Temporal variation of climate in the high-elevation páramo of Antisana, Ecuador

Abstract

We monitored the climate in high-elevation páramo of Antisana (Ec- uador) to analyze its diurnal and annual variation. We established two cli- matic stations on the western (leeward) side of the mountain at 4280 m and 4600 m, and two stations on the north-eastern (windward) side at 4120 m and 4430 m. We recorded air temperature at 100 cm above ground, relative air humidity, and global solar radiation in hourly intervals from July 2007 to December 2010. Moreover, we recorded precipitation at the two lower stations. The western side received 1098 mm of rainfall per year with two maxima in April–June and October–November. In contrast, the north-eastern side received 2694 mm with a single maximum in June. The air was almost permanently saturated with moisture, both during the day and the year, on the north-eastern side with mean relative air humidity of 98%. On the western side, the air humidity showed distinct daily and sea- sonal variation; it dropped to 80% at noon and had two annual minima in January and September. The western side of Antisana received 35% more solar radiation than the north-eastern side. Furthermore, the mostly cloudy weather on the north-eastern side tended to eliminate the mid-day maxi- mum of radiation. The stations at higher elevations received 11% more solar radiation than the stations at lower elevations and experienced a more distinct seasonal variation with the maximum during August–September. Mean annual air temperature varied within 2K at all stations, which con- trasted with the mean daily oscillation of 8–10K on the western side and 5K on the north-eastern side. Night frosts were frequent on the western side whereas high humidity and cloudiness on the north-eastern side reduced the number of frost nights. Frosts were rather mild and of short duration; the minimum temperature recorded was –6.1°C and most frost periods lasted less than four hours. Freezing temperatures were most frequent dur- ing periods of reduced humidity. Temperature lapse rates calculated for the 300 m elevational gradient were 0.44 K/100 m and 0.55 K/100 m for the western and north-eastern sides, respectively. Potential evapotranspiration values suggested that water was in surplus year-round on the north-eastern side of Antisana, but its availability was limited during drier periods on the western side.