Measurement and estimation of the summertime daily evapotranspiration on alpine meadow in the Qilian Mountains, northwes
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ORIGINAL ARTICLE
Measurement and estimation of the summertime daily evapotranspiration on alpine meadow in the Qilian Mountains, northwest China Yong Yang • Rensheng Chen • Chuntan Han Wenwu Qing
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Received: 9 April 2011 / Accepted: 9 August 2012 / Published online: 24 August 2012 Ó Springer-Verlag 2012
Abstract Research on mountain evapotranspiration (ET) is important to help understand water cycling and predict streamflow in cold regions in China. Actual daily ET was measured in two types of micro-lysimeters with depth 40 cm and diameter 31.5 cm (A) and depth 27 cm and diameter 27 cm (B), from 1 July 2007 to 10 September 2007, on an alpine meadow in the Qilian Mountains in northwest China, where Bowen ratio measuring instrument and eddy covariance system are too costly and difficult to be built in the region. The results of micro-lysimeters were used as a way to calibrate and test a number of energy balance methods and determine the pan coefficient (Kp) for a mountainous site. The results indicate that the FAO-56 Penman–Monteith offers the best performance, with RMSE of 0.61 mm day-1, MAD of 0.46 mm day-1, and the index of agreement near 1, followed by ASCE Penman–Monteith, Priestley–Taylor and Hargreaves–Samani, and the Kp is estimated as 0.7 for the summertime. Keywords Evapotranspiration Micro-lysimeter Penman–Monteith Priestley–Taylor Hargreaves–Samani Pan coefficient
Introduction Evapotranspiration (ET), which represents the combined evaporation from the soil surface and transpiration from
Y. Yang (&) R. Chen C. Han W. Qing Heihe Upstream Watershed Ecology-Hydrology Experimental Research Station, Cold and Arid Region Environment and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China e-mail: [email protected]
plants (Thornthwaite and Mather 1951), is a central element of the hydrological cycle, governing the moisture transfer to the atmosphere and thereby influencing fundamental properties of terrestrial ecosystems such as runoff, soil moisture and plant growth (Thomas 2008). The measurement and estimation of ET with a variety of methods have a long history of application at a diversity of sites (e.g., Gupta and Sastry 1986; Pauwels and Samson 2006; Zhou and Zhou 2009). However, most of reported ET studies in cold regions are in high latitudes, such as the permafrost (Matsumoto et al. 2008) or wetland tundra (Raddatz et al. 2009). The role of ET as an integral part of the water cycle under cold highmountain conditions is still incompletely understood (Jong 2005; Kang et al. 2008), despite the fact that these sites contain the headwaters of many rivers (Yang et al. 2000). The cold region in China, defined as the regions including permafrost, glacier and a great majority of stable seasonal snow cover area (Chen et al. 2006), is about 417.4 9 104 km2, comprising 43.5 % of the country’s land area (Chen et al. 2006). Besides the northeast plain, most of the cold regions are in the high-altitude mountain Qinghai-Tibet Plateau and its neighborhood. Alpine meadow eco
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