基于Shuttleworth-Wallace模型的科尔沁沙地流动半流动沙丘蒸散发模拟

陆面蒸散发在气候调节和维持区域水量平衡中起关键作用.量化蒸散发及其各组分项,对深刻揭示干旱半干旱地区的生态水文过程具有重要意义.本研究基于科尔沁沙地流动半流动沙丘2017年生长季气象监测系统的原位监测数据,利用Shuttleworth-Wallace(S-W)模型对沙丘蒸散发进行模拟,在此基础上,对蒸散各组分进行拆分,并利用涡度相关对模拟蒸散发值进行验证.结果表明: 整个生长季模型模拟蒸散发值为308 mm,涡度相关实测值为296 mm,偏差较小,证明S-W模型适用于该地区的蒸散发模拟.蒸散发整体呈生长旺盛期>生长后期>生长初期,分别为192、71和45 mm,分别占总量的62.3%、23.1%和14.6%.日尺度上模型模拟值与实测蒸散发值一致性较高,模型模拟精度大体表现为: 晴天>阴天>雨天,且阴雨天模型模拟值较涡度相关实测值偏低.经拆分,土壤蒸发和植被蒸腾分别为176和132 mm,分别占总量的57.1%和42.9%,表明沙地水分利用效率较低.持续干旱和降水后,蒸散发规律明显不同,且土壤蒸发对降水的敏感性强于植被蒸腾.

Simulation of evapotranspiration for the mobile and semi-mobile dunes in the Horqin Sandy Land using the Shuttleworth-Wallace model

Terrestrial evapotranspiration (ET) plays a crucial role in climate regulation and the maintenance of regional water balance. Quantitative estimation of ET and its partitioning are important for revealing the eco-hydrological processes in arid and semi-arid areas. Using the in situ data sampled by the meteorological monitoring system, the Shuttleworth-Wallace (S-W) model was applied to simulate and partition ET in the mobile and semi-mobile dunes of the Horqin sandy land during the growing season in 2017. The eddy covariance system was used to verify the simulated ET. The results were as follows: the simulated ET (308 mm) was very close to the eddy covariance observed ET (296 mm) during the whole growing season, indicating the applicability of the S-W model for ET estimation in this area. The ET rate at the vigorous growth stage (192 mm) was larger than those at the late and early growth stages (71 and 45 mm, respectively) which accounted for 62.3%, 23.1%, and 14.6% of the total, respectively. The simulated ET was close to the eddy covariance observed ET at the daily time-scale. The simulation performance of the S-W model for clear days was better than for cloudy or rainy days. The simulated ET rate was always smaller than the eddy covariance observed ET in the cloudy or rainy days. According to the model, the evaporation (E) from soil was 176 mm and the transpiration (T) from plants was 132 mm, accounting for 57.1% and 42.9% of the ET, respectively, suggesting that water use efficiency of the sand dune was low. The characteristics of ET varied substantially under the sustained drought and precipitation events. Compared to T from plants, E from soil was more sensitive to precipitation.