Soil moisture and vegetation controls on evapotranspiration in a heterogeneous Mediterranean ecosystem on Sardinia, Italy
Soil moisture and vegetation controls on evapotranspiration in a heterogeneous Mediterranean ecosystem on Sardinia, Italy
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DOI：
10.1029/2005wr004693
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发表时间：
2006-08-11
影响因子：
5.4
通讯作者：
Katul, Gaby
中科院分区：
文献类型：
--
作者：
Detto, Matteo;Montaldo, Nicola;Katul, Gaby
[1]在存在土地覆盖异质性的情况下，蒸散(ET)的微气象测量可能难以解释和用于验证模型计算。2003年4月至2004年7月，地表通量、土壤湿度(Theta)和地表温度(T-S)数据由位于奥罗里(撒丁岛)试验场(被木本植物、草地和裸露土壤覆盖)的涡旋相关塔收集。获取了两张Quickbird高分辨率图像(2003年夏季和2004年春季)，以描绘对比鲜明的土地覆盖成分。提出了一种利用TS观测、二维足迹模型和Quickbird图像估算异质生态系统中的ET作为能量平衡的残余项的方法。成功地实现了该方法的两种变形：一种是建议的两源随机模型(2SR)，该模型分别处理每个地表覆盖组分的热源，但计算总体换热系数是空间均匀的；另一种是普通的两源瓦片模型。对于2SR，估算了两种裸露土壤-木本植被和草-木本植被复合表面界面迁移系数与粗糙度雷诺数之间的新关系。还估计了每个土地覆盖成分的ET与Theta的关系，表明木本植被对长期干旱具有很强的耐受性，即使在最干燥的条件下，蒸腾速率也接近潜在的速率。相反，草对theta缺乏的耐受性要差得多，雨季后从草到裸地的转变对ET产生了重大影响。
[ 1] Micrometeorological measurements of evapotranspiration ( ET) can be difficult to interpret and use for validating model calculations in the presence of land cover heterogeneity. Land surface fluxes, soil moisture (theta), and surface temperatures (T-s) data were collected by an eddy correlation-based tower located at the Orroli ( Sardinia) experimental field ( covered by woody vegetation, grass, and bare soil) from April 2003 to July 2004. Two Quickbird high-resolution images ( summer 2003 and spring 2004) were acquired for depicting the contrasting land cover components. Aprocedure is presented for estimating ET in heterogeneous ecosystems as the residual term of the energy balance using Ts observations, a two-dimensional footprint model, and the Quickbird images. Two variations on the procedure are successfully implemented: a proposed two-source random model (2SR), which treats the heat sources of each land cover component separately but computes the bulk heat transfer coefficient as spatially homogeneous, and a common two-source tile model. For 2SR, new relationships between the interfacial transfer coefficient and the roughness Reynolds number are estimated for the two bare soil - woody vegetation and grass - woody vegetation composite surfaces. The ET versus theta relationships for each land cover component were also estimated, showing that that the woody vegetation has a strong tolerance to long droughts, transpiring at rates close to potential for even the driest conditions. Instead, the grass is much less tolerant to theta deficits, and the switch from grass to bare soil following the rainy season had a significant impact on ET.