Publication Date:
2015-02-21
Description:
We compared the capacity of woody versus grassy vegetation covers to buffer high temperatures during heat waves by partitioning turbulent heat between latent ( λΕ ) and sensible ( H ) fluxes, and quantifying advection using the Priestley-Taylor coefficient (α), for a16-year old grassland and an adjoining 6-year old plantation. We found that because λE dominated (〉65%) the turbulent flux in the plantation, and was at least twice as large as on the grassland ( λE 〈35% of the turbulent flux) during heat waves, the ambient temperature over the plantation was up to 5 °C lower in the afternoon, and averaged 1.2 °C for the whole day, compared with the grassland. Both vegetation covers emitted significant amounts of H when soil-water availability was limited, and also in winter when canopy was mostly inactive because of dormancy in the grassland and mutual shading in the plantation due to low solar angle; during the winter, advection of additional energy from surrounding vegetation suppressed λE and reduced α to 〈1.0 in both vegetation covers. Advection enhanced λE during periods of frequent rainfalls in summer with mean α rising to 2.6 in the grassland and 3.4 in the plantation. Consistently low λΕ but high H made the grassland a source rather than a sink for advective energy, while the plantation was the opposite. The broadleaved evergreen woody vegetation consistently maintained a larger λΕ than the grassland in this mid-latitude environment, contrary to the smaller λΕ observed over mostly coniferous forests at high (northern) latitudes (〉35°). Annual evapotranspiration was 54% lower from the grassland (384 mm) than from the plantation (834 mm). Woody vegetation covers dominated by broadleaved-species are therefore preferred for buffering extreme high temperatures during heat waves, and recommended for rehabilitating degraded landscapes in urban areas. We also present functions for approximating α for soil-water limited conditions.
Print ISSN:
0035-9009
Electronic ISSN:
1477-870X
Topics:
Geography
,
Physics
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