Evaluating Potential Impacts of Climate Change on Surface Water Resource Availability of Upper Awash Sub-basin,

Ethiopia rift valley basin.

ByMekonnen Daba

Paper presented at African Dissemination Workshop on Innovative Application of ICTs in Addressing Water - related Impacts of Climate Change, 12th December, 2014 at Makerere University, Kampala

Introduction

Climate changes

In the surface temperature,

Changes in precipitation

evapotranspiration rate

will accelerate the global hydrological cycle(IPCC, 2007)

(IPCC, 2007) findings suggests that developing countries like Ethiopia will be more vulnerable to climate change due to their economic, climatic and geographic settings.Climate changes alter regional hydrologic conditions and results in a variety of impacts on water resource systems. Such hydrologic changes will affect almost every aspect of human well-being. The economy of Ethiopia mainly depends on agriculture, and this in turn largely depends on available water resources.

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Key Sub-basin Problems

Upper Awash sub-basin is normally endowed with land features that are characterized by:

Downstream irrigation , several towns, including the capital city, Addis Ababa, and industrial enterprises in the study area has been expanding from time to time there is an increasing demand for water which leads to competition for water among different sectors .

Because of fast growing population rates, increasing resources and industrial development, water is becoming a very scarce and valuable resource.

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So What are the Innovations/Solutions?

Therefore assessing the impact of climate change on Surface water resource availability,

Taking projections of climatic variables (e.g., precipitation and temperature at a global scale,

Downscaling these global-scale climatic variables to local-scale hydrologic variables, and

Computing hydrological components for water resources variability and to give a clue and increase awareness on the possible future risks of climate change in order to mitigate the impacts climate change on water resources system.

The general objective of this study is to assess the impacts of climate change on Surface water resource availability of upper Awash River basin by using the Regional climate model and Soil and Water Assessment Tool (SWAT) hydrology model.

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Study Area map2

0’ 0 ’ 0 ’ 0 ’

Area 7240km

Found between

38  to 39 5 00 East 7  00  and 10  30 North

The Awash Basin has been traditionally divided into four distinct zones.

These are; Upper Basin, Upper Valley, Middle Valley and Lower Valley. 

The Methodology used

To evaluate climate change impacts on the water availability of the following steps:•Precipitation, and temperature, is extracted From GCM.•A Dynamic downscale GCM output to RCM•Bias corrected RCM with historical met data. •Meteorological data + observed stream flows + (SWAT)•Sensitivity analysis calibrated and validated•Simulation model at 2020s, 2050s and 2080s periods to assess the climate scenarios and their impact on water resources system.•Finally, To give a clue and increase awareness on the possible future risks of climate change in order to mitigate the impacts climate change on water resources system.

Key Finding'sScenarios Developed for the Future time series (2011-2100)

• The general trend exhibits rising for temperature and decreasing for total annual precipitation.

Changes in rainfall and temperature at upper awash basin level

Changes in Average annual maximum temperature

• 2020: +0.530C• 2050: +1.180C• 2080: +1.870C

Changes in Average annual minimum temperature

• 2020: +0.580C• 2050:+0.820C• 2080:+2.140C

Also the estimate range is same with results of Girma.M (2012) and IPCC‟s average mean annual temperature across Ethiopia will increase by between 0.9 and 1.1°C by the year 2030 and from 1.7 to 2.1°C by the year 2050.

Basin-average annual rainfall based on the ECHAM5 downscaling

2020: +2.4%2050:-2.14%2080:-10.109%

by using the same model by (Girma.M 2012) point out that the CCLM downscaling resulted in the upper Blue Nile were 1.8, -6.6 and -6.4% in 2011-2040, 2041-2070 and 2071-2100 respectively.

The result of this analysis confirmed also with the IPCC‟s , precipitation show a change of between 0.6 and 4.9% and 1.1 to 18.2% for 2030 and 2050, respectively (NM,A, 2006).

SWAT Hydrological Model ResultsFlow Calibration

Manual calibration (manually and automatically) using observed flow gauged at the outlet of the watershed

flow calibration at the outlet of Hombole and Melka kunture guaging stations

Hombole

Hombole total flow(m3/s) Average flow(m3/s)  

R2

 

ENS

 

Bias

 

RMSE

RVE

Period gauged simulated gauged simulated

1993-20004640.26 3835.30

 39.95

48.34 0.83 0.80 8.38 16.780.320

Melka kunture

1993-20002692.96 3193.511 28.05 33.26

0.90 0.91 9.6 13.40.186

Hombole

Melka kunture

Projected changes in the mean annual and seasonal stream flow

• Generally our results also suggest that the relationship of annual stream flow to annual precipitation may change in a future climate in that a unit decrease in precipitation will cause a larger decrease in stream flow for the year 2050 and 2080.

2020: +4.9%2050:-2.46%2080:-18.14%2020: +2.04%

2050:-9.90%2080:-19.73%

Monthly and annual impacts on future Surface runoff• The future scenario generated runoff shows a decreasing in the

future time series for the two periods from 2050 and 2080 comparing with the base period 1981-2010, but for the future time series 2020 has an increasing in runoff comparing with the base period.

2020: +8%2050:-1.5%2080:-3.52%

2020: +7.49%2050:-0.99%2080:+7.14%

Adaptation StrategiesBased on result of study stream flow and runoff decrease for the future 2050 and 2080 periods, below are some possible adaptation options to be implemented to overcome the reduction stream flow and surface runoff in the watershed :-

Watershed based integrated water resource management approach. Constructing water storage structures to store excess water flowing during rainy season so as to use it for dry season.

Consideration of climate change and its impact at all levels of water resource development projects from the planning up to the execution and management phases.

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ConclusionsFrom the scenario results indicate that an increase in precipitation resulted in an increase in annual runoff and stream flow.

In contrast, a temperature increase caused a decrease in annual runoff. The runoff has a negative correlation with temperature change but a positive correlation with precipitation change.

Generally the analyses carried out in this study revealed that climate change would have a significant impact on the Surface runoff and stream flow, and other hydrological parameter causing a possible reduction on the total water availability in the upper awash sub-basin.

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s ĂƌŝĂďůĞƐ /ŶĐƌĞĂƐĞŝŶĞǀ ĂƉŽƚƌĂŶƐƉŝƌĂƚŝŽŶ

Recommendations

In addition to fluctuations on temperature and precipitation, deforestation and population growth due to industrial expansion in the area are among current trends over the sub- basin.

Hence, it is important to examine the impacts of climate and land use changes over the study area.

It is believed that the results of this study give a clue and increase awareness on the possible future risks of climate change.

This in combination of the future climate change impact on reduction of the available water in the watershed causes a water stress within and around the Sub-basin.

Hence, it is strictly recommended that the adaptation measures proposed in the above section need to be effectively implemented in any existing and development of a new project in the study area.

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THANK

YOU!!!

This work was supported by International Development Research Center (IDRC) through ICTWCC Kenya project funded.