Estimating the water and heat budget as an indicator for water resources management using an integrated watershed modeling tool

A water resources management considering not only water but also heat has become a crucial issue due to limited availability of water resources, increasing water contaminations and ground source heat utilizations. Indicators are useful to manage water resources. Water budget and Heat budget can be one of the major indicators for sustainable water resources management because detecting the disequilibrium of these budgets at an early stage makes it possible to implement effective measures. However, many components required to estimate these budgets in a domain that include the surface and the subsurface are difficult to measure directly, for instance, the water and heat transported by recharge, and the groundwater discharge in a regional watershed scale. An integrated watershed modeling technique allows to represent seamlessly the mass and heat transport behaviors from the surface to the underground in arbitrary temporal and spatial scales. Moreover, a spatiotemporal water flow behavior can be expressed without any explicit conditions for routing the paths of water movement. Therefore, this kind of modeling technique becomes efficient tool to estimate the components of these budgets. First, the framework for estimating these budgets using an integrated watershed modeling tool is proposed in this study as follows: • Collecting available data such as meteorology/ocean conditions, land use/land cover, topography, soil/geology, water use/heat utilization and monitoring data • Associating these data with model parameters like porosity, heat conductivity and rainfall conditions • Model construction by assigning parameters to each discretized mesh and calibration through comparison with monitoring data • Estimating the water and heat budget Then, the water and heat budget components which are classified into inflow and outflow for the surface and the subsurface domains are described. Additionally, the following applications to estimating the components of the water and heat budget using actual watershed models in various scales are presented briefly: • Estimation of the recharge rate of whole Japan using a national-scale watershed model • Water budget estimation using regional-scale watershed models • Feasibility study of ground source heat utilization in a local-scale urban area In order to perform the water and heat budget estimations more rapidly and with minimal cost, the authors are challenging the development of new data models updated continuously and re-used efficiently. The challenge in this domain is to provide information immediately to help the decision-making for watershed management.