Local boundary-layer development over burnt and unburnt tropical savanna: an observational study

Abstract

Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo, increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site a low to moderate intensity fire, ranging between 1,000 and 3,500 kW m −1 , initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface, scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2 • C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating and precipitation patterns that may affect larger-scale processes such as the Australian monsoon.

Analysis of the Relationship between Land Surface Temperature and Wildfire Severity in a Series of Landsat Images

“…This is similar to the results reported by the previous research [5,6,8], although the range and the size of the differences between severity categories of the same date is much larger than that detected in the earlier studies. This is probably due to the different response of the analyzed vegetation: much more homogeneous in this study (predominantly conifer forests) than analyzed in the study by Veraverbeke et al [8] (shrublands, olive groves, coniferous and deciduous forests).…”

“…The decrease of aboveground green biomass in the burned zones [12], especially in those of higher severity, and the appearance of lower emissivity coverage (ash, char and mineral soils) lead to a large increase in the LST. Elevated LST after fire events is mentioned by several authors (among others Lambin et al [7]; Montes-Helu et al [5]; Wendt et al [6]). Veraverbeke et al [8] studied this increase using MODIS imagery following the major Peloponnese fire in 2007.…”

“…In the context of wildfire studies, fire-induced environmental changes cause variations in the spatial distribution of LST, mainly due to a decrease in transpiration and an increase in the Bowen ratio (β = sensible heating/latent heating) [4]. The higher post-fire LST of the burned areas was observed in field data [5,6] and remotely-sensed images [7,8]. Moreover, according to Beringer et al [9], there is a relationship between fire intensity and an increase in the Bowen ratio, as far as fire intensity determines the likely impact on energy and carbon fluxes.…”

On the meteorological and hydrological mechanisms resulting in the 2003 post-fire flood event in Alpine Shire, Victoria

“…Based on the interviews with shire residents and photos during and after the event, it was apparent that the fire was of great intensity. The chosen values for the relevant model parameters reflect this observation and were based on previous work on modelling fire scars (Görgen et al 2006;Wendt et al 2007.) The albedo was reduced from 0.20 to 0.08, the roughness length from 2.65 m to 0.10 m, and the soil moisture for the uppermost 10 cm layer was initialised at 0. .…”

SPECIAL—Savanna Patterns of Energy and Carbon Integrated across the Landscape

“…1). Alterations to biophysical processes within ecosystems can, in turn, influence boundary layer development (Wendt et al 2007) and can also cause mesoscale circulations as a result of vegetation discontinuities (Lee and Kimura 2001;Raddatz 2007). Regional differences in vegetation will cause large-scale albedo anomalies that have been shown to change regional atmospheric circulation patterns (Charney et al 1975;Chase et al 1996).…”