Distribuzione dell'Irradiazione Solare nel Bacino Idrografico del Torrente Roglio in Val d'Era (Toscana) [Solar Irradiation Supply on Roglio Hydrographical Basin (Val d'Era - Toscana)]

In the past decades, the Roglio hydrographical basin (160.1 km2) has been the object of a certain amount of analysis concerning its geomorphology, erosion processes related to Pliocene’s clays, hydrology and ground variations: at present a solar irradiation analysis (J/m2) is carried on in this basin. Such analysis takes into account slope grading distribution related to main cardinal directions. Irradiation supply (W/m2) has been recorded at Legoli meteorological Station in 2009. The station is situated in the heart of the hydrographical basin and has been built as a part of the big municipal controlled solid urban waste landfill plant in Peccioli. Roglio basin slope grading shows very low average values, as 82% of the physiographic units shows grades lower than 20 degrees and only 3% are higher than 30 degrees,due to the low energy of the relief and to the tendency of clay and sandy-clay formations to assume round shapes. Solar irradiation on all surfaces of the physiographic unit has been analyzed, both flat and sloping. Daily values related to global solar irradiation on flat countries (Ito > 30 MJ/m2/days) reached high values only during a short period between May and June; days with Ito > 25 MJ/m2/days occur more frequently and are recorded between April and September; the lowest values (Ito < 25 MJ/m2/days) have been reached in January, November and December. The highest yearly solar irradiation values on sloping surfaces have been reached on south exposures, with a maximum value for a sloping of 35 degrees (6.4 GJ/m2/year). In the whole, the 2009 Roglio basin incident solar irradiation has been estimated in 862.0 PJ. Uneven irradiation supply on the slopes influences temperature, ground evaporation and the speed of all processes of clay cover degradation.