Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S.A.S Nagar, Manauli PO, Punjab 140306, India.
National Center for Atmospheric Research, Boulder, CO, USA.
Sci Total Environ. 2021 Jan 10;751:141728. doi: 10.1016/j.scitotenv.2020.141728. Epub 2020 Aug 19.
Trees significantly impact land-atmosphere feedbacks through evapotranspiration, photosynthesis and isoprene emissions. These processes influence the local microclimate, air quality and can mitigate temperature extremes and sequester carbon dioxide. Despite such importance, currently only 5 out of 15 atmospheric chemistry climate models even partially account for the presence of cropland trees. We first show that the tree cover over intensely farmed regions in Asia, Australia and South America is significantly underestimated (e.g. only 1-3% tree cover over north-India) in the Model of Emissions of Gases and Aerosol from Nature (MEGAN) and absent in Noah land-surface module of the Weather Research and Forecasting (WRF-Chem) Model. By including the actual tree cover (~10%) over the north-west Indo Gangetic Plain in the Noah land-surface module of the WRF-Chem and the MEGAN module, during the rice growing monsoon season in August, we find that the latent heat flux alone increases by 100%-300% while sensible heat flux reduces by 50%-100%, leading to a reduction in daytime boundary layer height by 200-400 m. This greatly improves agreement between the modelled and measured temperature, boundary layer height and surface ozone, which were earlier overestimated and isoprene and its oxidation products which were earlier underestimated. Mitigating peak daytime temperatures and ozone improves rice production by 10 to 20%. Our findings from north west Indo-Gangetic Plain establish that such plantations mitigate heat stress, and have beneficial effects on crop yields while also sequestering carbon. Expanding agroforestry practices to 50% of the cropland area could result in up to 40% yield gain regionally. Implementing such strategies globally could increase crop production and sequester 0.3-30 GtC per year, and therefore future climate mitigation and food security efforts should consider stakeholder participation for increased cropland agroforestry in view of its beneficial effects.
树木通过蒸腾作用、光合作用和异戊二烯排放对陆地-大气反馈产生重大影响。这些过程影响当地小气候、空气质量，并能缓解极端温度和固碳。尽管如此重要，但目前只有 15 个大气化学气候模型中的 5 个模型部分考虑了农田树木的存在。我们首先表明，亚洲、澳大利亚和南美洲高强度农业地区的树木覆盖率在大气排放源清单模型（MEGAN）中被严重低估（例如，印度北部的树木覆盖率仅为 1-3%），并且在天气研究与预报（WRF-Chem）模型的 Noah 陆面模块中缺失。通过在 WRF-Chem 的 Noah 陆面模块和 MEGAN 模块中纳入印度西北部恒河平原的实际树木覆盖率（约 10%），在 8 月水稻生长的季风季节，我们发现仅潜热通量就增加了 100%-300%，而感热通量减少了 50%-100%，导致白天边界层高度降低了 200-400 米。这极大地改善了模型和测量温度、边界层高度和地表臭氧之间的一致性，此前这些数值被高估，而异戊二烯及其氧化产物则被低估。缓解白天高温和臭氧峰值可使水稻产量提高 10%至 20%。我们在印度西北部恒河平原的研究结果表明，这种人工林可以减轻热应激，对作物产量有有益影响，同时还可以固碳。将农林业实践扩大到 50%的农田面积，可使该地区的产量提高 40%。在全球范围内实施这种策略可以增加作物产量，每年固碳 0.3-30 亿吨，因此，未来的气候缓解和粮食安全工作应考虑到利益相关者的参与，增加农田农林业，以其产生的有益影响。
