamflow or groundwater – are thus important indicators of changes in water availability. For policy development and water management at international scales, these large‐scale trends in water availability can provide crucial information. Recent years have witnessed a number of severe Droughts in different regions across Europe. These events have prompted numerous national and regional studies on past trends, and projected future changes, in Drought – as summarised by Stahl et al. (2014 ). Particular concerns are the impacts of extremely low streamflow on aquatic ecology and a variety of human water uses, such as for water supply, energy production, waterborne transportation, industrial use, etc. (Stahl et al., 2016
eBook - PDF- Hazem Shawky Fouda(Author)
- 2019(Publication Date)
- Delve Publishing(Publisher)
Since agriculture is a major economic sector of the economy of Africa, one would logically expect major population concentrations to be in the main agricultural regions as is the case in the region. It is due to this dependent of the economy on agriculture that rainfall becomes a major actor in the economic planning of African region. Any rainfall anomaly in the rainfall distribution and amount in the high potential lands and to a smaller extent in the medium potential lands of the region is bound to have a telling implication on the region’s economy. One such rainfall anomaly that has become a major problem in the agricultural lands in Africa is Drought. 1.2. DEFINITION OF Drought Drought is a meteorological phenomenon, which is very difficult to define and predict. In most parts of the Africa and the rest of world, Drought condition has resulted in lack of appropriate management strategies thus leading to disastrous effects like famine and desertification. Drought condition constitutes a lot of disciplinary dispute but its occurrence has been part of human history from time manorial as long as some kind of agriculture existed. Due to lack of universally accepted definition of Drought, it has been very difficult to give its causes especially as concerns the immediate and ultimate cause. Also lack of definition plus the creeping nature of Drought has made it difficult to determine the start and end of Drought period. Drought as a factor in resource planning and management is only important where there is some kind of human activity or where the activities in an area affects human activities. Since Africa is one of the most agriculturally productive and one of the most populous regions in the world, it is wise to check its meteorological condition during the so-called Drought period in order to know its vulnerability to Drought occurrence. It is also important to have proper Drought management strategies and in this case,
eBook - PDFDrought
Detection and Solutions
- Gabrijel Ondrasek(Author)
- 2020(Publication Date)
- IntechOpen(Publisher)
Hydrological Droughts can be defined as the scarcity of surface and subsurface water resources that leads to negative effects in water resources management system. In this regard, our results indicate that the annual runoff seems to be a good variable to identify hydrological Droughts, showing an especial good agreement with the SPEI-12. The agreement between variables shown here also evidences that the SPEI is an adequate index to investigate Drought conditions over the IP, reproducing these in a similar way than other Drought-related variables over the study period. This is of high relevance to adequately develop strategies to mitigate the effects of Droughts in the future. Acknowledgements This study has been financed by the Spanish Ministry of Economy and Competitiveness, with additional support from the European Community fund (FEDER), project CGL2013-48539-R and CGL2017-89836-R. The WRF simulation was run in the ALHAMBRA supercomputer infrastructure (https://alhambra.ugr. es). The ERA-Interim data were obtained from ECMWF portal and the WRF model from NCAR. Conflict of interest The authors declare that the research was conducted in absence of any potential conflict of interest. Author details Matilde García-Valdecasas Ojeda*, Emilio Romero Jiménez, Sonia R. Gámiz-Fortis, Yolanda Castro-Díez and María Jesús Esteban Parra Department of Applied Physics, University of Granada, Granada, Spain *Address all correspondence to: [email protected] 144 Drought - Detection and Solutions References [1] Whilite DA. Drought as a natural hazard: Concepts and definitions. In: Whilite DA, editor. Drought: A Global Assessment. London: Routledge; 2010. pp. 3-18 [2] Sheffield J, Wood EF. Projected changes in Drought occurrence under future global warming from multi-model, multi-scenario, IPCC AR4 simulations. Climate Dynamics. 2008; 31 :79-105. DOI: 10.1007/ s00382-007-0340-z [3] Dai A. Drought under global warming: A review.
eBook - PDFDivided Environments
An International Political Ecology of Climate Change, Water and Security
- Jan Selby, Gabrielle Daoust, Clemens Hoffmann(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
Modern transport and communications infrastructures can, when necessary – though also, of course, with significant hardship and suffering – usually facilitate escape from protracted Drought conditions; migration in this sense is thus a critical means of adaptation to environmental shocks. 37 And, in a post-colonial international political system where mass starvation is not as easily ignored or hidden as previously, national and international systems of Drought monitoring and response serve as powerful safety nets against Drought impacts. Ultimately, in a world where the speeds of move- ment, exchange and communication have so radically increased, Droughts are no longer short-term shock events but protracted socio-ecological 36 de Waal, ‘The end of famine?’, 184–5; FAO et al., The State of Food Security and Nutrition in the World 2019: Safeguarding against Economic Slowdowns and Downturns (2019), 3–26; CRED, EM-DAT data; de Waal, ‘Famine mortality’. 37 R. Black et al., ‘Migration as adaptation’, Nature, 478 (2011), 447–9. A Brief History of Drought 93 crises, such that adaptation and impact mitigation are, though painful, typically possible. Storm surges and flash floods typically strike with little warning, visiting immense destruction on all in their paths. The same, however, does not apply to Droughts. The point here, to avoid any doubt, is neither that the global trend of reduced Drought vulnerability is universal, inevitable or even linear, nor that Drought is rendered irrelevant by them. Some places and groups, especially politically excluded ethnic groups and women, are much more vulnerable to Drought than others. Agriculture-dependent economies tend to be more vulnerable, while more developed and diversified econo- mies are less so: hence north-east Syria was more affected by the 2006/7– 2008/9 eastern Mediterranean Drought than the rest of the country and Syria more affected than Cyprus (or than Israel would have been had the Drought also struck there).
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