Fire causes abrupt changes in vegetation properties
and modifies flux exchanges between land and atmosphere
at subseasonal to seasonal scales. Yet these shortterm
fire effects on vegetation dynamics and surface energy
balance have not been comprehensively investigated
in the fire-coupled vegetation model. This study applies
the SSiB4/TRIFFID-Fire (the Simplified Simple Biosphere
Model coupled with the Top-down Representation of Interactive
Foliage and Flora Including Dynamics with fire) model
to study the short-term fire impact in southern Africa. Specifically,
we aim to quantify how large impacts fire exerts on
surface energy through disturbances on vegetation dynamics,
how fire effects evolve during the fire season and the subsequent
rainy season, and how surface-darkening effects play a
role besides the vegetation change effects.
We find fire causes an annual average reduction in grass
cover by 4 %–8% for widespread areas between 5–20 S and
a tree cover reduction by 1% at the southern periphery of
tropical rainforests. The regional fire effects accumulate during
June–October and peak in November, the beginning of
the rainy season. After the fire season ends, the grass cover
quickly returns to unburned conditions, while the tree fraction
hardly recovers in one rainy season. The vegetation removal
by fire has reduced the leaf area index (LAI) and gross
primary productivity (GPP) by 3 %–5% and 5 %–7% annually.
The exposure of bare soil enhances surface albedo and
therefore decreases the absorption of shortwave radiation.
Annual mean sensible heat has dropped by 1.4Wm−2, while
the latent heat reduction is small (0.1Wm−2/ due to the evaporation. Surface temperature is increased by as much as
0.33K due to the decrease of sensible heat fluxes, and the
warming would be enhanced when the surface-darkening effect
is incorporated. Our results suggest that fire effects in
grass-dominant areas diminish within 1 year due to the high
resilience of grasses after fire. Yet fire effects in the periphery
of tropical forests are irreversible within one growing season
and can cause large-scale deforestation if accumulated for
hundreds of years.
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Reforestation and surface cooling in temperate zones: Mechanisms and implications
Land‐use/cover change (LUCC) is an important driver of environmental change, occurring at the same time as, and often interacting with, global climate change. Reforestation and deforestation have been critical aspects of LUCC over the past two centuries and are widely studied for their potential to perturb the global carbon cycle. More recently, there has been keen interest in understanding the extent to which reforestation affects terrestrial energy cycling and thus surface temperature directly by altering surface physical properties (e.g., albedo and emissivity) and land–atmosphere energy exchange. The impacts of reforestation on land surface temperature and their mechanisms are relatively well understood in tropical and boreal climates, but the effects of reforestation on warming and/or cooling in temperate zones are less certain. This study is designed to elucidate the biophysical mechanisms that link land cover and surface temperature in temperate ecosystems. To achieve this goal, we used data from six paired eddy‐covariance towers over co‐located forests and grasslands in the temperate eastern United States, where radiation components, latent and sensible heat fluxes, and meteorological conditions were measured. The results show that, at the annual time scale, the surface of the forests is 1–2°C cooler than grasslands, indicating a substantial cooling effect of reforestation. The enhanced latent and sensible heat fluxes of forests have an average cooling effect of −2.5°C, which offsets the net warming effect (+1.5°C) of albedo warming (+2.3°C) and emissivity cooling effect (−0.8°C) associated with surface properties. Additional daytime cooling over forests is driven by local feedbacks to incoming radiation. We further show that the forest cooling effect is most pronounced when land surface temperature is higher, often exceeding −5°C. Our results contribute important observational evidence that reforestation in the temperate zone offers opportunities for local climate mitigation and adaptation.
more » « less- NSF-PAR ID:
- 10453660
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 26
- Issue:
- 6
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 3384-3401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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