Seasonal behaviour and influence of altitude on fog-water collection in the Eastern Iberian Peninsula (2003-2012)

A study on fog-water collection potential at the Mediterranean Iberian Peninsula was carried out for the period 2003-2012. The area is denoted by a high population density, with fairly common water restrictions in certain periods during the year. Moreover, climate change projections point out a sharp drop in precipitation for this sector of the western Mediterranean Basin that would aggravate water problems. This work aims to look closely at knowledge of fog-water collection and it presents results about: its behaviour during different seasons of the year; the fog-water collection potential on dry days (precipitation < 1 mm); the influence of site elevation on both collected volumes and the number of days with fog-water collection. To do so, daily fog-water collection data were analysed from 2003 to 2012 with a dense network of 23 fog-water collectors, which run along the Mediterranean coast of the Iberian Peninsula. The most relevant results were: (a) the seasonal periods with the largest recorded fog-water volumes were autumn and spring; the highest percentages of days with fog-water collection were obtained in summer and autumn; (b) on days when precipitation was null or negligible (< 1 mm), maximum daily fog-water captures were considerable and exceeded 25 L m(-2) at more than half the studied sites; (c) the greater the positive difference in elevation between nearby stations, the larger the positive difference in both fog collected volumes and fog days at equal exposition to prevailing winds, differences that increase in the summer period. Mount Muela (Murcia Region), combining a pair of stations only distanced by 600 m but at a 92-m elevation difference, reported a contrast of two times the collected volume at the upper station compared to the lower and an increment of 61% more days with fog occurrence. Mount Montseny (Catalonia), with a pair of stations distanced by 1,600 m horizontally and 398 m in elevation difference, obtained a sixfold variation between stations for fog-water collection and a 73% increment in foggy days.