Abstract
The effect of vegetation on temperature is an emerging topic in the climate science community. Existing studies have mostly examined the effects of vegetation on daytime temperature (Tmax), whereas this study investigates the effects on nighttime temperature (Tmin). Ground measurements from 53 sites across northeastern China (NEC) from 1982 to 2006 show that early summer (June) Tmax and Tmin increased at mean rates of approximately 0.61 °C/10 year and 0.67 °C/10 year, respectively. Over the same period, the satellite-based Normalized Difference Vegetation Index (NDVI) decreased by approximately 0.10 (accounting for 18% of the climatological NDVI for 1982–1991). It is highlighted that a larger increase in Tmax (Tmin) co-occurred spatially with a larger (smaller) decrease in NDVI. Deriving from such spatial co-occurrences, we found that the spatial variability of changes in Tmax (i.e., ΔTmax) is negatively correlated with the spatial variability of changes in NDVI (i.e., ΔNDVI), while the spatial variability of changes in Tmin (i.e., ΔTmin) is positively correlated (r2 = 0.10; p < 0.05) with that of ΔNDVI. Similarly, we detected significant positive correlations between the spatial variability of ΔNDVI and the change in surface latent heat flux (r2 = 0.16; p < 0.01) and in surface air specific humidity (r2 = 0.28; p < 0.001). These findings on the spatial co-occurrences suggest that the vegetation growth intensifies the atmospheric water vapor through evapotranspiration, which enhances the atmospheric downward longwave radiation and strengthens the greenhouse warming effects at night. Thereby, the positive correlation between ΔNDVI and ΔTmin is better understood. These results indicate that vegetation growth may not only exert effects on daytime temperature but also exert warming effects on nighttime temperature by increasing atmospheric water vapor and thus intensifying the local greenhouse effect. This study presents new observation evidence of the effects of vegetation on local temperature.
Highlights
The terrestrial biosphere is a key regulator of climate [1,2]
The spatial distribution of the pixel-based changes shows that there was a widespread decrease in Normalized Difference Vegetation Index (NDVI) across the Northeast China Plain, which was predominantly covered by cropland
∆NDVI showed a pattern that was characterized by strong surface browning in the north and weak browning in the south
Summary
The terrestrial biosphere is a key regulator of climate [1,2]. Changes in vegetation may provide feedback to the climate via shifts in the surface energy balance, evapotranspiration, friction, and the resultant effects on surface temperature, precipitation, pressure, and wind. As indicated by the reviews by Pitman et al [4] and Mahmood et al [5], the biogeophysical effects of vegetation variation on the global climate may be limited, but the effects on the regional and local weather and climate are significant. Due to such knowledge, vegetation variations are being evaluated to understand past climate changes [6] and predict future climate at the regional scale [7]. The growth of vegetation leads to an increase in Et and, a decrease in sensible heat, which directly heats the bottom of the atmosphere
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