Study area

The model was evaluated through the application to the Yellow River basin of China. The Yellow River is the second longest river in China. The headwaters of the Yellow River begin on the Tibetan Plateau and the river flows eastward, passing though the Loess Plateau and the North China Plain before emptying into the Bohai Gulf (Figure 2). The river flows 5464 km in distance in the main course and has a river basin area of 794,712 km². The Yellow River has been facing serious water problems, such as water shortage and eco-environmental degradation (Feng et al., 2005; Xu et al., 2002). In particular, the lower Yellow River has suffered from drying up phenomenon since the 1970s. The Yellow River study has been a hot topic in hydrology in China, attracting focus from many researches (Xu, 2005; Yang et al., 2004; Fu et al., 2004; Xia et al., 2004; Liu and Zheng, 2004).

There are several irrigation districts inside the river basin, such as Qingtongxia, Hetao irrigation districts (Figure 2). In addition, there are large irrigation districts in the lower reach, which are located outside the watershed and extract irrigation water from the Yellow River(Chen et al., 2002; Fu et al., 2004). Liu and Zhang (2002) gives a description of the irrigation states in the river basin.

Discharges of eight major hydrologic gauges at the main stream of the Yellow River, Tangnaihai (TNH), Lanzhou (LZ), Qingtongxia (QTX), Toudaoguai (TDG), Longmen (LM), Sanmenxia (SMX), Huayuankou (HYK) and Lijin (LJ) stations (Figure 2) were used to validate the model and analyze the subgrid variability impact to stream flow. The watershed above the Tangnaihai station is the source region of the Yellow River. The water withdrawals from the river are limited in this region. The Qingtongxia station is after the river flows through a large irrigation district (the Qingtongxia irrigation district). The Toudaoguai station is after another large irrigation district (the Hetao irrigation district). The Lanzhou-Qingtongxia and Qingtongxia-Toudaoguai sections are "net" water consumption zone of the Yellow River, i.e. the annual discharge at the Qingtongxia station is less than that at the Lanzhou station and the discharge at Toudaoguai station is less than that at the Qingtongxia station. The Huayuankou station is another key station at the main stream. The annual discharge at this station reaches the maximum value through the river main stem. The Lijin station is the last hydrological station before the river emptying into the Baohai Gulf. Between Huayuankou and Lijin station, the runoff into the river channel is slight because the elevation of the riverbed is higher than the land surface behind artificial levees. In addition, there are large irrigation districts in the lower reach, which are located outside the watershed and channeled river water (Chen et al., 2002; Fu et al., 2004). It is another "net" water consumption zone of the Yellow River.

Figure 2: The Yellow River basin

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