Quantifying water and energy budgets and the impacts of climatic and human factors in the Haihe River Basin, China: 1. Model and validation

- A water/energy flux model considering human and sub-grid effects is developed.
- The developed model is validated using multi-source observations.
- The model can be applied to the quantitative study of regional water/energy budget.
- Spatial and temporal variations in water/energy budgets in the HRB are analyzed.
- Irrigation made water deficit and groundwater level rapid decline in the plains.

SummaryWe have developed an operational model to simulate water and energy fluxes in the Haihe River Basin (231,800 km2 in size) for the past 28 years. This model is capable of estimating water and energy fluxes of irrigated croplands and heterogeneous grids. The model was validated using actual evapotranspiration (ETa) measured by an eddy covariance system, measured soil moisture in croplands, groundwater level measurements over the piedmont plain and runoff observations in a mountainous catchment. A long-term time series of water and energy balance components were then simulated at a daily time step by integrating remotely sensed information and meteorological data to examine the spatial and temporal distribution and changes in water and energy fluxes in the basin over the past 28 years. The results show that net radiation (Rn) in the mountainous regions is generally higher than that in the plain regions. ETa in the plain regions is higher than that in the mountainous regions mostly because of higher air temperature and larger areas of irrigated farmland. Higher sensible heat flux (H) and lower ETa in the urban areas are possibly due to less vegetation cover, an impervious surface, rapid drainage, and the heat island effect of cities. During the study period, a water deficit continuously occurred in the plain regions because of extensive pumping of groundwater for irrigation to meet the crop water requirements. Irrigation has led to significant groundwater depletion, which poses a substantial challenge to the sustainability of water resources in this basin.