Abstract
Forests affect local climate through biophysical processes in terrestrial ecosystems. Due to the spatial and temporal heterogeneity of ecosystems in Europe, climate responses to forests vary considerably with diverse geographic and seasonal patterns. Few studies have used an empirical analysis to examine the effect of forests on temperature and the role of the background climate in Europe. In this study, we aimed to quantitatively determine the effects of forest on temperature in different seasons with MODIS (MODerate-resolution Imaging Spectroradiometer) land surface temperature (LST) data and in situ air temperature measurements. First, we compared the differences in LSTs between forests and nearby open land. Then, we paired 48 flux sites with nearby weather stations to quantify the effects of forests on surface air temperature. Finally, we explored the role of background temperatures on the above forests effects. The results showed that (1) forest in Europe generally increased LST and air temperature in northeastern Europe and decreased LST and air temperature in other areas; (2) the daytime cooling effect was dominate and produced a net cooling effect from forests in the warm season. In the cold season, daytime and nighttime warming effects drove the net effect of forests; (3) the effects of forests on temperatures were mainly negatively correlated with the background temperatures in Europe. Under extreme climate conditions, the cooling effect of forests will be stronger during heatwaves or weaker during cold spring seasons; (4) the background temperature affects the spatiotemporal distribution of differences in albedo and evapotranspiration (forest minus open land), which determines the spatial, seasonal and interannual effects of forests on temperature. The extrapolation of the results could contribute not only to model validation and development but also to appropriate land use policies for future decades under the background of global warming.
Highlights
Forests cover more than ~42 million km2 in the Northern Hemisphere (~30% of the land surface), and affects local climate mainly through biophysical processes [1,2,3,4]
Throughout this work, we analyzed the effects of forests on land surface temperature (LST) and air temperature in Europe using remote sensing data and in situ measurements to reveal the geographic and seasonal patterns of this effect
Our results show that (1) forests generally cool the LST and air temperature in Europe, and the cooling effect varies in space and decreases with increases in latitude and longitude, which causes a switch to a warming effect in northeastern Europe; (2) daytime cooling dominates the effect of forests in the warm seasons
Summary
Forests cover more than ~42 million km in the Northern Hemisphere (~30% of the land surface), and affects local climate mainly through biophysical processes [1,2,3,4]. The biophysical processes (e.g., albedo, evapotranspiration rate (ET) and surface roughness) all have effects on surface energy fluxes, which causes the effects of forests on local climates to be complicated [5]. Forests tend to cool the local temperature with a high latent heat flux. A comparison of these biophysical processes between forests and open lands can help us determine the effects of forests on local temperatures, a topic which has been analyzed in previous studies [9,10,11,12,13,14]
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