Evapotranspiration and water balance of high-elevation grassland on the Tibetan Plateau
2016
Coners, Heinz | Babel, Wolfgang | Willinghöfer, Sandra | Biermann, Tobias | Köhler, Lars | Seeber, Elke | Foken, Th. | Ma, Yaoming | Yang, Yongping | Miehe, Georg | Leuschner, Christoph
High-elevation grasslands of the Cyperaceae Kobresia pygmaea cover nearly half a million km2 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 4400m 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 4–6mmd−1 in moist summer periods (June–August) and ∼2mmd−1 in dry periods, despite the high elevation and a leaf area index of only ∼1. Measured ET rates were comparable to rates reported from alpine grasslands at 1500–2500m a.s.l. in temperate mountains, and also matched ET rates of managed lowland grasslands in the temperate zone. At the study site with 430mm 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 4400m 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.
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