Overcast sky condition prevails on and influences the biometeorology of the tropical Andean Páramos

Abstract

Clouds play a major role in modulating the biometeorological processes. We studied the influence of cloudiness on four biometeorological variables: daily air temperature (Tair), relative humidity (RH), reference evapotranspiration (ETr), and photosynthetic active radiation (PAR), recorded at four sites of Andean Páramos in southern Ecuador during 2.5 to 5.5 years. First, we quantified both the cloud cover percentage (Cloud%) creating cloud masks over the visible bands of Landsat 7 images and the sky condition (KT) using the records of solar and extraterrestrial radiation. Second, we estimated KT from Cloud%. Finally, we quantified Tair, RH, ETr, and PAR under clear, cloudy, and overcast KT and their dependence on KT. The average Cloud% ranged between 65%–76%, and KT corroborated the prevailing overcast sky (between 55% and 72.5% of the days) over the páramos. The proposed model performed well in the sites of calibration (R2 = 0.80; MBE = 0.00; RMSE = 0.05) and validation (R2 = 0.74; MBE = -0.07; RMSE = 0.11). The overcast sky diminished Tair (≤ 10oC), ETr (≤ 1.6 mm day-1), and PAR (4 MJ m-2 day-1) and increased RH (≥ 88%), while the variables showed the opposite behavior during the uncommon clear sky (≤ 5.5% of the days). Thus, mostly the dynamic of RH (R2 ≥ 0.62), ETr (R ≥ 0.85), and PAR (R2 ≥ 0.77) depended on KT. Hence, the prevailing overcast sky influenced the biometeorology of the páramos.