Evapotranspiration of an oasis-desert transition zone in the middle stream of Heihe River, Northwest China

Abstract

As a main component in water balance, evapotranspiration is of great importance for water saving and irrigation-measure making, especially in arid or semiarid regions. Although studies of evapotranspiration have been conducted for a long time, studies concentrated on oasis-desert transition zone are very limited. On the basis of the meteorological data and other parameters (e.g. leaf area index (LAI)) of an oasis-desert transition zone in the middle stream of Heihe River from 2005 to 2011, this paper calculated both reference (ET 0) and actual evapotranspiration (ET c) using FAO56 Penman-Monteith and Penman-Monteith models, respectively. In combination with pan evaporation (E p) measured by E601 pan evaporator, four aspects were analyzed: (1) ET 0 was firstly verified by E p; (2) Characteristics of ET 0 and ET c were compared, while the influencing factors were also analyzed; (3) Since meteorological data are often unavailable for estimating ET 0 through FAO56 Penman-Monteith model in this region, pan evaporation coefficient (K p) is very important when using observed E p to predict ET 0. Under this circumstance, an empirical formula of K p was put forward for this region; (4) Crop coefficient (K c), an important index to reflect evapotranspiration, was also analyzed. Results show that mean annual values of ET 0 and ET c were 840 and 221 mm, respectively. On the daily bases, ET 0 and ET c were 2.3 and 0.6 mm/d, respectively. The annual tendency of ET 0 and ET c was very similar, but their amplitude was obviously different. The differences among ET 0 and ET c were mainly attributed to the different meteorological variables and leaf area index. The calculated K c was about 0.25 and showed little variation during the growing season, indicating that available water (e.g. precipitation and irrigation) of about 221 mm/a was required to keep the water balance in this region. The results provide an comprehensive analysis of evapotranspiration for an oasis-desert transition zone in the middle stream of Heihe River, which was seldom reported before.