Theories and calculation methods for regional objective ET (evapotranspiration): Applications

The regional objective ET (evapotranspiration) is defined as the quantity of water that could be consumed in a particular region. It varies with the water conditions and economic development stages in the region. It is also constrained by the requirement of benign environment cycle. At the same time, it must meet the demands of sustainable economic growth and the construction of harmony society. Objective ET based water resources distribution will replace the conventional method, which emphasizes the balance between the water demand and the water supply. It puts focus on the reasonable water consumption instead of the forecasted water demand, which is usually greater than the actual one. In this paper, we calculated the objective ET of 2010 year level in Tianjin by an analysis-integration-assessment method. Objective ET can be classified into two parts: controllable ET and uncontrollable ET. Controllable ET includes the ET from irrigation land and the ET from resident land, among which the former can be calculated with soil moisture model and evapotranspiration model, while the latter can be calculated by water use ration and water consumption rate. The uncontrollable ET can be calculated with the distributed hydrological model and the remote sensing monitoring model. The two models can be mutually calibrated. In this paper, eight schemes are put forward based on different portfolios of water resources. The objective ET of each scheme was calculated and the results were assessed and analyzed. Finally, an optimal scheme was recommended.