Clod and Arid Regions Environmental and Engineering Research Institute, Key Laboratory of Land Surface Process and Climate Change in Cold & Arid Regions, Chinese Academy of Sciences, Lanzhou 730000, China.
Clod and Arid Regions Environmental and Engineering Research Institute, Key Laboratory of Land Surface Process and Climate Change in Cold & Arid Regions, Chinese Academy of Sciences, Lanzhou 730000, China; College of Environmental Science & Engineering, Nankai University, Tianjin 300071, China.
Sci Total Environ. 2016 Nov 1;569-570:404-415. doi: 10.1016/j.scitotenv.2016.06.143. Epub 2016 Jun 25.
Since 1999 Chinese government has made great effort to reforest the south and north mountains surrounding urban Lanzhou - a city located in a river valley, Northwestern China. Until 2009 obvious land use change occurred, with 69.2% of the reforested area been changed from grasslands, croplands, barren or sparsely vegetated land to closed shrublands and 20.6% from closed shrublands, grasslands, and croplands to forests. Reforestation changes land-surface properties, with possible impact on the evolution of atmospheric variables. To understand to what extent the local meteorology and environment could be affected by reforestation in winter, and through what processes, two sets of simulations were conducted using the Weather Research and Forecasting model (WRF) and the FLEXible PARTicle (FLEXPART) dispersion model for a control case with high-resolution remotely sensed land cover data for 2009 and a scenario assuming no reforestation since 1999. Results suggested that the changes in albedo, surface exchange coefficient and surface soil heat conductivity related to reforestation led to the changes in surface net radiation and surface energy partitioning, which in turn affected the meteorological fields and enhanced the mountain-valley wind circulation. Replacement of shrublands and grassland with forest in the south mountain through reforestation play a dominant role in the enhancement of mountain-valley wind circulation. Reforestation increased the amount of air exchanged between the valley and the outside during the day, with the largest hourly increase of 10% on calm weather days and a monthly mean hourly increase of 2% for the study period (Dec. 2009). Reforestation affected the spatial distribution of pollutants and slightly improved the urban air quality, especially in the eastern valley. Results from this study provide useful information for future urban air quality management and reforestation plan, and some experience for cities with similar situations in the world.
自 1999 年以来，中国政府一直致力于在中国西北河谷城市兰州的南北山区进行造林。到 2009 年，明显的土地利用变化发生了，69.2%的造林区从草地、耕地、荒地或稀疏植被变为封闭灌丛，20.6%的造林区从封闭灌丛、草地和耕地变为森林。造林改变了地表性质，可能对大气变量的演变产生影响。为了了解造林在冬季对当地气象和环境的影响程度以及通过什么过程产生影响，利用天气研究和预报模型（WRF）和灵活颗粒（FLEXPART）扩散模型进行了两组模拟，一组是使用高分辨率遥感土地覆盖数据的 2009 年控制案例，另一组是假设自 1999 年以来没有进行造林的情景。结果表明，造林引起的反照率、地表交换系数和地表土壤热导率的变化导致地表净辐射和地表能量分配的变化，进而影响气象场并增强山区-山谷风环流。通过造林，南山的灌丛和草地被森林取代，在增强山区-山谷风环流方面发挥了主导作用。造林增加了山谷与外部之间的空气交换量，在平静天气日最大每小时增加 10%，研究期间（2009 年 12 月）每月平均每小时增加 2%。造林影响了污染物的空间分布，并略微改善了城市空气质量，特别是在东部山谷。本研究结果为未来城市空气质量管理和造林计划提供了有用的信息，并为世界上类似情况的城市提供了一些经验。
