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IJRAR19L1973 International Journal of Research and Analytical Reviews (IJRAR) www.ijrar.org 707

Flooding in Ethiopia; Causes, Impact, and Coping

Mechanism. A Review

Brook Legese * and Boneya Gumi**

*Lecturer and Researcher at Bule Hora University, Department of Natural Resources Management,

Bule Hora, Ethiopia.

**Postgraduate Student at Bule Hora University, Department of Natural Resources Management,

Bule Hora, Ethiopia.

Abstract Flooding is usually thought of as a result of heavy rainfall, snowmelt, land subsidence, rising of groundwater, dam failures.

Coastal flooding, river flooding, flash flooding, urban flooding , and snowmelt flooding are kinds of flooding. Among them, flash

flooding and river flooding occurs often, and negatively impacts human lives and economic asset in Ethiopia. As flood risk and its

impacts are increasing from time to time in Ethiopia, the main objective of this paper is to review flooding and it`s coping

mechanisms in Ethiopia. The factors affecting flooding are the size of the catchments, the intensity of rainfall and amount of

precipitation that fall under the watershed and tributaries, topography, the presence and absence of vegetation, anthropogenic

activity within the catchment areas and catchment area are discussed within this paper. And also, the mechanism of reducing flood

impacts like flood alert and metrological forecasting agency established but the cop ing and mitigation strategies are very low in

Ethiopia. So that, forward suggestions are these strategies need to supplement one another, their coordination must include

“multi-actor, multi-level, and multi-sector involvement and is realized for instance, by collaborative leadership. Stakeholder and

community involvement and a standard knowledge basis also are fundamental. Check dams, terracing, bunds, percolation tanks,

and storage tanks were proposed for various locations across the watershed as effective landscape-based flood risk mitigation

strategies. Moreover, the coping strategies are very needed like insurance, perennial crops farming along with flood-prone areas

and within the river's bank, and the waterway management is more needed to reducing the river flood inundate. This review

recommends new policy approaches that will increase the effectiveness of the present flood coping strategies to sustainably address

the impact of flooding on human health.

Keywords: Floods, Inundate, Heavy Rain, Coping Mechanism

Introduction

Flooding, signifying the consequences of a flood as distinct from the flood itself, is defined as overflowing by the water of the

traditional confines of a stream or other body of water, or accumulation of water by drainage over areas that aren't normally

submerged (WMO,2011). Floods affect more people per annum than all other natural and technological disasters put together. The

damage caused by floods to people and property across the planet has been extremely severe in recent decades (Doswell,2003).

Consistent with Associated Program on Flood Management (APFL, 2008 cited in Niguse and Adhanom, 2019), flood impact tends to

be very severe in African cities where urbanization has taken place with improper land use planning and lac k of early warning

systems. it's the second and therefore the worst environmental disaster next to the recurrent droughts in Africa. most countries in Sub-

Saharan Africa are exposed to at least one or multiple of the natural hazards. Flood usually affects large river basins like the Congo,

Niger, Nile, and Zambezi basins (Niguse and Adhanom, 2019).

Ethiopia has a particularly variable climate, land of droughts, and floodings. Floods are often explained as excess flows exceeding the

transporting capacity of the river channel, lakes, ponds, reservoirs, system, dam, and the other water bodies, whereby water inundates

outside water bodies areas. A flood may be a continuous natural and recurring event in floodplains of rainfall areas like Ethiopia,

where over 80% of annual precipitation falls within the four wet months (June, July, August, and September) (Getahun and

Gebre,2015). The flooding is often caused by, heavy rain, snowmelt, land subsidence, rising of groundwater, dam failures. The natural

disaster associated with weather system variability, global climate change, and environmental degradation is frequently

influencing citizenry and their impacts seem to possess greatly increased in recent decades. Flood is one of the main natural disasters

that are affecting many countries or regions within the world year after year. When water inundates normally dry land, this is

often called a flood. Floods are often caused by a variety of processes, but the dominant cause in Ethiopia is rainfall (Getahun et al,

2016). Flood is a natural action, but mankind`s activities accelerate flooding. It occurs at irregular intervals and varies in size area of

extent and duration. Floods produce damage through the immense power of moving water and thru the deposition of dirt and debris

when floodwaters finally recede (Doswell,2003).

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When rain falls over a neighborhood of land some are absorbed by the soil, while the resent becomes runoff and flows downhill. The

world of land that contributes runoff to a specific point is named the catchment. Heavy, intense rainfall can occur suddenly, and

quickly rising floods caused within the minutes or hours after the rainfall are referred to as flash floods. It is typically related

to relatively small catchment areas where there could also be little or no permanent flow of water. In larger catchment areas, rainfall

can build up over hours, days, or weeks. The runoff from this rainfall flows across land then down gutters, drains, gullies, creeks, and

rivers may create significant floods that inundate large areas of land for days, weeks , or months. Floods are many

various types, like coastal flooding, river flooding, flash flooding, groundwater flooding, and drain and sewer flooding. Among them,

flash flooding and river flooding occurs and negative impacts human lives and economic asset in Ethiopia (Tolera, 2019).

So, this paper focused on Flooding and coping mechanisms in Ethiopian.

2. Flooding and It’s Coping Mechanism in Ethiopia

2.1. Concept and overview of a general description of Ethiopia

Ethiopia is found within the horn of Africa with a neighborhood of 1, 127, 127 sq. km, of which, 7,444 sq. km is a water body (CIA

World Factbook, 2006). The topography of Ethiopia is very diverse, with elevation starting from -125 m at the Danakil Depression to

4620 m at RasDejen. quite 45% of the country is dominated by a high plateau with a sequence of mountain ranges that are divided by

the East African valley. Ethiopia is both a highland/mountainous (with an elevation greater than 1500 m) and lowland (with

elevation but 1500 m) country. It's composed of some nine major river basins, the drainage systems of which originate from the

centrally situated highlands and make their way right down to the peripheral or outlying lowlands.

The climate in Ethiopia is geographically quite diverse, thanks to its equatorial positioning and varied topography. Three general

temperature zones are apparent–cool, temperate, and hot–categorized predominantly by elevation. The cool zone incorporates parts of

the north-western plateau, at elevations above 2,400 meters; the Temperate Zone lies between 1,500 and 2,400 meters and supports

most of the population. the recent zone, at elevations below 1,500 meters, constitutes much of the eastern and southern portions of the

country, also because of the tropical valleys within the west and north. The annual be due to its rivers amounts to 122 billion

m3(Enyew and Steeneveld,2014).

All of this is often generated within its borders and goes across to other countries. because the topography of the country is

quite rugged with distinctly defined watercourses, large scale flooding is restricted to the lowland flat parts of the country. However,

intense rainfall within the highlands causes flooding of settlements during several river basins. one of these is that the Awash basin is

located within the valley and with an area of about 113,000 km2, which has the most important level of development (Getahun and

Gebre, 2015).

Climate change will alter flooding around the globe, and thus an increasing number of studies are modeling the impact of global

climate change on floods, with the main target generally on changing the magnitude and frequency of the flood events (Booij, 2005;

Gain et al., 2013; Raff et al., 2009). However, future projections of the meteorological tr iggers, including heavy precipitation and

snowmelt, may change differently and alter the characteristics of the flood events (Hall et al., 2014). As a result, factors related to the

causal sort of flood-like seasonality and triggering conditions should be addressed next to the change in frequency or magnitude of

floods (Turkington et al., 2016).

River flooding may be natural events and a part of the hydrological cycle of rainfall, surface and groundwater flow, and storage.

Floods occur whenever the capacity of the natural or man-made system cannot cope up with the quantity of water generated by

rainfall from the basin. With prolonged rain falling over broad areas rivers are fed by a network of ditches, streams, and tr ibutaries

and flow build-up to the purpose where the traditional channel is overwhelmed and water floods onto surrounding areas. On large

rivers, flooding occurs a substantial period after the Rainfall and lasts for an extended time because the large volumes of water drain

out of the catchment (Abdisa,2019). The occurrence of a flood depends on meteorology, topography, land use, soil type, and

antecedent moisture conditions (Youssef, et al. 2016; Agbola, et al. 2012). Proper estimation and management of floods play

significant roles within the design of hydraulic structures and environmental protection. However, in Ethiopia, understanding flood

magnitude estimation and management isn't achieved an advanced stage. due to this, many property and life are damaged in Jimma

town frequently (Abdisa,2019). The study of flood and flood management strategies require s the estimation of the flow of water in

river channels (Chandniha and Kansal, 2017; Bouwer 2013). Flood risk has been historically affecting Dire Dawa city since the

establishment of the town (Sitotaw and Hailu, 2018). albeit, adequate records on urban floods of Dire Dawa city were patchy and

incomplete, historical information revealed that the primary damaging flood risk was recorded in1945. Since then flood has been

affecting the town at different times. Different authors have investigated the causes of arriving Dire Dawa city

concerning geomorphology, hydrology, and land-use changes (Yonas 2015; Girma and Bhole 2015; Alemayehu 2007).

The municipality has also been constructing flood protection around the banks of Dechatu and Goro Rivers to guard the town from

flood induced damages. The upstream area of the Awash basin has been flooded for brief durations after intense or prolonged rainfall

events, but the downstream area has been flooded for weeks or months per annum during the wet season (Getahun and Gebre 2015).

The impact of flood including poverty and high increase let many of us become victims for various disasters. as an example, in

Ethiopia, rainfall attributed to the summer rains has led to extensive flooding. As flood risk and its impacts are increasing from time

to time, the emphasis was given by flood research scholars to know the basic causes of flood risk and its mitigation strategies

(Haile,2018).




2.1 Types of floods

Different types of floods also can have different effects in terms of their impact, damage, and price, both financially and to the people

that experience them. Descriptions and categorizations of floods vary and are supported by a mixture of sources, causes, and

impacts. Supported such combinations, floods are often generally characterized into river (or fluvial) floods, pluvial (or overland)

floods, coastal floods, groundwater floods, or the failure of artificial water systems (Tilahun, 2018). This sort of flood is characterized

by sudden onset with a little time interval for early warning and sometimes leading to considerable damage to lives, livelihoods, and

property (FDRENDRMC,2018).

2.1.1 Flash floods

These floods are frequently related to violent convection storms of a brief duration falling over a little area. Flash flooding can occur

in almost any area where there are steep slopes but is commonest in mountain districts subject to frequent severe thunderstorms. Flash

floods are often the result of heavy rains of short duration. This particular sort of flooding commonly washes away houses, roads, and

bridges over small streams then features a critical impact on communities and transport in these often-remote areas. Flash floods are

defined as those flood events where the increase in water is either during or within a couple of hours of the rainfall that produces the

increase and occur within small catchments, where the reaction time of the catchment area is brief (Doswell,2003).

Many hydrological factors have relevance to the occurrence of a flash flood: terrain gradients, soil type, vegetative cover, human

habitation, antecedent rainfall, then on (Tilahun, 2018). Flash floods are those formed from excess rains falling on upstream

watersheds and gush downstream with massive concentration, speed, and force. Often, they're sudden and appear unnoticed.

Therefore, such floods often end in a substantial toll; and therefore the damage becomes especially pronounced and devastating once

they transit or along with human settlements and infrastructure concentration. The recent incident that the Dire Dawa City

experienced is typical of a flash flood (Bishaw, 2012).

2.1.2 River Floods

River flooding is happening over a good range of river and catchment systems. Floods in river valleys occur totally on flood plains or

wash lands as a result of flow exceeding the capacity of the stream channels and spilling over the natural banks o f artificial

embankments. River floods, in contrast to flash floods, typically unfold over days, or maybe months (Doswell, 2003).

Inundations in river valleys are the foremost widespread and frequent sort of flood, and that they are caused by waves of high waters

running downstream. Various mechanisms are liable for the generation of flood waves, but, despite their different proximate

causes, they will all be attributed to the removal of excess water from a river catchment. The integrated characteristic of a flood

occurring in any river may be a hydrograph; this reflects the change in time of the flow and magnitude of run-off for a given river

cross-section (Figure 1). A hydrograph may be a flood “image”, describing the distribution of flood volume over time. Its specific

features are not equivalent to floods of various origins. Hydrograph volume and shape depend upon the intensity and duration of

rainfall or snowmelt, the dimensions, and shape of the river watershed, and therefore the river network, topography, soil moisture, the

sort of vegetation cover, and land-use. The characteristic features of floods expressed by a hydrograph are maximum discharge, the

duration of the flood rise and recession phases, the entire volume of a flood, and flood asymmetry, expressed as a ratio of flood rise to

a recession. The inundation caused by a flood, its scale, and consequences for nature and humans, depend upon the flood rise rate,

maximum discharge, and duration (Mandych,2005).

Figure1. Basic characteristics of flood wave’s hydrograph (Source: Mandych,2005)




Where; t1 - duration of the flood rising phase, t2 - duration of the recession phase, V - flood volume ( ris rec V = V +V ), ris V - the volume of

rising phase, rec V - the volume of recession phase, max Q - maximum flood’s discharge, υ - coefficient of flood hydrograph asymmetry (t

1/t2).

As a flood wave moves downstream from its area of origin, the channel routing modifies the form of the hydrograph, increasing the

time of flood rise and therefore the total duration, and decreasing its asymmetry. Flood risk is not steady along a river. It increases in

narrow stream channels and reduces along the river reaches where the channel width is bigger. The speed of a flood wave is slowed

by obstacles, constrictions, and dams within the river channel. Prolonged high flow resulting in flood is caused by increased water

input into the watershed system, caused by rain or snowmelt, usually during the wet season (Mandych,2005). At least 4 people have

died in flash floods that struck in the city of Dire Dawa, Ethiopia, 24 April 2020. Several people have been injured. The flo oding

caused widespread damages to homes and infrastructure, although full damage assessments are yet to be completed. Two of the

fatalities occurred when homes collapsed. Flooding struck after heavy rain caused the normally dry Dachata River that runs th rough

the city to overflow. Heavy rain and flooding have been reported in southern parts of the country. Local observers said the Neri River

broke its banks, flooding parts of Jinka in Debub Omo Zone of the Southern Nations, Nationalities, and Peoples Region (SNNPR) in

the southwest of the country. Further east, flooding was also reported along the Shabelle River in Ethiop ia’s Somali Region, with the

towns of Kelafo and Mustahīl in the Gode Zone said to be among the worst affected (http://floodlist.com/africa/ethiopia-flash-floods-

diredawa-april-2020).

2.1.3 Urban floods

Addis Ababa (the capital of Ethiopia and Africa) is a habitat to one-fourth of the urban population and contributes about half the

national Gross domestic product (GDP) growth of the country (Birhanu, et al,2016). Despite the rapid economic process and

urbanization, flooding is that the major development challenge facing the town. Urban flooding is more intensified by dramatic

changes within the impervious area, additionally to heavy rainfall and extreme climatic events (Birhanu et al., 2016). Urban flooding

occurs when intense rainfall within towns and cities creates rapid runoff from paved and built -up areas, exceeding the capacity of

storm drainage systems. In low-lying areas within cities, the formation of ponds from runoff occurs not only thanks to high rainfall

rates but also due to drainage obstructions caused by debris blocking drainage culverts and outlets, actually because of lack of

maintenance (Birhanu et.al, 2016).

In Ethiopia, urban flood incidents are getting a significant problem in recent years. They are mainly related to poorly designed

urban systems and land use planning. Combined thereto, lack of early warning system and arranged flood disaster mitigation measures

at the national and native level further increases the gravity of the matter (Niguse and Adhanon, 2018). Urban floods are more costly

and difficult to manage (Daniel,2007). We will nonetheless examine the functional differences between urban and rural flooding.

While rural flooding may affect much larger areas of land and hit the poorest section of the population, the impacts of urban floods

are characteristic therein the concentration of population within the urban environment is typically much higher. Therefore, the

damage is more intense and typically more costly. Construction of roads and buildings also acts to extend runoff and results in an

increased likelihood of localized urban flooding (Doswell,2003). The solutions to urban flood risk issues also will be got to be

tailored to the character of the urban built environment. They are going to be hampered by the concentrated nature and density and

therefore the relatively high cost of land within urban environments (Alemayew,2007).

The urban environment is additionally more dynamic requiring consideration of the distribution of population at various

timescales. thanks to rapid urbanization and population increase, low-income communities are forced to settle in flood-prone areas

additionally the poor drainage systems of the town also intensify the danger of flooding. The reduction of green structures and

therefore the increase within the impervious area in urban areas generates more surface runoff even from regular storms and the

situations are going to be worst when poor people settle in areas that are susceptible to flooding like riverine and low-lying

floodplains (Birhanu et al,2016).

2.1.4 Coastal Floods

Areas along the coast could also be flooded thanks to tsunamis, hurricanes, or/and unusually high tides. Also, long-term phenomena

like subsidence and sea-level rise can cause the gradual encroachment of the ocean. Storm surges and high winds coinciding with high

tides are the foremost frequent explanation for this sort of flooding. The surge itself is that the results of the raising of sea

levels thanks to low air pressure . especially configurations, like major estuaries or confined sea areas, the piling from water is

amplified by a mixture of the shallowing of the seabed and retarding of return flow (WOM,2011).

2.1.5 Snowmelt floods

In upland and high-latitude areas where extensive snow accumulates over winter, the spring thaw produces meltwater runoff. If

temperature rises are rapid, the speed of melting may produce floods, which can reach lower parts of river systems. The severity of

meltwater floods will increase if the thaw is amid heavy rainfall and may be further exacerbated if the subsoil remains frozen.

Although a seasonal occurrence where major snowfields exist in headwaters, which can produce beneficial flooding in downstream

areas, severe effects can occur on smaller scales, especially in areas subject to changes between cold and warmer rainy winte r weather

(WOM,2011).


http://floodlist.com/africa/ethiopia-flash-floods-diredawa-april-2020

http://floodlist.com/africa/ethiopia-flash-floods-diredawa-april-2020



2.2 Floods classification

Flood type classification is an optimal tool to cluster floods with similar meteorological triggering conditions. Under global climate

change, these flood types may change differently also as new flood types develop. A weather generator is including a conceptual

rainfall-runoff model to make long synthetic records of discharge to efficiently build a listing with a high number of flood events.

Significant discharge days are classified into causal types using k-means clustering of temperature and precipitation indicators

capturing differences in rainfall amount, antecedent rainfall , and snow-cover and day of the year. The developed methodology has the

potential to be used flood impact assessment and disaster risk management as future changes flooding types will have implications for

both the local social and ecological systems within the future (Turkington et.al, 2016).

As a result, factors related to the causal sort of flood-like seasonality and triggering conditions should be addressed next to the change

in frequency or magnitude of floods. Classifying flood events into differing types can place flooding into a wider climate context and

help with exploring changes in future flood events (Turkington et.al, 2016). The dimensions of a flood event, or its magnitude, are

often expressed in some ways. the height level of the water at a specific location during a waterway is that the most unambiguous

way because it is comparatively easy to live and is that the principal driver of flood impact.

The flood magnitudes are usually classified by their height:

Major: This causes inundation of huge areas, isolating towns, and cities. Major disruptions occur to road and rail links. Evacuation of

the many houses and business premises could also be required. In rural areas, widespread flooding of farmland is probably going.

Moderate: This causes the inundation of low-lying areas requiring the removal of stock and/or the evacuation of some houses. Main

traffic bridges could also be closed by floodwaters.

Minor: This causes inconvenience like the closing of minor roads and therefore the submergence of low-level bridges and makes the

removal of pumps located adjacent to the river necessary.

2.3 Floods Prone Areas of Ethiopia

In flood-prone areas, understanding flood causing factors can increase the knowledge, awareness, and individual initiatives to

guard themselves and their properties using appropriate flood management measures before and through flood events (Haile and

Worku, 2018). Much of the flood disasters in Ethiopia are attributed to rivers that overflow or burst their banks and inundate

downstream plane lands. The flood that has recently assaulted Southern Omo Zone and East Shewa Zone (mainly Dugeda Bora

Woreda) may be a typical manifestation of river floods. Therefore, due to its topographic and altitudinal characteristics, flooding, as

a phenomenon, is not new for Ethiopia. They have been occurring at different places and times with varying magnitude. Some parts of

the country do face major flooding. Most prominent ones include extensive plain fields surrounding Lake Zeway and Meki in Oro mia

Regional State; areas in Oromia and the Afar Regional States that constitute the mid and downstream plains of the Awash River;

places in Somali Regional State that fall mainly along with downstream of the Wabishebelle, Genalle and Dawa Rivers; low-lying

areas falling along Baro and Akobo Rivers in Gambella Regional State; downstream areas of Omo River within the Southern Nations,

Nationalities and Peoples Regional State (DPPA, 2006).

Flooding in Ethiopia is especially linked with torrential rainfall and therefore the topography of the highland mountains and lowland

plains with natural drainage systems formed by the principal river basins. In most cases, floods occur within the country as a result

of prolonged heavy rainfall causing rivers to overflow and inundate areas along the river banks in l owland plains. Among the

main river, flood-prone areas are parts of Oromia and Afar regions lying along the upper, middle , and down-stream plains of the

Awash River; parts of the Somali region along the Wabe Shebelle, Genale, and Dawa Rivers; low-lying areas of Gambella along the

Baro, Gilo, Alwero and Akobo Rivers; down-stream areas along the Omo and Bilate Rivers in SNNPR and therefore, therefore,

the extensive floodplains surrounding Lake Tana and the banks of Gumera, Rib and Megech Rivers in Amhara (see Map 1

below)(FDRENDRMC,2018).




Figure 2. Flood prone areas of Ethiopia

Source: (DRMFSS, 2013 as cited in FDRENDRMC,2018)

2.4 Causes Flooding in Ethiopia

The excess flows in water bodies can happen due to several causes/factors, but seasonal heavy rainfall is that the main explanation

for flooding within Ethiopia`s Rivers Basin. The matter of river flooding thanks to excess rainfall briefly time and therefore

the following high river discharge may be a great concern within the Awash basin, Ethiopia. Within the main season (June, July,

August, and September); the floodplain of the Awash River extends to particular areas that are not normally covered with water. The

river or flash flooding usually occurs within the low-lying flat topographic areas of the Awash basin. The extreme rainfall within

the highlands of the Awash basin causes flooding at its downstream and damages settlements on the brink of any section of the river.

In most cases, floods occur in Ethiopia as a result of prolonged heavy rainfall causing rivers to overflow and inundate areas along the

river banks in lowland plains. (Getahun and Gebre,2015).These sorts of floods build up slowly and therefore the magnitude depends

on many factors like the size of the catchments, the intensity of rainfall and amount of precipitation that fall under the watershed and

tributaries, topography, the presence and absence of vegetation, anthropogenic activity within the catchments area, catchment area.

Ten factors as elevation, slope, distance from the network, land use, density of the drainage, flow accumulation, surface roughness,

stream power index, topographic wetness index, and curvature of the topography were digitized then contributed within the mapping

of Flash flood. (Hamid et al, 2019).

2.4.1 Natural Causes

Rainfall is the most vital think about creating a flood, but there are many other contributing factors. When rain falls on a

catchment, the quantity of rainwater that reaches the waterways depends on the characteristics of the catchment, particularly its size,

shape, and land use. Some rainfall is ‘captured’ by soil and vegetation, and therefore the remainder enters waterways as flow. River

characteristics like size and shape, the vegetation in and around the river, and therefore the presence of structures in and adjacent to

the waterway all affect the extent of water within the waterway (Garrett, 2011).

The flood may be a consequence of the migration of the boundary between land and water bodies, reflecting the traditional interaction

of the atmosphere, hydrosphere, and lithosphere. Two major factors are liable for flood generation and impart specific

features thereto. The primary is that the physical process, which generates the change of position between the li thosphere,

atmosphere, and hydrosphere. Secondly, the flooded area, depth of inundation, and its duration depend upon the geographic

situation within the region where the flood takes place. Thanks to the good variety operational of the natural processes and therefore

the endless variation within the condition of the geographic arena where they act, many various kinds and scales of floods are

often distinguished (Mandych,2005).

Regional specificity, including climate, determine the foremost characteristic features of floods and their recurrence. The role of the

geographic situation is giving rise to floods is extremely important. as an example, heavy rains are often the explanation

for inundation in river valleys, but they never create floods on sea coasts. within the same way, storms generate surges on low-lying

shores of seas and lakes but never create surges on shores with elevated and steep coasts (Raff,2009).Large amounts of

precipitation could also be typical of a specific season and, accordingly, there could also be a high probability or maybe inevitability

of floods at that point. This is often why floods and their negative effects on populations and economies are most pronounced within

the period up to at least one year (Sitotaw and Hailu, 2018).




When the waters of a flood arise directly from precipitation, atmospheric processes are often identified as directly liable for the event.

That is, rainfalls occur that are well beyond the typical values for the affected area. it's only those rainfalls exceed the type that

typically dry land is often affected; that's, a flood occurs. Thus, the rainfall amounts needed for floods cannot be defined in absolute

terms (Doswell,2003). These hydrological factors determine the response of the catchment to the precipitation event. Thus, a flash

flood is the result of the concatenation of both meteorological and hydrological circumstances.

2.4.2 Anthropogenic Causes

A flood may be a natural disaster. However human activities in many circumstances change flood behavior. Activities within

the catchment like land clearing for agriculture may increase the magnitude of a flood which increases the damage to the properties

and life. Intensive agricultural activities on steep slope areas of the catchment and its expansion decrease the abstraction of rainwater

and thereby changed quickly to flood water (Bishaw, 2012). Large scale floods that originate from, and are exacerbated by, an act is

often put into a selected group. Deforestation of forests, drainage of wetlands, and urbanization are the main causes of rapid

increase within the flow of rivers, giving rise to floods. Reservoir construction, additionally to changing river flow regime also

can trigger a variety of other negative consequences that promote flooding (Gumma et al,2020 and Amdemariam et al,2020).

Impermeable urban areas increase the flood hazard problem. High levels of urbanization in river flood plains and different parts of its

catchment may additionally change the frequency of occurrence of flooding during a particular area. Due to the complications related

to impermeable surfaces, drainage systems, solid waste, debris, movable assets , and therefore the sites of buildings, the predictability

of flood flows were much lower once the affected urban settlement was reached (Daniel, 2007).

Problems arise when increases in rainfall and water level rise exceed the traditional carrying capacity of rivers and overwhelm sea

defenses and natural buffer zones. Changes within the use of land can contribute to the increased hazard from flooding by

reducing the pliability of the system to soak up excess water. Land-use change in any part of a catchment may contribute to increases

in urban flooding downstream (Chandniha and Kansal, 2017).

In developing countries, the removal of primary natural canopy forests reduces the power to naturally dissipate rainfall energy and

promote the retention of water. Deforestation especially can contribute to a discount on land cover, and with increasing precipitation,

there is often a rise in sediments in rivers. The removal of ground vegetation for farming further increases the danger of

accelerating the speed of rainfall-runoff and causing erosion. The sudden influx of individuals into upper catchments, often related

to the extraction of minerals, can cause serious land degradation and increase the speed of rainfall -runoff (Enyew and Steeneveld,

2014).

In addition to the risks to lives and property that folks take by getting into flood-prone areas, development for human use often

involves clearing the land of its native vegetation and altering the characteristics of the bottom cover. Vegetation works alongside the

soil to store rainfall, so when that vegetation is cleared, rainfall -runoff can increase substantially. Instead of being absorbed by the

soil and its natural vegetation, in areas where that vegetation has been cleared (either for construction or for agriculture) , heavy

rainfall is more likely to escape and pour into streams and rivers, increasing the potential threat from flash floods and river floods.

Construction of roads and buildings also acts to extend runoff and results in an increased likelihood of localized urban flooding. Such

construction dramatically increases the fraction of the rainfall that runs off, no matter antecedent rainfall. Human-caused fires also

can produce a minimum of temporary increases within the runoff potential within the headwater regions of streams and

rivers. Human activities are increasing the potential for floods around the world (Doswell,2003).

2.5 Consequences of Flooding in Ethiopia

Floods impact on both individuals and communities, and have social, economic, and environmental consequences. The results of

floods, both negative and positive, vary greatly counting on the situation and extent of flooding, and therefore the vulnerability and

value of the natural and constructed environments they affect (Garrett, 2011). Excess water in itself is not a drag. Rather, the impacts

of flooding are felt when this water interacts with natural and human-made environments during a negative sense, causing damage,

death, and disruption. The experience of flooding for a rural agriculturalist and an urban slum dweller is going to be very different:

while to the farmer the flood may be a natural force to be perhaps harnessed or endured for the future benefits, it is going to bring,

whereas, for the urban dweller flooding is at the best a nuisance and at the worst a disaster which destroys everything she or he

owns(Wakuma, 2009).

The effects of a flood on the inundated land and therefore the property located there will differ, counting on local factors and

conditions, and where the flood originates. The most effects are from an accumulation of water and therefore the dynamic impact of

flowing water during the movement of a flood wave. In specific conditions, the consequences of a flood depend upon an

outsized number of additional circumstances, like depth and duration of inundation, the velocity of the flood’s wave movement along

with the river, height and velocity wave travel, then forth (Doswell, 2003).

The impact of flooding is driven by a mixture of natural and human-made factors. Proper estimation and management of floods play

significant roles within the design of hydraulic structures and environmental protection. However, in Ethiopia, understanding flood

magnitude estimation and management is not achieved an advanced stage. Due to this, many property and life are damaged in Jimma

town frequently (Abdissa and Gudu, 2019). The dry lowlands of Ethiopia are seasonally suffering from long periods of low rainfall

and, coinciding with rainfall within the Amhara highlands, floodwaters which flow onto the lowlands leading to damage to landscapes

and settlements (Gumma et al, 2020 and Amdemariam et al,2020).




Different parts of the country are threatened by the quite unprecedented and abnormal magnitude of flooding. for instance, in

2006, quite 357,000 people were suffering from flooding (out of which 600 died, 200,000 became home-less) and therefore

the country lost about 40 million Ethiopian Birr (UNOCHA, 2006). The matter is more acute within the river basins and

concrete areas. For instance, in 2006, flooding in South Omo and Dire Dawa has killed 300 people in Dire Dawa city. Consequently,

many also are affected before the particular information is submitted to the acceptable decision-makers (Daniel, 2007).

Heavy rains across the country have seen further flooding in South Omo Valley, Dire Dawa, Amhara, Afar, Somali, Tigray,

Gambella, and Oromia regions. consistent with government and United Nations (UN) figures, approximately 35,000

people are displaced, 120,000 affected and 620 confirmed dead. These figures do not take under consideration population groups who

have temporarily relocated to higher grounds. The DPPA has issued fresh flood alerts in southern, northern, and western Ethiopia as

more bodies were recovered within the south, where the Omo River burst its banks on 13 August (DPPA, 2006). Thousands of

individuals living within the flooded areas have little shelter or food and are exposed to terrible weather, with the danger of

contracting diseases. The floods have also killed livestock and destroyed large areas of farmland. Flooding has been remaining one

among the severe natural catastrophic within the country, only a few studies are conducted, for instance, Dire Dawa city, Oromia

Region in Dugeda Bora Woreda; Addis Ababa City; Gambella, Amhara Region in Fogera Woreda et al. (Daniel, 2007; Woubet and

Degnachew, 2011; Wakuma et al., 2011; Kebede, 2012).

The upstream area of the Awash basin has been flooded for brief durations after intense or prolonged rainfall events, but the

downstream area has been flooded for weeks or months every year during the wet season. The timing and size of the flood will

influence the assembly of the crops cultivated within the floodplain. many rainfalls at the beginning of the season within the Upper

Awash basin will cause the country to flood, and to deposit fertile sediment within the floodplain. If the extreme rainfall within

the Upper Awash basin will occur at the top of the season, the floods can damage the crops. The floods are getting highly

unpredictable in some ways. Flooding is becoming an enormous concern within the Awash basin thanks to crop damage and human

welfare losses (Getahun, and Gebre 2015). The country experiences two sorts of floods: flash floods and river floods. In Ethiopia,

Flood hazard remains not well-understood due to a limited number of hydrological and stream gauging stations. In Ethiopia, river

flooding hazard usually affects locations on the brink of river banks of cities and towns (Tilahun, 2018).

The 2018 Belg season flood risk areas list was developed supported the NMA 2018 Belg mid-season weather outlook, historical data,

and Regional DPPB flood impact and flood risk areas report, and therefore the regional Emergency Preparedness and Response

plan. Supported the NMA 2018 Belg mid-season and 3rd decade of April weather forecast, better rainfall activity is anticipated to

favor both belg growing areas of the country. Generally, the mid-season rain predicted for much of the country for two months (April

& May) is going to be closest to normal with an opportunity of above-normal rainfall anomalies at some places (FDRENDRMC,

2018).

Source: National flood alert report, April 2018

Figure3. Flood incident in Hargelle woreda (Afder zone), April 2018




Floods can cause a good range of health impacts. The main health impact resulting from flooding are injuries, diarrheal diseases,

vector-borne diseases, malnutrition, psychological state problems, and damage to health infrastructure. Deaths due to flooding can

occur in several ways and periods. But the foremost easily recognized ones are deaths caused by drowning and injuries during the

onset of flooding (WHO, 2002). This doesn't mean that flood deaths are only from drowning and injuries. Flood death also

can occur due to other health impacts of flooding like from communicable diseases (Schwartz et al, 2006). Flood deaths arising from

infectious diseases are higher in developing countries due to poor sanitation, water system, and poor surveillance and detection (Ohl

et al, 2000).

Injuries can occur before, during, and after flooding. It can occur before flooding when people are trying to flee the approaching

water. People also injured during the onset of floods mainly they are hit by an object in fast-flowing water and injuries can occur after

the flood receded when people returned to their homes and business areas and begin to wash up the damages (Ahern et al,

2006). There is little information available on injuries caused by flooding in Ethiopia. Malnutrition is additionally another health

impact of flooding. Floods damage crops and inundate farmland which may cause food shortages. Floods also damage property and

cause displacement of huge numbers of individuals (Ohl et al, 2000). As an example, the 2006 arrive Gambella region resulted in,

1650 ha of maize crop damaged. There was also a 20% reduction in production mainly from flood recession farming as a result

of waterlogging on the farmlands (GRDPPA, 2007). Most of the people suffering from this flood were very poor and thought

of highly vulnerable in terms of food security(Wakuma, 2008).

2.6 Floods Risk Reduction Mechanisms in Ethiopia

2.6.1 Forecasting system

Weather forecasts can provide warning of a flood, and seasonal forecasts can alert of a heightened chance of flooding within

the coming months. However, forecasting river levels and flood extent may be a complex process that is continually being improved

(Mandych,2005). Flood forecasting may be a necessary a part of flood management, as long as no preventative or defense

measures are often completely effective. The truth of economic limits to the supply of defenses, alongside the likelihood that the

capacity of defense systems could also be exceeded or that they will fail, require that other measures are in situ (WOM, 2011).

2.6.2 Early warning system

Flood warning systems turn forecasts into messages designed to scale back the negative impacts of floods. Warning systems should be

accurate, timely, and reliable. Before community awareness of flood risk can make warnings simpler. Improving our warning systems

could reduce social losses from floods (Garrett,2011). Flood warnings are distinct from forecasts, as they are issued when an

occasion is happening or is imminent. Flood warnings must be issued to a variety of users, for various purposes.

These purposes include:

To bring operational teams and emergency personnel to a state of readiness;

To warn the general public of the timing and size of the event;

To warn on the likely impacts on, for instance, roads, dwellings, and flood defense structures;

To offer individuals and organizations time to require preparatory action;

In extreme cases, to offer a warning to organize for evacuation and emergency procedures.

Early warning of a flood may save lives, livestock, and property and can invariably contribute to the lessening of the general impact.

Flood warnings got to be understood quickly and clearly, then considerable attention has got to tend to how technical information is

conveyed to non-specialists from organizations, the general public, the media, and in some cases illiterate population groups (WOM,

2011). The protection and mitigation measures for floods vary greatly too. As flood risk and its impacts are increasing from time to

time, the emphasis was given by flood research scholars to know the basic causes of flood risk and its mitigation strategies (Haile and

Worku, 2018).

Watershed management that is heavily reliant on improved farming technologies often ignores the various water resource related

problems that are caused by non-agricultural land uses. Mining and physical infrastructure like roads, for instance, can affect local

hydrology much more than agricultural practices and may cause uncontrolled runoff and sedimentation of rivers. Effective watershed

management identifies the most problem areas or ‘hot spots’ of risk and sets appropriate priorities for mitigative interventions

(Chandniha and Kansal, 2017). Different coping strategies are wont to reduce the impact of floods on human health and property by

taking measures before the flood happens, during the flood event, and within the aftermath of arriving Gambella region, Ethiopia

(Wakuma, 2008). Ethiopia prescribes the assessment of hazardous areas from surface waters through hazard

and risk maps, which need to be implemented on national and native levels of member states to prevent future flood damage.

Therefore, “a balanced combination of measures on the river itself, within the catchment basin, and the flood risk areas” is suggested.

These are as follows:

Prevention, aiming in danger reduction by lowering the exposure of individuals and properties;

Defense, linked to protection by structural measures and therefore the reduced probability of flooding; and mitigation, to

decrease the vulnerability of areas and other people susceptible to risk (Birhanu et al,2016).




3. Conclusion A flood is a natural disaster and causes loss of life and property destruction. In Ethiopia flooding suffering from many causes like

heavy rainfall during four wet months (June, July, August, and September), high elevation topography, and land use system involves

clearing the land of its native vegetation and altering the characteristics of the bottom cover. Vegetation works alongside the soil to

store rainfall, so when that vegetation is cleared, rainfall-runoff can increase substantially. Due to this and other factors, the flash

flood and river flood are caused to the loss of many life, economy, and environmental destruction within the country.

The mechanism of reducing flooding impacts like flood alert and metrological forecasting agency established but the cop and

mitigation strategies very low in Ethiopia. so that activities within the catchment like land clearing for agriculture increased the

magnitude of a flood which increases the damage to the properties and life. In Ethiopia, individual preparation and recovery solutions

including reconstruction and compensation are not mentioned. These strategies need to supplement one another, their coordination

needs to include “multi-actor, multi-level, and multi-sector involvement and is realized for example, by collaborative leadership.

Stakeholder and community involvement, defined roles and responsibilities, and a standard knowledge basis also are fundamental.

Check dams, terracing, bunds, percolation tanks, and storage tanks were proposed for various locations across the country as effective

landscape-based flood risk mitigation strategies. So, it needs all level stakeholders’ commitments to ensure these mitigation

strategies.

The flooding risk increasing year to year in Ethiopia so that the coping strategies are very needed like insurance, perennial crops

farming along flood-prone areas. Within the bank of the river, waterway management is more needed for reducing the river flood

inundate. Three weaknesses that were identified within the current coping strategies for flood-related health impacts in the country

were a scarcity of flood-specific policy, absence of risk assessment, and weak institutional capacity. This review recommends new

policy approaches that will increase the effectiveness of the present flood coping strategies to sustainably address the impact of

flooding on human health.

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