Abstract:
The study carried out in Didessa watershed, one of the largest tributary of Blue Nile River in
terms of volume of water, which is situated in the south-west part of Abay river basin. Due
to its great importance of the basin by many criteria, so it was crucial to undertake a research
to evaluate the potential impacts of climate change on the water resources availability. In
this study because of lack of availability of data it is difficult to consider the whole
catchment, only the upper Didessa catchment is considered for the study which wastaking the
outlet gauging station at near Arjo town (9981km
2
).Future Climate change scenarios of
precipitation and potential evaporation were developed using output of dynamically
downscaled of ECHAM5 (GCM) under A1B emission scenario condition at 2020’s (2031-2040) and at 2080’s (2091-2100).The projected future climate variable showed an increasing
trend from the 1991-2000(base period) level. It is estimated that the average seasonal and
annual potential evaporation in the watershed at 2020’s might increase up to 5.2% and 4%
respectively and in 2080’s the average potential evaporation might increase up to 15.85%
seasonally and 12.66% annually. Besides, at 2020’s it is exhibited that the average seasonal
precipitation might increase from 12.14% up to 62.79% and annually 30.22% .The maximum
increment is observed during spring whilethe minimum in autumn. In the other time horizon, in
2080’s the average seasonal precipitation might vary from -10.29% up to 25.29%, maximum
increase in autumnwhere as the only reduction is observed during springseason.
These changes of climate variables were used as input to the HBV hydrological model
which was calibrated (R
2
=0.601) and validated (R
2
=0.61) with historical data to investigate
the potential impacts of climate changes in the catchment. The simulation results obtained
from the investigation indicated that there was a significant variation in the seasonal and
monthly flow in both future period scenarios. At 2020’s seasonally as well as monthly
positive incremental change is observed, during the main rainy season (summer) the
percentage changes might reaches up to 157%.At 2080’s the average monthly flow only
during the month of April showed 12% reduction, in the rest of the months a great increment
is exhibited, the average seasonal flow also showeda significant increment during summer,
136% in respect to the base period. Hence, in Didessa watershed, runoff is likely to increase
in the future.
