长三角地区农业与自然植被镶嵌体的变化对近地面气象场的影响评估

Impact assessment of changes in agricultural and natural vegetation mosaics on near-surface meteorological fields in the Yangtze River Delta

利用一个中尺度数值模式WRF3.8/Noah/UCM,对长三角地区近30 a来灌溉水田显著减少,农业与自然植被镶嵌体(以下简称镶嵌体)显著增加这一现象引起的气候效应进行了5 a(2008—2012年)高分辨数值模拟。试验采用了ChinaLC土地覆盖资料,利用MODIS反照率和叶面积指数产品分别验证了ChinaLC在镶嵌体和水田之间的分类可靠性。根据研究区内台站观测资料评估了ChinaLC和WRF模式自带的USGS资料模拟结果,进一步证明土地覆盖资料ChinaLC的分类准确性,有助于提高模式的模拟性能。通过对长三角地区镶嵌体面积变化的对比试验进行分析,结果表明:区域内由灌溉水田转变为镶嵌体后,不仅会使非城市区气象条件改变,同时也会影响临近的城市区,由于非城市区增温幅度大于城市区,会导致城郊温差减弱;镶嵌体增加导致江苏西南部、浙江北部气温上升0.1～0.3℃,风速减弱0.1～0.3 m·s^(-1),比湿降低0.05～0.15 g·kg^(-1),边界层高度上升40 m。在镶嵌体显著增加的南京北部—滁州以及江苏西南部一带降水减少,南京北部—滁州地区月平均降水减少了0.6 mm·d^(-1),马鞍山—溧水降水减少了0.2 mm·d^(-1)。

This study uses a mesoscale numerical model WRF3.8/Noah/UCM,to conduct a 5-year(2008-2012)high resolution numerical simulation for the climate effect caused by the phenomenon of obvious decrease of irrigated paddy fields and obvious increase of agricultural and natural vegetation mosaics(hereinafter referred to as mosaics)in the Yangtze River Delta region in the past 30 years.First,ChinaLC land cover data was written into the WRF model.The classification reliability of ChinaLC between mosaics and paddy fields was verified by MODIS albedo and leaf area index products respectively.According to the station observation data,the built-in USGS data simulation results of ChinaLC and WRF models were evaluated.After analysis,the ChinaLC has been proved to have good classification accuracy and to be conducive to improving the simulation performance of the model.The results of an analysis of the contrast experiment of the Yangtze River Delta region show:because the mosaics areas took place of the paddy fields,not only the weather condition of non-urban areas changed,but also that of the urban areas was affected,and since the growth rate in non-urban areas was larger than that in urban areas,the temperature difference between urban and non-urban areas weakened.Due to the increase of mosaics,temperature increased 0.1-0.3℃in the southwest of Jiangsu and north of Zhejiang Province,the wind speed decreased by 0.1-0.3 m·s^-1,the specific humidity decreased by 0.05-0.15 g·kg^-1 and the planetary boundary layer height increased by 40 m.The precipitation decreased in Northern Nanjing-Chuzhou and southwestern Jiangsu Province,where the mosaic significantly increased.The average monthly precipitation in Northern Nanjing-Chuzhou decreased by 0.6 mm·d^-1,and that in Ma'anshan-Lishui decreased by 0.2 mm·d^-1.