Evaluation of Climate Change Impact on Extreme Hydrological Event Case study: Addis Ababa and surrounding catchment
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Date
2011-05
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Addis Ababa University
Abstract
The global climate may have serious impact on the frequency, magnitude, location and durations of
hydrological extremes. Change in hydrological extremes will have implications on the design of
future hydraulic structures, flood- plain development and water resource management .This study
assesses the potential impact of climate change on extreme hydrological events in Akaki River
catchment in and around Addis Ababa area. Projection of the future climate variables is done by
using General Circulation Model (GCM) which is considered as the most advanced tool for
estimating the future climatic condition. The climate projection analysis was done by dividing the
coming 90 years into two time periods. The 1990-1999 was taken as baseline period against which
comparison was made. A hydrological model, HEC-HMS was utilized to simulate Runoff in the
study area. The performance of the model was assessed through calibration and validation process
and resulted R2=0.78 during calibration and R2=0.81 during validation.
For the coming 90 years, the mean monthly precipitation may both increase and decrease. The
decrease in mean monthly precipitation may be up to 51% in 2030s and the increase may reach up
to 131% in 2090s. The maximum and minimum temperature indicated an increasing trend. The
simulated result shows that the maximum river flows in the study area will be high and more variable
in terms of magnitude, and irregular of occurrence, than they are at present. It is observed that
climate change has negligible effect on the low flow condition of the Akaki River flow. According
to the evaluated scenarios, climate change has impact on the distributions of hydrological extremes in
the study area. The impact of climate change may also cause a decrease in monthly mean flow up to
41% in the 2030s and increase up to 126% in the 2090s. Seasonal mean flow may show increase up
to 13% and 15% in Kiremt (JJAS) season for 2030s and 2090s time periods respectively. The
increasing of seasonal mean flow in Kermit (JJAS) has its own contribution for occurrence of
flooding in Addis Ababa city. The increase in Bega (ONDJ) season flow will have a paramount
importance for water harvesting in dam of water supply to Addis Ababa city. It is observed that
there may be a net annual increase in mean annual flow volume in Akaki River due to climate
change.
Key words: Climate change; GCM, SDSM, flood; low flow; HEC-HMS; Addis Ababa
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Keywords
Climate Change, Gcm, Sdsm, Flood, Low Flow, Hec-Hms, Addis Ababa