Simulations of the sensitivities of vegetation succession and surface water balances to climate changes for a sub-alpine basin in the mountain region of Southwestern China
To investigate the responses of vegetation and the surface water balances to climate changes at basin scale in the mountain region of southwestern China,the Biophysical /Dynamic Vegetation Model SSiB4 /TRIFFID was coupled with TOPMODEL. Long-term dynamic simulations were run for the vegetation succession and water balances under different climate scenarios for the Soumou River Basin in the sub-alpine mountain region. The results showed that an increase in temperature alone by 1℃ would result in a reduction in annual runoff depth by 14. 8% - 20. 1%. An increase in precipitation by 10% would increase the annual runoff depth by 19. 8 % - 28. 7%. Temperature rises by 2℃ would result in an increase in evapotranspiration by 28. 9% - 39. 0% and a reduction in annual runoff depth by 39. 9% - 53. 5%; Changes in precipitation alone affected evapotranspiration slightly. The results also indicated that among the three vegetation types of C3 grass,tundra and forest the leaf area index of forest was most sensitive to temperature changes during the growing season. In the sub-alpine mountain region evapotranspiration was very sensitive to temperature changes and was not sensitive to precipitation changes whereas temperature kept unchanged. Runoff was very sensitive to temperature and precipitation changes. Rise in temperature will reduce runoff depth through increase in evapotranspiration. The degree of sensitivity of evapotranspiration or runoff to climate changes was related to the types of vegetation cover. Among the three vegetation types,forest evapotranspiration increases most with increasing temperature owing to a significant increase in water loss through canopy interception evaporation and transpiration. When the basin is covered by forest,evapotranspiration and runoff of the basin are most sensitive to temperature changes.