International Consortium on Geo-disaster Reduction
th15 International Symposium on Geo-disaster Reduction

Matsue – Oki Island – Kyoto
25-30 August 2017

Climate change, human impact and hydro-meteorological hazard inDire Dawa district, Ethiopia
1234Paolo Billi *, Yonas Tadesse , Aklilu Amsalu , Rossano Ciampalini
1 International Platform for Dryland Research and Education, University of Tottori, Tottori, 680-0001 Japan
2 Department of Geography, University of Dire Dawa, Dire Dawa, Ethiopia
3 Department of Geography, University of Addis Ababa, Addis Ababa, Ethiopia

Flash floods in Dire Dawa

4 IRD (French Research Institute for Development), Montpellier, France

In 2006, the town of Dire Dawa experienced a typical flash flood that,
following the heavy rain on the upland areas of eastern Harerge highlands,
within a few hours turned the dry bed of the Dechatu River into a swelling anddevastating river that caused several casualties and property damage formillions of Euros. The problem of flash floods in the semi-arid area of Dire
Dawa is not new, but their frequency has significantly increased in the last
decades (Alemu 2009; DDAEPA 2011). This study aims are: 1) to analyse therecent trends of rainfall intensity in the study area to ascertain if the increased
frequency of flash floods can be associated with an increase of daily
precipitation amounts (Fig. 4); 2) to estimate peak discharges for the Dechatu
River in the recent decades and assess the evidence for changing flood
behavior (Fig. 5); 3) to discern the role of climate change compared to that ofto land use change and human impact in general, i.e. a situation that is common
in many dry lands of developing countries.

* Corresponding author e-mail: bli@unife.itBackground
Records of drought in Ethiopia date back to 250 B.C. and since then droughts have been a recurring
phenomenon in different parts of the country at different times. Recent studies have shown that thefrequency of drought has increased over the past few decades, especially in the lowlands. Drought
episodes are commonly followed by food insecurity leading to several casualties and substantial
livestock reduction. Climate change prediction will worsen the already severe land degradation and will
accelerate deforestation, loss of biodiversity and desertification with negative repercussions on foodproduction and supply. During the last decades, in several parts of Ethiopia, such as the Dire Dawa
district, the effects of climate change were paired and exacerbated by deforestation, overgrazing andpoor land management. This led to an impressive increase in the frequency of devastating flash floods
that repeatedly inundated the town of Dire Dawa, causing several fatalities and relevant property
damage. The town of Dire Dawa and its surroundings (Fig. 1) are therefore experiencing a combinationof hydro-meteorological extremes (droughts and floods), the frequency and intensity of which
increased in the last decades, substantially limiting the economic development of the area.

The return time interval for a daily rainfall intensity I24 =100 mm/24h was calculated using the Gumbel method for
18 meteo-stations uniformly distributed across Ethiopia.
The results of this analysis show that for 50% of themeteo stations the probability of a rainfall intensity of 100
mm/24h is less than one in 20 years. In the Dechatu R.,
rainfall intensities of the same order of magnitude of thosethat generated the devastating flood of August 2006 havea high probability to occur given the short return time
ranging from 14 to 21 years calculated for Dire Dawa andthe neighbouring mete-stations.
The interannual variation of daily rainfall intensity showsa marked increasing trend, with a substantial jump in thelast two decades (Fig.4).

Figure 1. The study area of Dire Dawa

Drought assessment methods
The occurrence of droughts in the study area wasinvestigated by the Standard Precipitation Index(SPI) (Fig. 2) and other parameters, such as the Zscore or the aridity index, and a new parameterbased on the number of days of rainfall onset delay
with respect to the traditional seeding time (Rd).
In Ethiopia, farmers follow a millennial tradition ofadaptation to rainfall seasonality and sow theircrops at the end of February (just before thebeginning of the spring small rains) and at the endof June-beginning of July for the summer big,
Fig. 2. SPI time series at 12-month scalemonsoon-type rain crops.
The sooner the rainfall comes the better it is for seed germination. Instead, if the rain comes several
days after the seeds placement, their germination may be at risk or significantly reduced. Moreover, abird of the francolin family, rather common in Ethiopia, is able to find the seeds also under two-three
centimeters of soil. Though farmers use different means to keep these birds away, the longer the time
between sowing and germination the more seeds are eaten by these birds. On the base of suchconsiderations, a new, very simple parameter was developed to take into account the delay of rain
onset with respect to sowing. For each of the study meteo-stations, the number of days to reach arainfall amount of 20 mm after March 1 and July 1 were counted and then summed. Time series
diagrams of rain delay data (Rd) for both the small spring and big summer rains and their sum wereconstructed and the occurrence of peaks was compared with droughts/famine occurrence since 1955
for Dire Dawa and Haramaya and since 1981 for the other meteo-stations, respectively, with theexception of Combolcha for which data was not sufficient (Table 1). From the comparison with thehistorical drought series, cumulative rain delays in excess of 40-50 days (depending on annualprecipitation) can be considered as indicative of drought conditions.

Fig. 4. Inter-annual variation of daily rainfall intensity
in the study area

Devastating flood threshold
High flood threshold

Drought study results% of matches

According to a few authors and international
institutions (Edossa et al. 2010; Degefu &Bewket 2015), in Ethiopia, major droughts haveoccurred in 1957-1958, 1964-1966, 1972-1974,1982-1984, 1987-1988, 1990, 1999, 2000, 20022003, 2006, 2009 and 2011. This sequence iscompared with the peaks of the aridity/droughtparameters considered in this study, i.e. SPI, theUNEP’s (1992) Aridity Index (Ai), the Z-score(Z) and the rain delay (Rd) (Table 1). The
results indicate the best performance is givenby Rd with about 65 % of matches (Fig. 3)(Table 1).

6570

Frequency (%)

6050

Fig. 5. The floods larger than 300 m3s-1 were calculated from flow level data, filed survey of the cross-section and bed
material grain size and by using the Darcy-Weisbach uniform flow equation. Two other very high floods occurred after
2010.

494536403020
100SPIZAiRdFig. 3 Correct predictions by the different
drought indices considered in this study

Table 1 - Results of different indices (see text for explanations) matching drought/famine episodes(■ = matches: ▬ = doesn’t match; md = missing data).

Dire Dawa

SPIZ
Ai
Rd
Haramaya
SPIZ
Ai
Rd
DengegoSPIZ
Ai
Rd
Kulubi
SPIZ
Rd
Combolcha SPIZ
Total match (%)

195758
md■
■■
md■
md■
md
md
md
md
md
md
md
md
md100

196466
md■
■■
md■
md■
mdmdmdmd
md
mdmdmdmd
100

197274
md
■
■
■
md
▬▬
■
md
md
md
md
md
md
md
md
md
67

198284
md
■
■
■
md
■
▬■
md
■
■
■
md
▬
■
md
md
82

198788
■
■
■
■
▬▬
▬
▬
■
■
▬md
■
■
■
■
■
67

1990

1999

2000

▬■
■
▬▬▬
▬
■
■
▬md
▬▬▬▬▬
▬
25

▬▬
■
▬▬▬
▬
▬
▬▬
▬
▬▬
■
▬▬▬
12■
■
■
■
■
▬md■
▬▬▬
■
▬▬md
▬▬50

200203
■
■
■
▬■
▬▬
■
■
■
▬▬▬
■
▬■
■
622006

20092011■▬■▬▬■
mdmd▬mdmd■
■
▬md
▬▬42■
■
md
▬▬▬▬■
▬▬md■
■■■
▬■
57■
▬md■
▬▬md■
■■md■■▬■▬▬
61Total(%)
7575
83
58
25
33082
50
50
25
63
50
44
57
2543

In the study area, land use/cover changed significantly from 1985 to 2006 and a nick point can be identified in the firstyears following the change of Government (DERG) in Ethiopia that formally occurred in 1992. Late land management
plans of the DERG forced the farmers to set up cultivations also on the on steep slopes of the Dechatu headwater and,though soil countermeasures such as terracing and eucalyptus tree plantations were implemented through the food for work
program, the local farmers considered the natural constraints and limitations too hard to cope with and making suchcultivations scarcely remunerative and rewarding. After the fall of the DERG regime in 1991, these cultivations wereabandoned and grown trees were cut and sold for daily consumption. Presently, only little cultivation is taking place due tothe limitations of soil degradation severity. This important land management transformation, consisting substantially incrop and conservation practices abandonment has left the slopes, especially in the river headwaters, devoid of any efficientsoil maintenance and water conservations practices, de facto giving rise to conditions that favour higher than before
overland flow volumes.
The runoff generated by a rainfall of 100 mm in 24 hours was calculated by the curve number method for the land
use/cover referred to 1985 and 2006. According to this method, the change of land use/cover observed in 2006 is
responsible for a runoff increase of about 4.5%.

Conclusions
1) The semiarid area od Dire Dawa, likewise many other parts ofEthiopia, is subjected to recurring droughts. The rain delay
parameter proved to be the best to identify droughts and to be
used as a simple early warning method to inform farmers of thedrought risk and to let local administrators to deploy timelycountermeasures.
2) The increased frequency of devastating floods in the town of
Dire Dawa (Fig. 6) is the result of a combination of factors: theincreased rainfall intensity in 24 hours recorded in the area and amarked land use change that following the fall of the DERG
government resulted in the abandonment of the steeper land andof the old soil and water conservation implementations.
Fig. 6. The 2016 high flood of the Dechatu R. inDire Dawa.

References
Alemu YT (2009) Socio-economic impact of flooding in Dire Dawa, Ethiopia. Unpublished MSc. Thesis, International Center for Water Hazard
and Risk Management, Tsukuba, Japan, 62 pp.
DDAEPA (Dire Dawa Administration Environmental Protection Authority) (2011) Dire Dawa Administration, program of adaptation to climatechange. DDEPA, Dire Dawa, Ethiopia, 121 pp
Degefu M.A., Bewket W.A. 2015 Trends and spatial patterns of drought incidence in the Omo-Ghibe river basin, Ethiopia. Geografiska Annaler:
Series A, Physical Geography, 97(2), 395–414.
Edossa D.C., Babel M.S. & Gupta A.D. 2010 Drought analysis in the Awash River Basin, Ethiopia. Water Resources Management, 24, 1441–1460, DOI 10.1007/s11269-009-9508-0.

Fig. 7. The river bed area is extensively
occupied by the local people, including apermanent open air market. That has increasedremarkably the number of casualties during thepast floods.