Abstract:
In this study, impact of climate variability and climate change on Koga irrigation scheme has been
evaluated. In addition, appropriate climate change adaptation options for this irrigation scheme
have been evaluated through stakeholder consultation. A single level – stakeholder consultation
was undertaken to prioritize and select the best adaptation options using a Multi- Criteria- Analysis
(MCA) and scenario analysis method. The HBV rainfall runoff model was used to quantify inflow
to Koga reservoir. The Water Evaluation And Planning model (WEAP) was applied to evaluate the
impacts of climate variability and change on the reservoir and irrigation scheme. WEAP was set
up for the designed and operational cropping patterns. High resolution (50km) and bias corrected
outputs of dynamical downscaled data from three climate models (GFDL, NORESM and MPI)
were used to derive inputs to HBV and WEAP. The climate scenario is the Representative
Concentration Pathways (RCPs) 4.5. Under the designed cropping pattern the reliability of the
Koga dam is 98.77% and meets almost 100% of the irrigation demand on annual basis. The
demand coverage is small in May and June which is only 96.33% and 98.46% respectively. The
reliability and coverage of the Koga dam did not change when the designed cropping pattern is
replaced with the operational cropping pattern. The NIR is expected to increase in all models due
to climate change. Under the GFDL model the largest NIR is seen on the designed crop pattern
than operational cropping pattern. Beside this the reservoir inflow is projected to decrease due to
the reduction of rainfall amount and high amount of net evaporation by GFDL and MIP but, in
NORESM the inflow will not significantly change. According to farmers and experts, the best
options to deal with possible impacts of climate change are to shift to crops that require relatively
less amount of water or less frequent irrigation, use short duration crop varieties and water
allocation that takes in to account the development stage of the crops.
