Storing flood water and subsequently using it for rice-based upland crop production in the dry season is an issue for sustainable agriculture in the Mekong Delta of Viet Nam. An on-farm trial, conducted in between August – December 2015 in the Chau Phu district of An Giang province, was conducted to determine irrigation requirement and water use efficiency of chilli pepper that could replace a rice crop in the dry season in the flood-prone areas for higher water use efficience. Irrigation requirement and yields of chilli were simulated by using the AquaCrop software (version 4.0) with various varieties for air temperatures and water irrigation level. Results showed that simulated yield of chilli pepper was 6.13 ton per hectare, and this simulated yield was similar to the practical harvesting yield of chilli pepper (6.33 ton per hectare). This water volume accounted for 59% of output components of the water storage. The study revealed that changes in rainfall and temperatures significantly influence irrigation requirement and the yield of chilli pepper. Irrigation requirement is expected to increase as the temperatures rise. Irrigation requirement is expected to increase as the rainfall reduce. Further studies for other crops and ways of how to reduce pond storage water losses by evaporation and seepage are necessary.