Turning lemons into lemonade, Sabajo et al. have used the great expansion of oil palm plantations and other crops in Indonesia to examine how such land-use change affects land surface temperature (LST). The authors observed a warming trend in the Jambi province of Sumatra of 1.05℃ and 1.56℃ in the morning and afternoon, respectively, between 2000 and 2015. The average morning (10:30 am) temperature increased by 0.07℃ per year; the midday afternoon (1:30 pm) temperature increased by 0.13℃ per year.
During roughly the same period (2000-2010), forest area decreased in Jambi by 17%, while oil palm and rubber plantations greatly expanded. Given that LST within the province’s remaining forests increased only .04C per year at 10:30 am, which the authors attribute mainly to global warming, they concluded that the overall higher province-wide daytime temperature increase was caused by the observed land cover change.
The team also compared temperatures between different land uses: forest, oil palm and rubber plantations, urban areas, and bare land. Despite having a higher albedo (reflectivity) than the forest areas, all converted (non-forest) lands were nonetheless warmer than forests, “suggesting that the albedo was not the dominant variable explaining the LST” [Sabajo 2017: 4629]. Evapotranspiration (ET) played a greater role. Non-vegetated surfaces (urban and bare) were the warmest.
The authors conclude: “The warming effect after forest conversion results from the reduced evaporative cooling, which was identified as the main determinant of regulating the surface temperature” [Sabajo 2017: 4631].
Sabajo, Clifton R., et al., 2017, Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia, Biogeosciences 14, https://doi.org/10.5194/bg-14-4619-2017