CLIMATE CHANGE IMPACT ASSESSMENT ON RUNOFF POTENTIAL IN  UPPER AWASH BASIN: A CASE STUDY OF LEGEDADI - DIRE CATCHMENT
Creators: name: TSEGA WOLDESELASSIE
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2015

description: Climate  change  is  a  global  challenge.  It  is  known  regional  hydrology  is  influenced  by 
global climate change, through changes in patterns  of precipitation  temperature, runoff 
and other hydrologic variables.  This has  serious  consequences on societal development 
and the costs of achieving adequate levels of water security.  In this study climate change 
impacts  on  runoff   water  potential  at  catchment  scale  for  the  two  selected  catchment  in 
Upper Awash Basin have  been assessed. The two catchments included in the study were 
Legedadi  (205  Km
2
)  and  Dire  (77.56  Km
2
)  catchments.  A  0.44°  resolution  data  of 
Coupled Model Inter-comparison Phase5 (CMIP5) global climate models (GCMs) output 
of  precipitation  and  temperature  (max&amp;  min)  for  2020’s  (2016-2035),  2050’s  (2046-2065)  and  2080’s  (2081-2100)  under  (RCP  4.5)  were  applied  to  assess  the  climate 
change  scenarios.  Bias  correction  was  applied  to  these  forcing  variables.  Moreover,  a 
hydrological  model,  Arc-SWAT,  was  utilized  to  simulate  runoff  in  the  study  area. 
Sensitivity analysis result  shown that  Curve  Number  (CN)  factor are the  most  sensitive 
parameters  affecting  the  hydrology  of  the  catchments.  The  model  was  calibrated  from 
1988-1997 and validated from 1998-2003 at the  estimated outlet of Legedadi and Dire 
catchment.  In  terms  of  hydrological  modeling  performance,  at  both  catchments  (NSE) 
indices are greater than 0.8  and  0.85 for calibration and  validation period  respectively.
Future projections  results  as compared  to base period (1986-2005)  have shown that, the 
annual  precipitation  exhibit  an  increasing  trend.  Maximum  increment  is  observed  for 
2050s  projection  with  +11.9%  at  Legedadi  and  11.3%  at  Dire.  The  seasonal  rainfall 
increment  is  more  pronounced  at  2050`s  than  2020s  and  2080s  at  both  catchments,
higher increment is observed on season (JJAS) at 2050s,  decrement  is on season  FMAM 
at Legedadi and ONDJ at  Dire  it ranges  (+18.5%  &amp;  -13.1% at Legedadi) and  (18.6% 
and  -68.1% at  Dire)  at 2080s.    The mean  daily  temperature increases  for future periods 
(2020`s, 2050’s, and 2080`s)  with maximum increment of  +17.7% in 2080s. In general in 
both  study  catchments;  the  impact  of  climate  change  may  cause  an  increase  in  annual 
runoff  for  future  periods.  It  may  rise  up  to  14.3%  in  Legedadi  and  17%  in  Dire 
catchments in  the 2050s.High  Seasonal mean runoff may  be  observed  at  Kiremt  season 
and  high  radiation  may  be  observed  on  Bulge  season.  It  ranges  (+20%and  -32% 
Legedadi)  (+23.9%  &amp;  -51.9%  Dire).  The  sensitivity  analysis  has  shown  that  both 
catchments are more sensitive to rainfall. The increase in runoff magnitude may probably 
have positive impacts in meeting the water supply demands to Addis Ababa city.