An increase in abnormal climate change patterns and unsustainable irrigation in uplands cause drought and affect agricultural water security, crop productivity, and price fluctuations. In this study, we developed a soil moisture model to project irrigation requirements (IR) for upland crops under climate change using estimated effective rainfall (ER), crop evapotranspiration (ETc) and the IR of 29 major upland crops in South Korea. The temperature and precipitation will increase, but the ER is projected to decrease under climate change. ETc and the net irrigation requirement (NIR) are expected to increase under climate change. Vegetable crops have less ER and more NIR than cereal crops with a similar amount of ETc, which means they are more sensitive to water scarcity and IR than cereal crops. In addition, we found that barley has the smallest daily ETc and IR but the highest increase rate in NIR under climate change, especially in the central part of South Korea. The NIR of Chinese cabbage-fall is the lowest in the northern region and increases moving southwards. The NIR of spinach is projected to increase gradually from the southern and eastern coastlines to the northern inland area. Onions have the largest ETc and NIR of the 29 upland crops, but they show small changes compared to other crops under climate change. Water scarcity is a major limiting factor for sustainable agricultural production. The variation of IR and ETc values for each crop under different climate change scenarios depends on the crop, soil, space, and meteorological characteristics. The results of this study can be used as a guideline for irrigation and soil water management for upland crops under climate change.