Hydrological cycle in relation to permafrost environment in forest-grassland ecotone in Mongolia

Abstract

In the mountainous regions of northern Mongolia, there are peculiar different patches of the landscape "ecotone" with north-facing forest slope and south-facing grassland slope. The slopes are distinguished as marked contrast of permafrost distribution as well. The present study revealed ecohydrological processes in terms of evapotranspiration and water balance based on continuous observation since 2004 in the ecotone area of Shiljiree river watershed, upper part of Tuul River in Khentii Mountains. Soil moisture amounts following rainfall during early growing season have primary importance on interannual variations in transpiration from larch forest slope. In addition, timings of snow disappearance and thawing active layer affect subsequent foliation of trees and their transpiration. The estimation of water balance during summer 2006 demonstrated that the larch forest slope with underlying permafrost suppressed the evapotranspiration with half of amounts in grassland slope. It means that precipitation and soil water in forest slope can be partitioned to evapotranspiration and river runoff. On the other hand, grassland at south-facing slope with no underlying permafrost has remarkably large amounts of evapotranspiration and therefore both precipitation and soil water was consumed entirely to evapotranspiration. The results depicted that the coexistence between permafrost and forest in mountain slope has an important role in sustaining water resource.