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

Clouds play a major role in modulating the biometeorological processes. We studied the influence of cloudiness on four biometeorological variables: daily air temperature (T_air), relative humidity (RH), reference evapotranspiration (ET_r), 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 (K_T) using the records of solar and extraterrestrial radiation. Second, we estimated K_T from Cloud%. Finally, we quantified T_air, RH, ET_r, and PAR under clear, cloudy, and overcast K_T and their dependence on K_T. The average Cloud% ranged between 6596–76%, and K_T 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 T_air (≤ 10°C), ET_r (≤ 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 (R² ≥ 0.85), and PAR (R² ≥ 0.77) depended on K_T. Hence, the prevailing overcast sky influenced the biometeorology of the páramos.