Modelling water futures using food security and environmental sustainability approaches

Global water scarcity is becoming a constraint for human development. Therefore there is a need to enhance water productivity of the irrigated and rainfed agriculture to meet the increasing food demand due to the population growth. This paper describes modeling efforts to assess present and future water needs for food, people and environment. This exercise is being carried out by the International Commission on Irrigation and Drainage (ICID) in five countries, China, Egypt, India, Mexico, and Pakistan, which together cover 51% of irrigated area and 43% population in the world. This paper presents two modeling frameworks including the food security approach of the International Water Management Institute (IWMI) through policy dialogue model (PODIUM), an environmental approach i.e. the Basin wide Holistic Integrated Water Assessment (BHIWA) model and its system dynamic version using VenSim environment. The two modeling approaches i.e. the BHIWA and PODIUM can be used to simulate and analyze the impacts of land use and climate change impacts on water resources and eventually optimize the water allocations among agricultural, industrial, domestic, and environmental sectors within a basin context. Both approaches described in this paper have shortcomings for exploring water futures of a country. BHIWA is not a distributed hydrologic model and cannot deal with each land use geographically distributed throughout the basin. All such parcels need to be conceptually lumped into a single land use unit. BHIWA model does not depict the spatial variations in rainfall, potential evapo-transpiration, intensities of cropping or irrigation as well as slow horizontal groundwater movement, from under one area to another. The PODIUM model is based on accounting of more or less fixed contemn of “utilizable” surface and ground water resource. The changes in the hydrology due to land use changes, and the resultant changes in the utilizable water are important when considering longer term scenarios. This paper highlights the benefits and disadvantages of using these approaches through model applications in the Qiantang River basin in China. The Qiantang River basin lies in the southeast of China and comes under a subtropical monsoon climate with four well-marked seasons. The average annual precipitation is between 1200 mm and 2200 mm, with annual evaporation ranging between 800 mm and 1000 mm. on the basis of the model simulations presented in this paper it is concluded that the PODIUM model is strong at representing basin/country's food needs and associated use of “utilizable” surface and ground water resources but it does not depict the inter-relations between different hydrologic components e.g. surface and ground water. The BHIWA model developed by ICID aims to quantify water use by three sectors (i.e. nature, food and people), therefore allows better understanding of impact of land use changes as well as soil and water conservation policies and programmes through the simulation of overall hydrologic cycle. A system dynamics based representation of BHIWA model allows users to conceptualize, document, simulate, analyze, and optimize water management. It can help to understand the most sensitive parameters for improving the water use efficiency at system scale.