Radiation budget changes with dry forest clearing in temperate Argentina

Abstract

Land cover changes may affect climate and the energy balance of the Earth through their influence on the greenhouse gas composition of the atmosphere (biogeochemical effects) but also through shifts in the physical properties of the land surface (biophysical effects). We explored how the radiation budget changes following the replacement of temperate dry forests by crops in central semiarid Argentina and quantified the biophysical radiative forcing of this transformation. For this purpose, we computed the albedo and surface temperature for a 7-year period (2003-2009) from MODIS imagery at 70 paired sites occupied by native forests and crops and calculated the radiation budget at the tropopause and surface levels using a columnar radiation model parameterized with satellite data. Mean annual black-sky albedo and diurnal surface temperature were 50% and 2.5 °C higher in croplands than in dry forests. These contrasts increased the outgoing shortwave energy flux at the top of the atmosphere in croplands by a quarter (58.4 vs. 45.9 W m(-2) ) which, together with a slight increase in the outgoing longwave flux, yielded a net cooling of -14 W m(-2) . This biophysical cooling effect would be equivalent to a reduction in atmospheric CO2 of 22 Mg C ha(-1) , which involves approximately a quarter to a half of the typical carbon emissions that accompany deforestation in these ecosystems. We showed that the replacement of dry forests by crops in central Argentina has strong biophysical effects on the energy budget which could counterbalance the biogeochemical effects of deforestation. Underestimating or ignoring these biophysical consequences of land-use changes on climate will certainly curtail the effectiveness of many warming mitigation actions, particularly in semiarid regions where high radiation load and smaller active carbon pools would increase the relative importance of biophysical forcing.

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

“…In temperate Argentina, Houspanossian et al (2013) found that the replacement of dry forests by crops resulted in an increase of albedo but still forests exhibited cooler canopies than croplands. The cooler canopies were a result of a higher aerodynamic conductance that enhanced the capacity of tree canopies to dissipate heat into the atmosphere and to both latent and sensible heat fluxes operating simultaneously to cool forest canopies.…”

Uso de la tierra y ambiente local de descomposición en el Chaco Semiárido de Córdoba, Argentina

“…Existen evidencias de que los cambios en la cobertura de la vegetación pueden modificar las condiciones climáticas a escala local, regional y global (Adams 2007;Lee et al 2011;Anderson-Teixeira et al 2012;Houspanossian et al 2013;Flerchinger et al 2015). A su vez, pueden tener efectos sobre la interfaz broza-suelo donde se produce la descomposición (Eviner and Chapin 2003;Yates et al 2000;Schiling et al 2016 o similares).…”

“…A su vez, pueden tener efectos sobre la interfaz broza-suelo donde se produce la descomposición (Eviner and Chapin 2003;Yates et al 2000;Schiling et al 2016 o similares). En las configuraciones vegetales analizadas durante los años estudiados (2009)(2010)(2011), la mayor temperatura del aire observada en el arbustal mixto cerrado y los bosques puede deberse a que el menor albedo que poseerían (Lee et al 2011;AndersonTeixeira 2012) no se vea compensado por su mayor rugosidad (y su mayor disipación de calor latente), como podría esperarse en base a estudios previos (Houspanossian et al 2013). A su vez, una mayor temperatura podría deberse a que en arbustales y bosques existe una mayor superficie oscura de troncos, ramas y broza sobre el suelo, que podría retener calor incluso durante la noche, cuando el efecto de la rugosidad en disipar calor sería más importante (Eviner and Chapin 2003;Adams 2007).…”

Forest summer albedo is sensitive to species and thinning: how should we account for this in Earth system models?

“…The complete cutting of trees, however, removes the entire canopy and thus presumably would have the opposite effect. Indeed, a negative radiative forcing of up to −18 Wm −2 in summer was measured from clear-cutting in the temperate zone (Houspanossian et al, 2013).…”