Distributed modeling of landsurface water and energy budgets in the inland Heihe river basin of China

A distributed model for simulating the land surface hydrological processes in the Heihe river basin was developed and validated on the basis of considering the physical mechanism of hydrological cycle and the artificial system of water utilization in the basin. Modeling approach of every component process was introduced from 2 aspects, i.e., water cycle and energy cycle. The hydrological processes include evapotranspiration, infiltration, runoff, groundwater flow, interaction between groundwater and river water, overland flow, river flow and artificial cycle processes of water utilization. A simulation of 21 years from 1982 to 2002 was carried out after obtaining various input data and model parameters. The model was validated for both the simulation of monthly discharge process and that of daily discharge process. Water budgets and spatial and temporal variations of hydrological cycle components as well as energy cycle components in the upper and middle reach Heihe basin (36 728 km<sup>2</sup>) were studied by using the distributed hydrological model. In addition, the model was further used to predict the water budgets under the future land surface change scenarios in the basin. The modeling results show: (1) in the upper reach watershed, the annual average evapotranspiration and runoff account for 63% and 37% of the annual precipitation, respectively, the snow melting runoff accounts for 19% of the total runoff and 41% of the direct runoff, and the groundwater storage has no obvious change; (2) in the middle reach basin, the annual average evapotranspiration is 52 mm more than the local annual precipitation, and the groundwater storage is of an obvious declining trend because of irrigation water consumption; (3) for the scenario of conservation forest construction in the upper reach basin, although the evapotranspiration from interception may increase, the soil evaporation may reduce at the same time, therefore the total evapotranspiration may not increase obviously; the measure of changing the farmland to pasture land in the middle reach basin has obvious effects on decreasing evapotranspiration, increasing the discharge at Zhengyixia, and decreasing the storage deficit; reducing the irrigation surface water use in the middle reach basin has obvious functions on increasing the discharge to downstream but the groundwater exploitation increasing should be restricted to prevent the groundwater table decline.