Abstract: Pakistan is among the most vulnerable regions to climate change impacts, in particular the agricultural areas found in the worlds' largest contiguous irrigation system, the Indus River Basin (IRB). This study assesses the impacts of two climate change scenarios (Representative Concentration Pathways-RCPs 4.5 and 8.5) on soil evaporation and transpiration rates, crop water productivity (CWP) and wheat and sugarcane yields over the 21st century, under two irrigation schedules (less/more frequent irrigation and higher/lower volume) for six locations along the Sindh and Punjab provinces. Maximum and minimum temperatures are projected to increase across the study area over the course of the 21st century. Additionally, precipitation is projected to increase (decrease) along the southernmost (northernmost) areas during the summer rainy season from June to September. To evaluate the crop-water productivity of wheat and sugarcane, we used the AquaCrop model in the six selected locations. For assessing the goodness of model validation and calibration, different statistical indicators are considered for comparing simulated and observed inter-annual yield variability (e.g. NRMSE of 12.4% and 12.1% for wheat and sugarcane, average values of the calibration and validation process). Our results show that wheat yields are likely to remain constant over time across the study areas, whereas sugarcane yields are expected to experience a decline in the Sindh province and an exponential increase in the Punjab province up to 2080, then yields will start to decline. In addition, our results reveal that both crops perform better, in terms of CWP, under low frequent irrigation and higher volumes of water. Overall, the findings of this work also support policymakers and project developers to implement adaptation strategies to cope with changing environmental conditions in a country where pressure on water resources is expected to continue to grow.

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