1. The challenge of managing water
resources under uncertainty
Meron Teferi Taye, REACH Ethiopia program manager
Water and Land Resources Center
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2. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Challenges of climate variability
• Awash is a basin of extremes
– Awash is a great example of uneven
distribution of water in space and time.
• Temporal variation
– Wet season (kiremt) brings devastating
floods and dry season causes water
scarcity and droughts.
• Spatial variation
– Upstream areas (highlands) receive on
average 1600 mm rainfall/year while
downstream areas (lowlands) barely get
100 mm rainfall/year
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0
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Jan
Feb
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Apr
May
Jun
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Aug
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Temperature(°C)
Monthlyrainfall(mm)
Rainfall Temeprature
Kiremt
Belg

3. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Water availability per capita
• Water availability per capita of
Ethiopia is reaching the absolute
water scarcity threshold, 1000
m3/capita/year
– But in Awash basin it is already under this
threshold at 325 m3per person/year
(Adeba et al. 2016).
• Annual variability of rainfall in the
Awash basin
– The last decade experienced below
average years mostly.
-40%
-30%
-20%
-10%
0%
10%
20%
30%
40%
1982
1984
1986
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2016
Precipitationanomaly(%)
Year
Awash
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8000
1950 1970 1990 2010
Populationnumber(inmillion)
Water/capita/year(m3)
Year
Water per capita Threshold Population

4. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
• For the graph in previous slide we can have decreasing trend only if we
start after 1984, still it won’t be significant
• But the years after 2007 there are more drier years
• Couldn’t find data on awash population as timeseries, anyone?
To be deleted
y = -0.0021x + 0.0346
R² = 0.0277
-40%
-30%
-20%
-10%
0%
10%
20%
30%
1985
1986
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5. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Climate change threat
• Long term planning in the basin is also threatened by climate change
– Temperature is increasing under all climate scenarios
– The area covering the Awash basin shows mean temperature increment of 1.5°C to 3°C in
the coming decades until 2100
• This will have implications on precipitation and water resouces
Source: KNMI climate explorer, 2019

6. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Climate change impact uncertainty
• Estimating the impact of climate
change impact on water resources
requires several steps.
– Climate models, downscaling methods,
hydrological models
• At all these steps there are sources
of uncertainty that influence the
climate change impact estimates on
water resources

7. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
• Challenge of data availability and
reliability is one of them
– Stream gauges are scant as we go
down to the downstream of the basin
– Not so much information is available
on water abstraction
• Using methods/tools that deal
with low data availability is
important in climate change
impact estimations to reduce
uncertainty sources
Climate change impact uncertainty

8. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Climate models evaluation
• One source of uncertainty
comes from the climate models.
• Analysis was done to find out
ability of models at reproducing
the historical climate.
– Four metrics were used including:
Seasonal cycle, Trends, Mean bias,
and Variability
• Three climate models met the
selection criteria
– This were used to find out the
projections for hydrological
variables

9. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Impact on hydrological variables
• Temperature projections
– Consistent increasing trend until the
end of the century
• Precipitation projections show
different signs for different
months.
– April is drier than the rest of the
months with precipitation decrease
of 24% on average.
– May is projected to be drier by 14%
on average.
– June to August projected on
average increase in precipitation of
4%, 9%, and 6%, respectively.
Mid future (2031–2055) precipitation projections

10. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Impact on hydrological variables
• Changes were evaluated at scale of
multidecadal mean water availability
averaged over the basin area
– 𝑊𝐴 𝑚 = 𝑃𝑚 − 𝐸𝑇 𝑚
– 𝑊𝐴_𝐶𝐹𝑚 = 𝑊𝐴_𝑓𝑢𝑡 𝑚 − 𝑊𝐴_ℎ𝑖𝑠 𝑚
– Note that this is not streamflow at outlet
of the basin
• This estimate or tool shows projected
climate signal over the basin for long
term planning
– Ignores the complexity related to
population dynamics, abstraction, etc.
– It’s singles out impacts only due to climate
change

11. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
Impact on hydrological variables
• April to June are projected to face
more intense water stress than the
rest of the months
– Due to decreasing precipitation and
increasing temperature
• April to June are critical for irrigators
– Data from Awash basin authority on crop
water requirement for 23 farms in the
basin demonstrate highest requirement in
May
• This water stress is a potential conflict
source among irrigators
– Also between sectors such as hydropower
and irrigation
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Meancropwater
requirement(m3)
Millions

12. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
• Additional climate risk metrics
are being mapped to look at
seasonal scales with prolonged
extreme events or consecutive
dry seasons are being mapped
by:
– Counting the number of times there
are seasons that are lower than a
given threshold consecutively
representing consecutive dry
seasons
– In the figures, 1 Standard deviation
below average rainfall is set as a
threshold for 1981-2017 period for
selected consecutive seasons
– Consecutive dry Belg- Kiremt
seasons are more common in the
eastern part of the basin
Additional climate risk metrics
Belg-Belg
Kiremt-Kiremt
Belg-Kiremt
How much stronger or probable such events will be can be
estimated from climate models projection (ongoing work)

13. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
• The basin has both climatic risks and decision making risks
– Short term, long term, temporal and spatial variability
• The climate signal tool provide information for longer term planning
• Dry season water shortage/stress is projected to increase in the future
as a result of climate change in the Awash basin
– Note that uncertainty in precipitation is still a challenge for our region. But uncertainty
by itself is an outcome that water managers should be aware of and plan towards
strategies that work under a range of scenarios
Planning with uncertainty

14. REACH Water Security and Poverty Conference
27-29 March | Keble College, Oxford
• Sustainable and collaborative water allocation systems, efficient water
use mechanisms need to be in place
– This calls for better coordination of upstream and downstream water managers and
users
• The need to refine our knowledge on the basin’s resource base is still
paramount
– Understanding groundwater helps to set up climate resilient water supply systems
(ongoing work on GW in Awash)
Planning with uncertainty

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