Franco Miglietta

Research project

Albedo-modifying properties of olive trees in Mediterranean climate: ecological, climate change and water savings implications

Project summary

Many Mediterranean schlerophyllous species have peculiar characteristics of their foliage. For instance native as well as cultivated species belonging to the Olea and Quercus genera have leaves that differ substantially in the optical properties of the upper (adaxial) and lower (abaxial) leaf surfaces. The upper surface is normally darker than the lower surface and this is mainly due to the presence of a dense hairy structure in the abaxial surface which reflects more light in the visible region. Under calm conditions (low wind and turbulence) the upper leaf side is exposed to sun while wind gusts that modify the architecture of the tree canopy often expose the lower leaf surface to incoming direct irradiance. As a consequence, windy conditions lead to an increase in the canopy albedo. Wind-driven changes in the spatial arrangement of the leaves can be responsible for a 0.02 change in albedo. Increased reflectance and, hence, reduced radiation absorbance can cause a detectable decrease in the upward longwave emission of the foliage. The Oleα project intends to further explore wind-albedo interactions in olive trees with multiple objectives:I. Measure difference in reflectance/transmission of light of abaxial & adaxial leaf surfaces in different Olea europea cultivars and investigate how Δα varies with tree age and the aridity of the sites where olive trees are grownII. Assess how turbulence quantitatively affects instantaneous α of mature field grown olive trees through changes in leaf orientation and the relative exposure of the two leaf surfaces to direct radiationIII. Explore, by means of modeling (LPJmL model), how changes in Δα are likely reflected by changes in yield and productivity of olive orchards in the Mediterranean regionIV. Parameterize and eventually upscale wind-albedo relationship to propose specific guidelines to maximize climate mitigation potentials achievable by the reduction of the RF of olive trees plantation in the Mediterranean region.