Cloud water interception in the high altitude tree heath forest (Erica arborea L.) of Paul da Serra Massif (Madeira, Portugal)

Abstract

Abstract:Cloud water interception (CWI) occurs when cloud droplets are blown against the forest canopy, where they are retained on the vegetation surface, forming larger water droplets that drip into the forest floor. CWI was measured from 1 October 1997 to 30 September 1999, on a first-line tree heath (Erica arborea), at Bica da Cana, Madeira Island. Rainfall was corrected for wind-loss effect and compared with throughfall and other climatological normals. The CWI depletion rate along a forest stand transect was also analysed during three distinct fog events in 2008. Cloud water was 28 mm day 1 , corresponding to 68% of total throughfall and 190% of the gross precipitation. Cloud water correlates directly with monthly normals of fog days and wind speed and correlates inversely with the monthly air temperature normal. CWI has an exponential correlation with monthly relative humidity normal. Cloud water capture depletion along the stand shows a logarithmic decrease. Although a forest stand does not directly relate to a first-line tree heath, this study shows that CWI is a frequent phenomenon in the Paul da Serra massif. Restoration and protection of high altitude ecosystems in Madeira should be a priority, not only for biodiversity, ecological and economical purposes but also for its role in regional water resources.

PARTITIONING OF RAINFALL IN EXPERIMENTAL PLANTATIONS OF Eucalyptus urophylla AND Pinus elliottii

“…In sites with frequent fog, such as Cunha, net precipitation can also overcome rainfall as a result of occult precipitation, i.e., capture and dripping of water from the fog through the treetops (GOMEZ-PERALTA et al, 2008;PRADA et al, 2012). An indication of the occurrence of occult precipitation in eucalyptus is the fact that of the 415 events recorded during the study, throughfall water was collected without the presence of gross precipitation on 16 occasions, totaling 3.7 mm.…”

“…Although no anemometric measurements were taken in the present study, during field observations it was observed that the crowns of eucalyptus trees were more susceptible to wind action than pine trees. The movement of the leaves and branches is essential for the dripping of intercepted fog water (PRADA et al, 2012).…”

Comment on Prada et al. 2012. ‘Cloud water interception in the high altitude tree heath forest (Erica arborea L.) of Paul da Serra Massif (Madeira, Portugal)’. Hydrological Processes 26: 202–212

“…Prada et al . () quantified cloud water interception or fog water dripping from a heath tree ( Erica arborea L.) forest in Bica da Cana (Madeira): maximum values of around 200 mm day −1 , mean daily values of 28 mm day −1 and average yearly cumulative fog values of 4169 mm year −1 during a 3‐year period (1997–1999). These data were obtained using only two gauges (0.357 m diameter; 0.10 m 2 collecting area); one placed leeward and the other windward under an individual exposed E. arborea tree.…”

“…Although Prada et al . () acknowledged the insufficiency of the number of gauges they used, they claim to have checked data ‘consistency’ by comparing their fixed arrangement with data obtained using three larger (0.28 m 2 collecting area) roving gauges. No details about the methodology (relocation frequency, number of roving positions, spatial location of repositioned gauges, etc.…”

“…), or the analyses carried out were provided in Prada et al . () with regard to their roving experiment. To describe the roving experiment, they refer to a response to a comment on another article (Prada et al ., ) that we presented earlier (Regalado and Ritter, ).…”