The partitioning of evapotranspiration into transpiration, soil evaporation, and canopy evaporation in a GCM: Impacts on land-atmosphere interaction
The partitioning of evapotranspiration into transpiration, soil evaporation, and canopy evaporation in a GCM: Impacts on land-atmosphere interaction
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DOI：
10.1175/jhm596.1
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发表时间：
2007-08-01
影响因子：
3.8
通讯作者：
Bonan, Gordon B.
中科院分区：
文献类型：
--
作者：
Lawrence, David M.;Thornton, Peter E.;Bonan, Gordon B.
虽然蒸散发（ET）在全球范围内被划分为蒸腾、土壤蒸发量和冠层蒸发量尚不清楚，但目前大多数陆地表面方案和少量观测资料表明，蒸腾是全球尺度上的主要组分，其次是土壤蒸发量和冠层蒸发量。然而，社区土地模型第3版（CLM3）并没有反映出这种整体的蒸散发分配观点，土壤蒸发和冠层蒸发远远超过蒸腾。CLM3中这种不切实际的蒸散发分配的一个后果是，光合作用（通过气孔导度与蒸腾作用相关）在全球范围内被严重低估。本文描述了对CLM3植被和土壤水文参数化的一些修改，这些修改改善了CLM3的ET分配，减少了明显的干土偏差。这些修改减少了冠层的截流和蒸发，减少了土壤对蒸腾的水分胁迫，通过更现实的冠层整合方案增加了蒸腾，减少了冠层内土壤蒸发，消除了土壤水分的侧向排水，增加了水分向土壤的入渗，增加了土壤水分的垂直再分配。蒸散发的分配得到改善，蒸腾（占全球蒸散发的13%-41%）和光合作用（65-148 Pg C /年（-1））显著增加。土壤更湿润，表现出更明显的土壤水分年循环和更大的季节间土壤水分储存，这允许植物在旱季维持蒸腾作用。改进的ET分配对陆地-大气相互作用的广泛影响是多种多样的。蒸腾作用的增强和冠层蒸发量的减少使蒸散发对降雨事件的响应扩大，并使降水分布向更频繁的中小型降雨事件转变。土壤水分记忆时间尺度在较深的土层上尤其减小。地下土壤湿度对降水的影响略大。这些结果表明，蒸散发的分配是陆地表面方案的一个重要责任，随着gcm演变为包含地球碳和水文循环的更复杂处理，这一责任将获得相关性。
Although the global partitioning of evapotranspiration ( ET) into transpiration, soil evaporation, and canopy evaporation is not well known, most current land surface schemes and the few available observations indicate that transpiration is the dominant component on the global scale, followed by soil evaporation and canopy evaporation. The Community Land Model version 3 (CLM3), however, does not reflect this global view of ET partitioning, with soil evaporation and canopy evaporation far outweighing transpiration. One consequence of this unrealistic ET partitioning in CLM3 is that photosynthesis, which is linked to transpiration through stomatal conductance, is significantly underestimated on a global basis. A number of modifications to CLM3 vegetation and soil hydrology parameterizations are described that improve ET partitioning and reduce an apparent dry soil bias in CLM3. The modifications reduce canopy interception and evaporation, reduce soil moisture stress on transpiration, increase transpiration through a more realistic canopy integration scheme, reduce within-canopy soil evaporation, eliminate lateral drainage of soil water, increase infiltration of water into the soil, and increase the vertical redistribution of soil water. The partitioning of ET is improved, with notable increases seen in transpiration (13%-41% of global ET) and photosynthesis (65-148 Pg C yr(-1)). Soils are wetter and exhibit a far more distinct soil moisture annual cycle and greater interseasonal soil water storage, which permits plants to sustain transpiration through the dry season.The broader influences of improved ET partitioning on land-atmosphere interaction are diverse. Stronger transpiration and reduced canopy evaporation yield an extended ET response to rain events and a shift in the precipitation distribution toward more frequent small- to medium-size rain events. Soil moisture memory time scales decrease particularly at deeper soil levels. Subsurface soil moisture exerts a slightly greater influence on precipitation. These results indicate that partitioning of ET is an important responsibility for land surface schemes, a responsibility that will gain in relevance as GCMs evolve to incorporate ever more complex treatments of the earth's carbon and hydrologic cycles.