Recent drought and precipitation tendencies in Ethiopia
TL;DR: In this article, a monthly precipitation data set for 14 homogeneous rainfall zones was constructed based on 174 gauges, and the standardized precipitation index was calculated on seasonal, annual, and biannual time scales.
Abstract: In 2011, drought in the Horn of Africa again made news headlines. This study aims to quantify the meteorological component of this and other drought episodes in Ethiopia since 1971. A monthly precipitation data set for 14 homogeneous rainfall zones was constructed based on 174 gauges, and the standardized precipitation index was calculated on seasonal, annual, and biannual time scales. The results point to 2009 as a year of exceptionally widespread drought. All zones experienced drought at the annual scale, although in most zones, previous droughts were more extreme. Nationally, 2009 was the second driest year, surpassed only by the historic year 1984. Linear regression analysis indicates a precipitation decline in southern Ethiopia, during both February–May and June–September. In central and northern Ethiopia, the analysis did not provide evidence of similar tendencies. However, spring droughts have occurred more frequently in all parts of Ethiopia during the last 10–15 years.
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TL;DR: A review of the current state of scientific knowledge of definitions, processes, and quantification of hydrological drought is given in this paper, where the influence of climate and terrestrial properties (geology, land use) on hydrologic drought characteristics and the role of storage is discussed.
Abstract: Drought is a complex natural hazard that impacts ecosystems and society in many ways. Many of these impacts are associated with hydrological drought (drought in rivers, lakes, and groundwater). It is, therefore, crucial to understand the development and recovery of hydrological drought. In this review an overview is given of the current state of scientific knowledge of definitions, processes, and quantification of hydrological drought. Special attention is given to the influence of climate and terrestrial properties (geology, land use) on hydrological drought characteristics and the role of storage. Furthermore, the current debate about the use and usefulness of different drought indicators is highlighted and recent advances in drought monitoring and prediction are mentioned. Research on projections of hydrological drought for the future is summarized. This review also briefly touches upon the link of hydrological drought characteristics with impacts and the issues related to drought management. Finally, four challenges for future research on hydrological drought are defined that relate international initiatives such as the Intergovernmental Panel on Climate Change (IPCC) and the ‘Panta Rhei’ decade of the International Association of Hydrological Sciences (IAHS). WIREs Water 2015, 2:359–392. doi: 10.1002/wat2.1085
For further resources related to this article, please visit the WIREs website.
805 citations
TL;DR: In this paper, the authors examined several aspects of the climate of eastern Africa and found that the long rains have been declining continuously in recent decades, and that the Madden-Julian Oscillation has emerged as a factor in interannual and intraseasonal variability.
Abstract: This review examines several aspects of the climate of eastern Africa. The climatic commonality throughout the region is the frequent occurrence of drought severe enough to incapacitate the population. Because of recent droughts and evidence of disastrous, long-term climatic change, the region has become a major focus of meteorological research. This review covers six relevant topics: climatic regionalization, seasonal cycle, intraseasonal variability, interannual variability, recent trends, and seasonal forecasting. What emerges is a markedly different view of the factors modulating rainfall, the dynamics associated with the seasons, and the character of teleconnections within the region and the interrelationships between the various rainy seasons. Some of the most important points are the following. (1) The paradigm of two rainy seasons resulting from the biannual equatorial passage of the Intertropical Convergence Zone is inadequate. (2) The “long rains” should not be treated as a single season, as character, causal factors, and teleconnections are markedly different in each month. (3) The long rains have been declining continuously in recent decades. (4) The Madden-Julian Oscillation has emerged as a factor in interannual and intraseasonal variability, but the relative strength of Pacific and Indian Ocean anomalies plays a major role in the downward trend. (5) Factors governing the short rains are nonstationary. (6) Droughts have become longer and more intense and tend to continue across rainy seasons, and their causes are not adequately understood. (7) Atmospheric variables provide more reliable seasonal forecasts than the factors traditionally considered in forecast models, such as sea surface temperatures and El Nino–Southern Oscillation.
367 citations
TL;DR: In this paper, a trend analysis has been employed to inspect the change of rainfall and temperature in northcentral Ethiopia using gridded monthly precipitation data obtained from Global Precipitation and Climate Centre (GPCC V7) and temperature data from Climate Research Unit (CRU TS 3.23) with 0.5° by 0.1° resolution from 1901 to 2014.
Abstract: Examining the spatiotemporal dynamics of meteorological variables in the context of changing climate, particularly in countries where rainfed agriculture is predominant, is vital to assess climate-induced changes and suggest feasible adaptation strategies. To that end, trend analysis has been employed to inspect the change of rainfall and temperature in northcentral Ethiopia using gridded monthly precipitation data obtained from Global Precipitation and Climate Centre (GPCC V7) and temperature data from Climate Research Unit (CRU TS 3.23) with 0.5° by 0.5° resolution from 1901 to 2014. Data have been analyzed using coefficient of variation, anomaly index, precipitation concentration index and Palmer drought severity index. Furthermore, Mann-Kendall test was used to detect the time series trend. The result revealed intra- and inter-annual variability of rainfall while Palmer drought severity index value proved the increasing trend of the number of drought years. Annual, belg and kiremt rainfall have decreased with a rate of 15.03, 1.93 and 13.12 mm per decade respectively. The declining trend for annual and kiremt rainfall was found to be statistically significant while that of belg was not significant. The rate of change of temperature was found to be 0.046, 0.067 and 0.026 °C per decade for mean, minimum and maximum respectively. The Mann-Kendall trend analysis test result revealed increasing trend for mean and minimum average temperatures through time significantly while the trend for maximum temperature exhibited a non-significant increasing trend. We recommend strategies designed in the agricultural sector have to take the declining and erratic nature of rainfall and increasing trend of temperature into consideration.
339 citations
National Oceanic and Atmospheric Administration1, University of New South Wales2, University of Oxford3, University of Málaga4, Complutense University of Madrid5, University of Melbourne6, National Institute of Water and Atmospheric Research7, Centre national de la recherche scientifique8, Chinese Academy of Sciences9, China Meteorological Administration10, Met Office11, Royal Netherlands Meteorological Institute12, University of Edinburgh13, Stanford University14, Natural Environment Research Council15, University of California, Santa Barbara16, University of Tokyo17, Oregon University System18, University of Lisbon19
TL;DR: In this paper, 19 analyses by 18 different research groups, often using quite different methodologies, of 12 extreme events that occurred in 2012 are presented, and the differences also provide insights into the structural uncertainty of event attribution, the uncertainty that arises directly from the differences in analysis methodology.
Abstract: Attribution of extreme events is a challenging science and one that is currently undergoing considerable evolution. In this paper are 19 analyses by 18 different research groups, often using quite different methodologies, of 12 extreme events that occurred in 2012. In addition to investigating the causes of these extreme events, the multiple analyses of four of the events, the high temperatures in the United States, the record low levels of Arctic sea ice, and the heavy rain in northern Europe and eastern Australia, provide an opportunity to compare and contrast the strengths and weaknesses of the various methodologies. The differences also provide insights into the structural uncertainty of event attribution, that is, the uncertainty that arises directly from the differences in analysis methodology. In these cases, there was considerable agreement between the different assessments of the same event. However, different events had very different causes. Approximately half the analyses found some evidence that anthropogenically caused climate change was a contributing factor to the extreme event examined, though the effects of natural fluctuations of weather and climate on the evolution of many of the extreme events played key roles as well.
315 citations
TL;DR: In this paper, the authors used the outputs of three workshops and also included post-workshop analyses to assess the changes of climate extremes within the Greater Horn of Africa (GHA) region using observed in situ data running from 1971 to 2006.
Abstract: Recent special reports on climate extremes have shown evidences of changes in the patterns of climate extremes at global, regional and local scales. Understanding the characteristics of climate extremes at regional and local levels is critical not only for the development of preparedness and early warning systems, but is also fundamental in the development of any adaptation strategies. There is still very limited knowledge regarding the past, present and future patterns of climate extremes in the Greater Horn of Africa (GHA). This study, which was supported by the World Bank Global Facility for Disaster Reduction and Recovery (WB-GFDRR) and implemented by the World Meteorological Organization, was organized in terms of three workshops with three main objectives; (1) analysis of daily rainfall and temperature extremes for ten countries in the GHA region using observed in situ data running from 1971 to 2006, (2) assessing whether the United Kingdom Met-office and Hadley centre Providing REgional Climates for Impact Studies (UK-PRECIS) modelling system can provide realistic representation of the past and present climate extremes as observed by available in situ data, and (3) studying the future regional climate extremes under different scenarios to further assess the expected changes in climate extremes. This paper, therefore, uses the outputs of these workshops and also includes post-workshop analyses to assess the changes of climate extremes within the GHA. The results showed a significant decrease in total precipitation in wet days greater than 1 mm and increasing warm extremes, particularly at night, while cold extremes are decreasing. Considering a combination of geophysical models and satellite gravimetry observations from the Gravity Recovery and Climate Experiment (GRACE) mission in the frame of GRACE daily Kalman-smoothing models, for the years 2002 to 2010, we explored a decline in total water storage variations over the GHA.
218 citations
References
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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
"Recent drought and precipitation te..." refers background or methods in this paper
...Drought begins when the SPI first falls below zero and ends with the first positive value (McKee et al. 1993)....
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...2.3 Classifying drought using the standardized precipitation index The SPI (as described by McKee et al. 1993) was used to define drought periods....
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...Monthly precipitation for each zone was calculated for 1972–2011, and the standardized precipitation index (McKee et al. 1993) was used to identify droughts during this period....
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...Precipitation is normally not normally distributed, and McKee et al. (1993) proposed a simple solution to this problem by applying a gamma transformation to the distribution....
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...McKee et al. (1993) recommended using record containing at least 30 years of data when calculating the SPI....
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TL;DR: The Global Precipitation Climatology Project (GPCP) version 2 Monthly Precise Analysis as discussed by the authors is a merged analysis that incorporates precipitation estimates from low-orbit satellite microwave data, geosynchronous-orbit-satellite infrared data, and rain gauge observations.
Abstract: The Global Precipitation Climatology Project (GPCP) Version 2 Monthly Precipitation Analysis is described. This globally complete, monthly analysis of surface precipitation at 2.5 degrees x 2.5 degrees latitude-longitude resolution is available from January 1979 to the present. It is a merged analysis that incorporates precipitation estimates from low-orbit-satellite microwave data, geosynchronous-orbit-satellite infrared data, and rain gauge observations. The merging approach utilizes the higher accuracy of the low-orbit microwave observations to calibrate, or adjust, the more frequent geosynchronous infrared observations. The data set is extended back into the premicrowave era (before 1987) by using infrared-only observations calibrated to the microwave-based analysis of the later years. The combined satellite-based product is adjusted by the raingauge analysis. This monthly analysis is the foundation for the GPCP suite of products including those at finer temporal resolution, satellite estimate, and error estimates for each field. The 23-year GPCP climatology is characterized, along with time and space variations of precipitation.
4,951 citations
"Recent drought and precipitation te..." refers methods in this paper
...The discrepancy between the gauge-based zone data described in this study and the satellite-based, gauge-adjusted GPCP data set may have several causes....
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...As there are large local variations in rainfall in Ethiopia, the quality of the GPCP and similar data sets is lower than it would have been if more ground observations had been included (Dinku et al. 2007)....
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...Data from the Global Precipitation Climatology Project (GPCP) (Adler et al. 2003; Huffman et al. 2009) was used for comparison with the zone data in selected years....
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...As the rank map in the lower left corner shows, 2009 was the driest or second driest year in most of Ethiopia in the GPCP data; more severe than both 1984 and 2002....
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...SPI values based on the GPCP data set demonstrate quite distinct patterns for these 3 years....
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4,200 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
"Recent drought and precipitation te..." refers background in this paper
...During the northern hemisphere summer, air masses from the Indian Ocean, Central Africa, and the Red Sea region flow toward Ethiopia (Mohamed et al. 2005; Korecha and Barnston 2007; Levin et al., 2009; Segele et al. 2009; Viste and Sorteberg 2011)....
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TL;DR: In this article, the power of the Mann-Kendall test and Spearman's rho test for detecting monotonic trends in time series data is investigated by Monte Carlo simulation.
1,642 citations
"Recent drought and precipitation te..." refers result in this paper
...As the power of these tests in detecting trends is similar (Yue et al. 2002), and no practical differences between them appeared in our results, only the outcome of Spearman's rho test will be shown....
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