Evapotranspiration and water balance of high elevation grassland on the Tibetan Plateau
High elevation grasslands of the Cyperaceae Kobresia pygmaea cover nearly half a million km(2) on the Tibetan Plateau. As a consequence of climate change, precipitation patterns in this monsoon influenced region may change with possible consequences for grassland productivity. Yet, not much is known about the water cycle in this second largest alpine ecosystem of the world. We measured the evapotranspiration of a high elevation Kobresia pasture system at 4400 m a.s.l. in the south eastern part of the plateau in two summers using three different approaches, weighable micro lysimeters, eddy covariance measurements, and water balance modeling with the soil plant atmosphere transfer model SEWAB. In good agreement among the three approaches, we found ET rates of 4 6 mm d( 1) in moist summer periods (June August) and similar to 2 mm d( 1) in dry periods, despite the high elevation and a leaf area index of only similar to 1. Measured ET rates were comparable to rates reported from alpine grasslands at 1500 2500 m a.s.l. in temperate mountains, and also matched ET rates of managed lowland grasslands in the temperate zone. At the study site with 430 mm annual precipitation, low summer rainfall reduced ET significantly and infiltration into the subsoil occurred only in moist periods. Our results show that the evapotranspiration of high elevation grasslands at 4400 m can be as high as in lowland grasslands despite large elevational changes in abiotic and biotic drivers of ET, and periodic water shortage is likely to influence large parts of the Tibetan Kobresia pastures. (C) 2015 Elsevier B.V. All rights reserved.