Estimation of near-surface air temperature lapse rates over continental Spain and its mountain areas

Although the mean environmental lapse rate (MELR) value (a linear decrease of -6.5 degrees C/km) is the most widely used, near-surface (i.e., non-free atmosphere) air temperature lapse rates (NSLRs; measured at 1.5 m height) are variable in space and time because of their dependence on topography and meteorological conditions. In this study we conducted the first analysis of the spatial and temporal variability of NSLRs for continental Spain and their relationship to synoptic atmospheric circulation (circulation weather types [CWTs]), focusing on major mountain areas including the Pyrenees, Cantabrian, Central, Baetic, and Iberian ranges. The results showed that the NSLR varied markedly at spatial and seasonal scales and depended on the dominant atmospheric conditions. The median NSLR values were weaker (less negative) than the MELR for the mountain areas (Pyrenees -5.17 degrees C/km; Cantabrian range -5.22 degrees C/km; Central range -5.78 degrees C/km; Baetic range -4.83 degrees C/km; Iberian range -5.79 degrees C/km) and for the entire continental Spain (-5.28 degrees C/km). For the entire continental Spain the steepest NSLR values were found in April (-5.80 degrees C/km), May (-5.58 degrees C/km), and October (-5.54 degrees C/km) because of the dominance of northerly and westerly advections of cold air. The weakest NSLR values were found in July (-4.67 degrees C/km) and August (-4.78 degrees C/km) because of the inland heating, and in winter because of the occurrence of thermal inversions. As the use of the MELR involves the assumption of large errors, we propose 1 zonal, 12 monthly, 11 CWTs, and 132 hybrid monthly-CWTs NSLRs for each of the mountain ranges and for the entire continental Spain. More regional studies are urgently needed to accurately assess the NSLR as a function of atmospheric circulation conditions.