Review of Hydrological Drought Analysis Status in Ethiopia

Abstract

Drought is a complex natural disaster unlike flood, which covers a large area when it occurred. This review was conducted on hydrological drought analysis and monitoring status in Ethiopia by reviewing the master plan of eight major river basins and previous research related to drought. A total of 24 article papers was reviewed and it is found that hydrological drought analysis studies cover only 8.33% of all of the river basins in Ethiopia. Researchers in the region have focused primarily on meteorological drought (37.5%) rather than hydrological and agricultural drought analysis. Although Ethiopia has long been dependent on rainfed agriculture for its economy and remains the primary livelihood of the population, the Ethiopian government has begun focusing on transitioning to an industrial economy, placing pressure on the water resource. In a region plagued by drought, drought analysis, and monitoring, drought early warning systems and effective mitigation measures are still limited and even lacking in some areas. Therefore, emphasis on hydrological drought analysis and development of suitable drought mitigation measurements is important to implement strategies for effective and sustainable water resource management by which water may remain available during the long dry seasons and the impacts of hydrological drought may be lessened.

1. Introduction

Drought is a worldwide natural hazard and has a detrimental impact on society, the environment, and the economy [1]. Extreme hydrological events both high (flood) and low (drought) flow are of particular concern globally. Of these hydrological extremes, drought is the most complex and widespread [2]. It is one of the most common natural events that has devastating negative impacts on agriculture and water resources [3].

There is no universal definition for drought due to its complexity [4]. Therefore, meteorologists defined drought as a scarcity of precipitation [5, 6, 7, 8, 9, 10]; hydrologists have defined hydrological drought as scarcity of surface and subsurface water [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]; agriculturalists and agronomists defined agricultural drought as related to soil moisture deficiency [3, 16, 17] and sociologists and economists defined the overall welfare crisis of the society caused by drought to be socioeconomical drought [4, 18, 19, 20, 21]. These types of droughts have accumulating effects, thus meteorological drought results in losses, such as crop stress, predation by pests, and disease due to low moisture, to the agricultural systems while hydrological drought causes the shortage of water supply, decrease in reservoir water level and groundwater volume, lower irrigation and hydropower production [14]. The accumulation of meteorological and hydrological drought results in socioeconomical drought in which the overall ecosystem will be disturbed and human and animal lives will be negatively impacted and even lost [15].

Historically, Ethiopia has faced multiple seasonal drought events due to erratic rainfall and climate change [22]. The most drought-prone areas in Ethiopia are in Northeast Ethiopia and the Upper Blue Nile basin, including the Northern Tigray region, some parts of Amhara regions, such as South Wollo, North Wollo, South Gondar, and Afar Region, most parts of Somalia Region, and Eastern parts of Oromia Region [1, 3, 23, 24, 25, 26, 27]. Drought in Ethiopia occurs at a recurrence interval of 3–10 years [1], and even though this frequent recurrence is common, there still lacks any firmly established drought mitigation measure for these events. Only short-term response efforts are provided in the form of food aid when food supplies have decreased significantly due to extended drought.

Meteorological drought analysis has been studied frequently, yet hydrological and agricultural drought analysis and monitoring are not studied adequately. It is thought that Ethiopia is a water tower in East Africa but water resource management over the region is not well developed. This aggravates the natural hazard, such as drought impact on human life. Hydrological drought has a great influence on water supply irrigation and power production by reducing the availability of surface and subsurface water. There are few dams and reservoirs in the country and most of them are hydropower plants. But there is a lack of water conservation to reduce drought impact when it occurs. Generally, drought monitoring and forecasting studies are untouched and need a thorough investigation to alleviate socioeconomic problems related to drought.

The objective of this review chapter is to assess the status of hydrological drought studies in Ethiopia by reviewing different previously studied article papers related to drought. A total of 24 article papers was reviewed and the master plan of the eight-river basin was also reviewed. Of these, only two papers were related to hydrological drought and the remains were about meteorological and other drought-related topics. This implies that hydrological drought studies in Ethiopia require further analysis, monitoring, and forecasting investigation. Therefore, it is important to do this kind of review to show the gap of drought studies over the region for future researchers, stakeholders, and planners to develop a suitable early warning system.

2. Materials and methods

2.1 Description of the study area

Ethiopia has an ample amount of water resources when compared to other African countries yet the development is still poor. There are 12 major river basins in the country which generate an annual runoff of 123 BM³ (Table 1). From these, Aysha and Ogaden river basins are dry and the Mereb and Denakle have insignificant streamflow over the year, the border basins from North to East direction (Figure 1). Eight river basins have a well-organized master plan, however, only the three river basins (Abbay, Awash, and Tekeze) are popularly studied for the development of irrigation, water supply, and hydropower projects. Different types of drought studies were also relatively studied in these river basins. In the Wabishebele river basin, one hydrological drought analysis was studied by Awas [26]. Abbay and Awash basins have good hydrometeorological data and are highly invested when compared to other river basins. This review is focused on the assessment of hydrological drought analysis and the drought mitigation approach of previous research in Ethiopia, related to drought.

River basin	Area (km^2)	Annual runoff (BM^3)	Terminus
Abbay	199,912	52.6	Mediterranean
Awash	110,000	4.6	Within the country
Baro	75,912	23.6	Mediterranean
Genale Dawa	172,259	5.8	Indian Ocean
Omo Gibe	79,000	17.9	Lake Turkana
Tekeze	82,350	7.6	Mediterranean
Rift Valley	52,000	5.6	Chew Bahir
Wabishebele	202,220	4.6	Indian Ocean
Mereb	5900	0.26	Sudanese Wetland
Denakle	64,380	0.86	Within the country
Aysha	2223	0
Ogaden	77,120	0
Total	1,123,276	123.42

Table 1.

Characteristics of Ethiopian major river basins.

Source: River Basin Master Plan; Ministry of Water, Irrigation and Electricity, Ethiopia.

Figure 1.

Drought study information of Ethiopian river basins.

Figure 2.

Seasonal variation of streamflow over Ethiopian river basins.

Spatially, the Abbay river basin is the largest and it covers 43.1% of the surface runoff of the country. The general characteristics of each river basin in the country are given in Table 1. In Ethiopia, there is a high seasonal flow and rainfall variation. As shown in Figures 2 and 3, Abbay and Omo gibe river basins have a high flow when compare to other river basins and overall the maximum flow is obtained during the summer season from June to August (JJA).

Ethiopia has 12 major river basins, most of which are transboundary rivers except the Awash river. The total surface water is estimated at 124 BM³ and the groundwater potential is estimated near 30 BM³ [28]. Up to 70% of the surface water is originated from the central and western highlands on the western sides of the Great Rift Valley flow to the west into the Nile river basin system that covers 39% of the landmass and the remaining 30% of surface water originated from eastern highlands flow into east that covers 61% of the landmass.

Figure 3.

Mean monthly rainfall of eight river basins in Ethiopia.

2.2 Historical drought in Ethiopia

Ethiopia is experienced severe drought problems for the last decades. According to Mohammed et al., the most drought years in North East Highlands of Ethiopia were 1984, 1987, 1988, 1992, 1993, 1999, 2003, 2004, 2007, and 2008 [1]. Bayissa et al. also found that 1984/85 and 2003/04 were the extreme drought years in the Upper Blue Nile basin in Ethiopia [29]. Based on EM-DAT, 2014, the most severe drought years in Ethiopia from 1900 to 2013 were 1965, 1969, 1973, 1983, 1987, 1989, 1997, 1998, 1999, 2003, 2005, 2008, 2009, and 2012 with an average recurrence interval of 4 years [30]. Generally, the year 1984 was a bad drought event in Ethiopia and it was globally known. Here, all the above-stated drought years were analyzed based on meteorological drought indicators, especially standardized precipitation index (SPI) and palm drought severity index (PDSI).

2.3 Data collection and analysis

To review the status of hydrological drought conditions in Ethiopia, important data were collected from the Ministry of Water, Irrigation, and Electricity, department of Basin Development Authority. The river basin master plan was thoroughly reviewed and previous drought-related studies in Ethiopia were also assessed.

During this review, 24 articles and conference papers related to drought studies in Ethiopia were collected. From these, nine papers are meteorological drought studies, seven papers are general drought impact studies, and the remaining eight were agricultural, hydrological, and socioeconomic drought studies (Tables 2 and 3). Surprisingly, except for some general drought studies related to drought impact over the country, other drought studies were conducted in some specific parts of the country. Especially meteorological drought studies were highly focused on the Abbay river basin (Upper Blue Nile) and Awash river basin. Agricultural and socioeconomic drought studies slightly tried to see the overall drought conditions in Ethiopia. However, these are also not studied in-depth.

No.	Author	Title	Drought Category
1	Philip et al. [22]	Attribution analysis of the Ethiopian drought of 2015	General
2	Belayneh et al. [2]	Long-term SPI drought forecasting in the Awash river basin in Ethiopia using wavelet neural network and wavelet support vector regression models	Meteorological
3	Yimer et al. 2017	Meteorological drought assessment in northeast highlands of Ethiopia	Meteorological
4	Araya and Leo Stroosnijder, 2011	Assessing drought risk and irrigation need in northern Ethiopia	General
5	Enyew et al. [27]	Assessment of the impact of climate change on hydrological drought in Lake Tana catchment, Blue Nile basin, Ethiopia	Hydrological
6	Edosa et al., 2010	Drought analysis in the Awash river basin, Ethiopia	Hydrometeorological
7	USAID Report, 2018	Economics of resilience to drought; Ethiopia analysis	Socioeconomic
8	Philip et al. [22]	The drought in Ethiopia, 2015	General
9	Jjemba et al.	Extreme drought in Ethiopia stretches drought management systems	Socioeconomic
10	Gebrehiwot et al. [24]	Spatial and temporal assessment of drought in the Northern highlands of Ethiopia	Meteorological
11	Bayissa et al. [17]	Comparison of the performance of six drought indices in characterizing historical drought for the Upper Blue Nile basin, Ethiopia	Meteorological
12	Awass [26]	Hydrological drought analysis occurrence, severity, risks: the case of Wabishebele river basin, Ethiopia	Hydrological
13	EL Kenawy et al., 2016	Changes in the frequency and severity of meteorological drought over Ethiopia from 1960 to 2013	Meteorological
14	Bayissa et al. [29]	Spatio-temporal assessment of meteorological drought under the influence of varying record length: the case of Upper Blue Nile basin, Ethiopia	Meteorological
15	Zeleke et al. [18]	Trend and periodicity of drought over Ethiopia	Meteorological
16	Teshome and Zhang [20]	Increase of extreme drought over Ethiopia under climate warming	General
17	Viste et al. [19]	Recent drought and precipitation tendencies in Ethiopia	General
18	Getachew et al., 2020	Application of artificial neural networks in forecasting a standardized precipitation evapotranspiration index for the Upper Blue Nile basin	Meteorological
19	Getachew, 2018	Drought and its impacts in Ethiopia	Socioeconomic
20	Temam et al., 2019	Long-term drought trends in ethiopia with implications for dryland agriculture	Agricultural
21	Dawit et al., 2019	Comparison of meteorological and agriculture-related drought indicators across Ethiopia	Meteorological and agricultural
22	Y.A. Bayissa et al., 2018	Developing a satellite-based combined drought indicator to monitor agricultural drought: a case study for Ethiopia	Agricultural
23	IDA GRANT-H0280, 2011	Emergency drought recovery project (EDRP) in Ethiopia	General
24	Sara Pantuliano and Mike Wekesa, 2008	Improving drought response in pastoral areas of Ethiopia	General

Table 2.

Summary of selected literature related to drought studies in Ethiopia for this review.

N0.	Basin	Article related to meteorological drought	Articles related to hydrological drought
1	Abbay	3	1
2	Awash	2
3	Omo-Gibe	1
4	Rift Valley	1
5	Tekeze	2
6	Wabishebele		1

Table 3.

Different types of drought studies status in each river basin.

Agricultural and socioeconomic drought studies were not focused on a particular river basin. Total 13 articles, including agricultural, socioeconomic, and general concepts, and drought impacts in Ethiopia were covered in some parts of the country without specifying a particular river basin.

3. Result and discussion

3.1 Hydrological drought status of the country

Ethiopia has been affected by drought many times over the last few centuries. However, drought studies and mitigation measurement investigation are still limited. Although there are few drought studies in the country; it is insufficient. Especially agricultural, hydrological and socioeconomic drought studies are untouched. As shown in Table 4 and Figure 4, most drought studies in Ethiopia are focused on meteorological drought and other general drought-related impact assessments. Meteorological drought is highly varying within the short-period scale in a month depending on the precipitation variability. Therefore, drought analysis from a short-time scale may lead to an erroneous conclusion. But hydrological drought study requires a long-term time scale greater than 6-month cumulative drought conditions of the study area. Mostly hydrological drought analysis is conducted annually based on and above, which will give some concrete information about the drought situation of a particular study area. From this review, hydrological drought studies were covered only 8.33%, which implies that it needs further study (one article in Abbay subbasin and one article from Wabishebele basin). Almost 78% of the study were concentrated in North Eastern and Upper Blue Nile basin, Tekeze and Abbay, and Awash river basin and which is meteorological drought (Table 3). Two researchers have been studied, hydrological drought in Abbay and Wabishebele basins (Table 3). But the remaining six basins are still not studied. Now the government of Ethiopia is planning to transform from agricultural lead to industrial transformation. This will have achieved when the natural resource will be properly managed and utilized. Water is the central part of all infrastructures development. However, the master plan of major river basins in Ethiopia focused only on the potential assessment of irrigation and hydropower, and there is no drought trend analysis and future hydrological drought forecasting. Hydrological drought affects irrigation, water supply, hydropower, and other water-related sectors. So, it is important to study the historical hydrological drought characteristics, such as frequency, magnitude, duration, severity, and future probability of the basin streamflow to satisfy all demands.

Type of drought	Number of studies	Percentage (%)
Meteorological drought	9	37.5
Hydrological drought	2	8.33
Agricultural drought	3	12.5
Socioeconomic drought	3	12.5
General related to drought impact	7	29.16
Total articles reviewed	24	100

Table 4.

Types of drought studies over Ethiopia.

Figure 4.

Percentage of drought studies in Ethiopia (MD = meteorological drought, HD = hydrological drought, AD = agricultural drought, SED = socioeconomical drought, and GD = general drought-related studies).

As far as reviewed from the basins master plan report and previous pieces of literature, there is no method adopted to analyze the hydrological drought in the region. But for sustainable water resource development, mitigation measurements of the extreme hydrological events, such as floods and drought, are impropriated. Otherwise, simply constructing any structure in the basin alone may not be a solution to improve poverty over the country.

3.2 Meteorological and agricultural drought

From the reviewed papers, 37.5% was covered meteorological drought analysis and monitoring studies, and agricultural drought studies were covered 12.5% (Table 4). Ethiopia is highly dependent on rainfed agriculture; so, meteorological and agricultural drought analysis, monitoring, and early warning system development are crucial. But still, there is no well-adopted drought analysis technique for a nationwide or a regional level. As a result, the development of drought early warning system has lacked. At the same time, hydrological drought analysis and monitoring is also key point for river basin development and water resource management. But due to its large input data requirement, hydrological drought study is not further investigated.

3.3 General drought-related studies

The socioeconomic of Ethiopia is continuously affected by frequent drought disasters. It is difficult to cope with subsequent years after drought has occurred. Up to 29.16% of the reviewed papers were related to drought impact, attribution, economics resilience to drought, extreme drought assessment, trend, and periodicity of drought in Ethiopia [4, 18, 19, 20]. Except for some articles, most of the reviewed articles were conducted in some parts of the country and did not give good information about the effect of drought in the country.

4. Conclusion

During any river basin master planning, considering extreme hydrological events, such as floods and drought, are the important issues for sustainable water resource development. Otherwise, simply focusing on the investigation and assessment of the available natural resources in a specific river basin and utilization of the resource will never bring development. Particular attention is to be given to drought-affected areas and conjunctive use of ground and surface water is encouraged. Aridity is the general characteristic of an arid climate and represents a (relatively) permanent condition, while drought is temporary. In an arid climate, drought can still occur when local conditions are even drier than normal. But 90% of the reviewed studies in Ethiopia were conducted on arid and semiarid areas of the region. Generally, hydrological drought study lacked in the country. Therefore, in the future, it is important to focus on hydrological drought monitoring and forecasting to achieve the sustainable utilization of available water resources in Ethiopia.

Acknowledgments

All the river basin master plan documents were freely accessed from the Ministry of Water, Irrigation, and Electricity of Ethiopia. Therefore, great gratitude is given to all the staff members of the ministry, especially for Basin Development Authority Department.

Conflict of interest

We declared that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this chapter.