Local cooling and warming effects of forests based on satellite observations

Abstract

The biophysical effects of forests on climate have been extensively studied with climate models. However, models cannot accurately reproduce local climate effects due to their coarse spatial resolution and uncertainties, and field observations are valuable but often insufficient due to their limited coverage. Here we present new evidence acquired from global satellite data to analyse the biophysical effects of forests on local climate. Results show that tropical forests have a strong cooling effect throughout the year; temperate forests show moderate cooling in summer and moderate warming in winter with net cooling annually; and boreal forests have strong warming in winter and moderate cooling in summer with net warming annually. The spatiotemporal cooling or warming effects are mainly driven by the two competing biophysical effects, evapotranspiration and albedo, which in turn are strongly influenced by rainfall and snow. Implications of our satellite-based study could be useful for informing local forestry policies.

Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia

“…The ETs were significant, highlighting that despite their higher albedo, all land cover types had higher LSTs than forests related to lower ET rates than forests. In contrast, forests that absorb more solar radiation because of the lower albedo have lower LST because of the higher ET they exhibit, hereby identifying evaporative cooling as the main determinant of regulating the surface temperature of all vegetation cover types (Li et al, 2015). Both observational and modeling studies carried out in other geographic regions and with other trajectories support our observations.…”

“…Similar effects were also observed for other South American biomes (Salazar et al, 2016). In a global analysis, Li et al (2015) showed that the cooling of forests is moderate at midlatitudes but northern boreal forests are warmer, an indication that the effect of land cover change on LST varies with the location of the land cover change (Longobardi et al, 2016). Similar studies on the Indonesian islands are lacking but surface temperature increases are expected as an effect of oil palm and cash crop land expansion in the recent decades.…”

“…In a global analysis Li et al (2015) showed that tropical forests generally have a low albedo, but still the net energy gain caused by solar energy absorption is offset by a greater latent heat loss via higher ET and that in the tropical forests the high ET cooling completely offsets the albedo warming. For China, this cooling effect was also shown by Peng et al (2014), who compared LST, albedo and ET of plantation forests, grassland and cropland with forests.…”

“…The average effect of land transformation, i.e. the change from forest to another non-forest land cover type, on the surface temperature was evaluated as (see Li et al, 2015) LST = LST non−forest − LST forest .…”

Local Effects of Forests on Temperatures across Europe

“…There are two kinds of observations, that are widely used to explore the effects of forests on temperature: satellite and in-situ data [7,14,[17][18][19][20]. Some studies used satellite observations found that afforestation in China cooled daytime temperatures and warmed the nocturnal temperatures [18,20].…”