Simulation of daily runoff in Central Asian alpine watersheds

A two-component model of river runoff simulation in alpine regions of Central Asia has been implemented. The first component was devoted to the estimation of daily water input. The second component converts water input to river runoff hydrograph. The method of water input simulation was based on mean daily air temperature and daily precipitation at a reference meteorological station, and on the distribution of air temperature, precipitation, and watershed area as a function of elevation. The runoff simulation method took into account the water retention capacity of the snow, the amount of refrozen melt water, and the ice melt under glacial moraines. The method of hydrograph derivation was based on single- and two-reservoir models. Calibration and validation of the river runoff simulation model were done for the Oigaing and Ala Archa alpine drainage river basins. The runoff hydrograph generation model was calibrated on the basis of daily data for dry, wet, and normal years. The two-reservoir hydrograph model produced minor improvements in prediction as compared with the single-reservoir runoff hydrograph method. Simulation errors increased with increasing annual river runoff and depend on snowmelt, glacier runoff, the amount of precipitation, and air temperature. The simulated river runoff was less than observed values during autumn–winter. In the Ala Archa river basin, where glacier melt is a significant component of river runoff, and in years with large glacier melt, the simulated river runoff underestimated observed values.