Application of Different Evapotranspiration Models to Calculate Total Agricultural Water Demand in a Tropical Region

Today, water in the Long Xuyen Quadrangle-An Giang (LXQAG)(Mekong River delta, Vietnam) is becoming scarce in some seasonsand some districts in the region, especially when the scenariosof climate change will affect water resources in the future.Therefore, it is necessary to make decisions about water conservationand distribution to ensure compatibility with the socialobjectives such as economic efficiency, sustainability and fairness.The mathematical models used for water distribution andbalance calculations are the prominent themes nowadays. To performthis task, it needs to calculate the water needs for all economicsectors. In this article we are particularly concerned aboutwater demand calculation methods for crops and aquaculture.Because these are the two main commodities accounting for thehighest water usage in the region. Water demand for crops is calculatedthrough potential evaporation using the methods of Hargreaves& Samani; Priestley and Taylor and Penman-Monteithto check if the first two simpler methods with less data demandcould be used to estimate evapotranspiration. The results showthat the simpler methods were significantly different and thereforewater demand calculations must be based on the Penman-Monteith method for the water demand of crops and the methodsof Penman to calculate expansion evaporation for aquaculture.The result shows that the total water demand in 2015 is 6,428million m³/year. It is estimated that in 2020, agricultural waterdemand will rise by 71% compared to 2015 to 22,531 millionm³/year. The main reason for this rise is that the local managersexpect the catfish farming area to increase by 80%, if peopleapply the “VietGAP standards”.