Sensitivity of isoprene emissions to drought over south-eastern Australia: Integrating models and satellite observations of soil moisture
Sensitivity of isoprene emissions to drought over south-eastern Australia: Integrating models and satellite observations of soil moisture
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异戊二烯排放对澳大利亚东南部干旱的敏感性：整合土壤湿度模型和卫星观测
DOI：
10.1016/j.atmosenv.2019.04.038
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发表时间：
2019
影响因子：
5
通讯作者：
Guenther, Alex B.
中科院分区：
文献类型：
--
作者：
Emmerson, Kathryn M.;Palmer, Paul I.;Thatcher, Marcus;Haverd, Vanessa;Guenther, Alex B.
澳大利亚东南部以干旱和半干旱气候为特点，近几十年来降雨量大规模减少。预测了未来较大的时空干旱条件。温带东南沿海地区的特点是茂密的桉树林。干旱条件对这些土著生态系统的功能产生了影响，并对沿着东海岸主要大都市地区上风处的活性气体排放产生了影响。在这里，我们重点关注干旱对异戊二烯排放的影响，异戊二烯是一种挥发性有机化合物，由一系列树木和灌木排放。先前的模型计算严重高估了异戊二烯混合比的观测值，这可能是由于高估了原生植被的排放系数，但也可能是由于干旱引起的异戊二烯排放减少。我们在CSIRO化学传输模型中开发了天然气和气溶胶排放模型（MEGAN）的实施，以包括使用土壤水分的干旱参数化。我们使用两种方法来测试这种参数化。首先，我们使用来自两个澳大利亚地表模型的土壤湿度场驱动MEGAN，实现夏季异戊二烯排放量减少24-52%。其次，我们使用一个简单的统计方法，从土壤水分和海洋盐度（SMOS）仪器的卫星观测模型土壤水分。这项工作是第一次应用SMOS对异戊二烯排放建模，提供了一个限制表层土壤水分扩展到全球范围。应用这些土壤水分方法，区域平均异戊二烯排放量减少38-58%，在夏季。使用这些结果，基础排放的误差可能在40%的范围内。将模拟的土壤湿度与使用4 m深度的根密度加权平均值进行的观测结果进行比较，显示出高达0.04 m3 m −3的微小差异。我们发现，在SMOS同化使用的陆面模型的选择有更大的影响异戊二烯排放量比调整无论是轻推强度或土壤水平的数量，这些卫星数据可能会影响。然而，当使用每小时或24小时土壤湿度输入数据来驱动排放计算时，只有3%的微小差异，这表明卫星数据的较低时间可用性不会降低模型质量。随着大气成分和地表特性的卫星观测的空间分辨率开始接近管制空气质量模型的分辨率，我们预计这些数据将进一步提高模型预测技能。
South-east Australia, characterized by arid and semi-arid climate, has experienced large-scale rainfall reductions in recent decades. Larger temporal and spatial drought conditions are predicted in future. The temperate south east coastal zone is characterized by dense forests of Eucalyptus. Drought conditions have implications for the functioning of these indigenous ecosystems, and for emissions of reactive gases that are upwind of major metropolitan regions along the eastern coast. Here, we focus on the impact of drought on the emission of isoprene, a volatile organic compound emitted by a range of trees and shrubs. Previous model calculations grossly overestimate observations of the isoprene mixing ratio, potentially due to overestimated emission factors for native vegetation, but could also be due to drought-induced isoprene emission reductions. We develop the implementation of the Model of Emissions of Gases and Aerosols from Nature (MEGAN) within the CSIRO Chemical Transport Model to include a parameterization of drought using soil moisture. We test this parameterization using two approaches. First, we drive MEGAN using soil moisture fields from two Australian land surface models achieving reductions in isoprene emissions of 24–52% during summer. Second, we use a simple statistical approach to nudge model soil moisture towards satellite observations from the Soil Moisture and Ocean Salinity (SMOS) instrument. This work is the first application of SMOS towards isoprene emission modelling, providing a constraint on surface soil moisture which extends to global scales. Applying these soil moisture approaches, domain average isoprene emissions reduce by 38–58% in summer. Using these results, errors in basal emissions are likely in the region of 40%. Comparison of modelled soil moisture to observations using root density weighted averages across depths of 4 m showed minor differences of up to 0.04 m3m−3. We find that the choice of land surface model used in the SMOS assimilations has a greater impact on isoprene emissions than adjusting either the nudging strength or the number of soil levels these satellite data may influence. However there are only small differences of 3% when using hourly or 24-hourly soil moisture input data to drive the emission calculations, suggesting that the lower temporal availability of satellite data does not reduce model quality. As the spatial resolution of satellite observations of atmospheric composition and land surface properties begin to approach the resolution of regulatory air quality models, we anticipate that these data will improve model predictive skills further.
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