A distributed runoff model for the mountainous region of the Heihe River Basin (China) based on the spatial modeling environment (SME) II model calibration and validation

The generality of the Christiansen model is verified using potential evaporation data as reference for the unit model developed in stella. The spatial model in SME is calibrated with data from six hydrological and meteorological stations around the study area. The results show that the observed and simulated data have a good fit, in which the revised Nash–Sutcliffe efficiency (NSE), balance error (B), and explained variance (EV) are 0.56, −0.2, and 0.55, respectively. The best fit is seen in autumn and winter; for spring, the actual values are generally higher than in simulated observations. The spatial model can simulate the majority of summer peaks, but some are not simulated well. Running the model under different spatial resolutions shows a certain degree of stability, with the revised NSE ranging from 0.29 to 0.50. As spatial resolution increases, the simulation NSE values behave non-linearly. With the other parameters unchanged the impact of human activities, which is represented by climate change scenarios on the hydrological process, is analyzed. Assuming constant temperature, precipitation has a greater influence on runoff than on evaporation; while when precipitation is constant, evaporation is influenced more by temperature. Although the model can validate the effect of climate change on runoff and evapotranspiration, it is not enough to describe the complex relationship between runoff, evaporation, temperature, and precipitation accurately, because the description of the water cycle process is simplified compared with a highly specialized hydrological model. The water and heat coupling process is not included in the soil freezing and thawing process; the source code of SME needs to be deeply understood to improve the algorithms of interpolation and conflux. More importantly, the current work does not consider the impact of human activities endogenously. The main purpose of this paper is to build a better basis for developing a meaningful integrated ecological economic model in the Heihe River Basin to solve its ecological and economic problems.