Application of different evapotranspiration models to calculate total agricultural water demand in a tropical region

Abstract

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