Modeling of the Hydrological Cycle of a Forest River Basin and Hydrological Consequences of Forest Cutting

ABSTRACT

Physically based model of the hydrological cycle of a forest basin was developed. The model includes description of processes of liquid water and snow interception by forest canopy, snow accumulation and melt, vertical soil moisture transfer and evapotranspiration, overland, subsurface and channel flow. The case-study has been carried out on the basis of experimental observations on the Valday water balance station, situated in the north-western part of Russia. The model has been calibrated and validated using 5-year hydrometeorological observations at the completely forested Tayozhny Creek experimental basin. Then the 17-years hydrometeorological observations were used to estimate the possible change of hydrological cycle of this basin after forest cutting. The numerical experiments have shown that the averaged snow water equivalent before snowmelt for the Tayozhny Creek basin can increase in case of forest cutting by 15%. The snow sublimation losses can decrease almost twice .The snowmelt rates after forest cutting turned out to be about 30% larger and the duration of snowmelt, on average, on 10 days longer. The simulated annual runoff from the Tayozhny Creek basin (mainly of snowmelt origin) averaged for 17 years appeared to be only about 10% higher than in case of forest cutting. However, its seasonal distribution and water balance components changed essentially. The spring flood peak discharge from the forested basin appeared to be, on average, 50% lower, the spring floods started 5-7 days later and the flood recession turned out to be much longer. About 80% of the total runoff from the Tayozhny Creek basin is now subsurface flow, while in case of deforestation overland flow may become dominant. The numerical experiments were carried out to estimate the sensitivity of the hydrological cycle to changes of leaf area index as a forest age characteristic. The estimates obtained by simulation are quite consistent with the estimates obtained on the basis of experimental research.