生长季植被覆盖变化对局地气象要素的可能影响

Possible Impacts of Vegetation Cover on Local Meteorological Factors in Growing Season

植被覆盖变化对地表气象要素存在反馈作用,但在不同时空尺度上反馈关系及其表现强度存在差异。作者利用地面观测资料和归一化植被指数(NDVI)分析了15天尺度上植被覆盖变化对气象要素的影响。结果表明,我国北方农牧交错带生长季植被覆盖变化可能对同期、后期地表气象要素存在一定影响。当植被指数偏高时,地表平均温度、最高温度、最低温度和小雨频次偏低,而平均相对湿度和最小相对湿度偏高,影响持续约为1～2周。地表温度和小雨频次的变化与地表热通量的变化有关,当植被指数偏高时,地表潜热所占比例偏高,而地表感热所占比例偏低,导致地表温度偏低;地表感热偏低伴随偏弱的上升运动,不利于降水,故小雨频次偏低。地表温度偏低引起饱和比湿偏低,加之植被蒸腾量较大引起比湿偏高,故相对湿度偏高。此外,从长期变化来看NDVI与地表温度和小雨频次的相关不明显,故地表温度和小雨频次的长期变化可能更多是受大尺度气候变化的影响。

Vegetation can feedback on meteorological factors, both directly on the energy budget through surface albedo and exchanges of heat, water, and momentum and indirectly on the biogeochemieal process. The relationship and amplitude of the feedback of vegetation, however, varies with different spatial and temporal scales. In this study, the authors apply the observational datasets and Normalized Difference Vegetation Index （NDVI） datasets from 1982 to 2003 to depict the association of the NDVI over the agro-pasture zone of China with meteorological factors on the 15 days timescale. The results show that the vegetation change in spring over the north part of China may significantly impact the simultaneous and subsequent meteorological factors. When the NDVI is abnormally higher, the mean temperature, maximum temperature, minimum temperature and light rainfall frequency are abnormally lower, but the mean relative humid and minimum relative humid are abnormally higher. The possible impacts of vegetation on meteorological factors may sustain 1--2 weeks. The change of temperature and light rainfall frequency is related with the change of surface heat fluxes. When NDVI is abnormally higher, the surface latent heat is abnormally higher and sensible heat is abnormally lower, which causes the surface temperature lower. The decreased surfaces sensible heat is accompanied by weaken ascending flows, which do not provide help for the formation of light rainfall and subsequently makes the light rainfall frequency decrease. Also the lower surface temperature results in the drop of the saturation mixing ratio. Due to that the added transpiration tends to increase the mixing ratio, the relative humid ratio rises. In addition, the relationship of NDVI with temperature and light rainfall frequency is not significant on long timescales, so the long-term change of temperature and light rainfall frequency may be more related with other climate changes on large scales than vegetation.