Simulation models like the FAO-AquaCrop can be employed for estimation of crop yield, as they are being used for optimization of crop-production management and planning [11, 12, 13, 14]. Water use and yield response for a wide range of crops and climates around the world have been simulated using AquaCrop model [15, 16, 17, 18, 19, 20, 21]. The impacts of climate variables (i.e., minimum and maximum temperatures, rainfall) on rice yield and variance of the impact during the main season and off-season were assessed in rice granary areas in Malaysia [22]. The model results for both crop seasons were unaffected by rainfall. But rice yield was found to be negatively correlated with the maximum temperature during off-season, and the minimum temperature was found to exert a positive impact on both crop seasons. A comprehensive review [23] highlighted that WP is an important indicator for evaluating water-saving and water investments for farmers and irrigation practitioners. This review assessed the impacts of climate change on crop yield using climate, water, and crop-yield models to give a better understanding of how climate change influences crop yield. The findings show that availability of water and crop yield are expected to decline in the future due to rising temperatures and fluctuating rainfall [23]. Crop-water productivity is affected by climate change in many ways; uncertainty in predictions by the global climate models is one of the reasons, particularly in terms of climate variability [24]. To avoid or mitigate the negative effects of climate change, the quantitative assessment of crop yield and crop-water productivity in response to future climate change is crucial [25]. Crops will be more vulnerable to climate change under the RCP8.5 emission scenario in the Mille and Shandan counties in China than crops in other parts of the country. The FAO-AquaCrop model simulates crop-water productivity, which represents the response of yield to water using several parameters and input data [26]. This model was used to simulate the WP of paddy rice in both humid and semi-arid regions of Iran. The results showed that in a dry climate, evaporation losses contribute to reductions in WP. Several researchers have tested the AquaCrop model to simulate a rice yield response to water in various climates [27, 28, 29, 30, 31]. The temperature projection for Malaysia expects the country to begin warming by end of this century. Rainfall has been projected to decline by 20-40% during off-season (January to June) and increase by the same magnitude during the main season (July to December) across most regions of the country [32]. The warming climate will likely alter cloudiness, windiness, and humidity, all of which control the evaporative demand of atmosphere. The fluctuations in climate variables can bring the agriculture system under serious threat with a resultant stress on agricultural productivity. Elevated concentration of greenhouse gases, especially CO\({}_{2}\), also has direct control on the growth and productivity of crops. Although climate change could reduce rice yields in some regions of the world (e.g., Mekong River Delta, Vietnam), the likely increased CO\({}_{2}\) fertilization may augment the yields and reduce the transpiration rate by suppressing stomatal conductance in most crop species [33]. The study found that plants in warm environments or during droughts can increase their stomatal conductance in response to increased CO\({}_{2}\) while also increasing their water use efficiency compared to plants in temperate latitudes that grow in cooler moist conditions. This study aims at determining how climate change influences WP of irrigated paddy rice using a FAO-AquaCrop model in a tropical climate in Malaysia.