Analysing inter-annual variability of the water-energy balance in the upstream watershed of the Panjiakou Reservoir.

The Panjiakou Reservoir is the largest reservoir on the Luan River, which is a major surface water source, but reservoir inflow has decreased significantly in recent decades. The physical aspect of the hydrological cycle in the upstream of the reservoir is studied to understand the hydrological changes and provide a sound scientific basis of water resources management. In the present research, a distributed hydrological model (i.e. GBHM) and a simple water-energy balance model based on the Budyko hypothesis were used. Using the climate and discharge data of 1980-1991, the present study analyses the inter-annual variability of water balance. The daily discharges at different locations are simulated by the GBHM model, and the actual evapotranspiration is estimated using both the GBHM and water-energy balance model. Comparing the results, both models give similar results that show the same complementary relationship between actual and potential evapotranspiration on an annual time scale.