Characteristics of Evapotranspiration over Nitraria tangutorun Nebkhas in a Desert-oasis Ecotone of Northwest China

Nitraria tangutorun nebkhas can fix huge amount of moving sand and is one of the most effective ways to protect oasis from moving sand in northwest China. However, after the dune is fixed, Nitraria tangutorun gradually dies, which releases the fixed sand and damages the oasis again. The over use of water by evapotranspiration (ET) was assumed to be the reason of dune degradation. It is necessary to accurately measuring the ET to overcome this challenge. In this study, using the Bowen ratio system, ET was measured over Nitraria tangutorun nebkhas in a desert-oasis ecotone of Northwest China, during an entire year (1st January to 31th December 2011). The results showed daily ET rates varied from 0.002-2.58 mm d^-1. The total ET during the growing season (May-October) was 90.44 mm, with a mean value of 0.54 mm, which contributed about 75% of the annual ET in 2011. The Bowen ratio (β) had a clear "U" shape over the course of the growing season. It ranged from 0.9 to 2.6, indicating extremely dry conditions. Cumulative ET (120.8 mm) exceeded precipitation (94.8 mm) during the study period by 27.4%. ET not only consumed all the rainfall in the growing season, but also some of the water stored in the soil, which finally causes the death of Nitraria tangutorun These results will be useful for oasis protection.