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 net irrigation requirement (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.
