The energy-limited water loss of an alpine shrubland on the northeastern Qinghai-Tibetan Plateau, China

Study region: Alpine shrubland on the northeastern Qinghai-Tibetan Plateau. Study focus: Water provision ability is a pivotal ecological service of high-altitude alpine regions and is controlled by precipitation, evapotranspiration (ET), and soil water storage whereas the underlying ecohydrological processes remain highly unquantified. Here, we investigated continuous 19-year flux measurements to quantify the temporal patterns of ET and water budget (precipitation minus ET, P-ET), as well as 0-20 cm soil water storage change (Delta SWS). New hydrological insights for the region: At a monthly scale, ET peaked in July (96.7 f 26.4 mm, Mean f S.D.) and averaged 41.7 f 31.9 mm, whose variations were determined by the slope of the saturation vapor pressure curve at air temperature, air and soil temperatures, regardless of vegetation growth stage. P-ET averaged 18.3 f 26.3 mm in August and September while stayed deficit during the other months. The variations in P-ET were controlled by precipitation in the May-October growing season whereas by ET in the non-growing season from November to April. Delta SWS peaked in May (28.8 f 11.2 mm) and September (3.0 f 2.7 mm) and almost accumulated to zero over the whole season. At annual scales, none of ET, P-ET, and Delta SWS changed significantly. ET averaged 512.2 f 68.4 mm and exceeded precipitation (459.1 f 58.4 mm), likely due to the lateral flow supply of uphill locations. The variations in ET were regulated directly by bulk canopy resistance and indirectly by net radiation. P-ET averaged -53.2 f 95.4 mm and demonstrated a clear water deficit (-51.6 f 21.0 mm) during the non-growing season. The variations of P-ET were driven jointly by precipitation and ET, with opposite but equivalent effects. The dominance of thermal conditions and energy availability on ET variability manifested an energy-limited feature of water loss in the alpine shrubland. The temporal patterns in P-ET elucidated that the alpine shrubland plays the water retention rather than water provision function through transforming variable precipitation input into stable ET loss.