Surface energy fluxes and controls of evapotranspiration in three alpine ecosystems of Qinghai Lake watershed, NE Qinghai-Tibet Plateau

Qinghai Lake watershed, located in the northeast of the Qinghai-Tibet Plateau, is a region that is sensitive and vulnerable to global climate change. Both the hydrological cycle and water balance in a watershed are significantly influenced by surface energy fluxes and evapotranspiration (ET); however, there is limited information related to the water and heat fluxes in this area. Using the Bowen ratio energy balance method, we measured surface energy fluxes and ET and then explored their controlling factors in three typical ecosystems of the Qinghai Lake watershed, i.e. Kobresia meadow (KMd.), Potentilla fruticosa shrub (PFSh.) and Achnatherum splendens steppe (ASSt.) between 2012 and 2013 for the first time. It was found that between the different ecosystems, there were large differences in the energy portioning. Annual sensible and latent heats accounted for 56-64% and 35-45% of net radiation, respectively. The Bowen rations were the highest in the ASSt. site and the lowest in the PFSh. site. The Bowen ratios and soil water content had negative correlations. Annual ET was 507.9, 493.2 and 413.7mm for the PFSh., KMd. and ASSt. sites, respectively. The annual ET in the KMd. and PFSh. sites was 16% and 3% less than the annual precipitation, while the ET was 26% higher than precipitation for the ASSt. site. Fluctuations in the daily ET of alpine ecosystems from the Qinghai Lake watershed were primarily controlled by radiation, especially during the growing season, whereas ET was also controlled by soil water content in the ASSt. ecosystem where precipitation was low. Copyright (c) 2015 John Wiley & Sons, Ltd.