Cloud water interception in the temperate laurel forest of Madeira Island

Abstract

A cloud belt frequently forms on the windward side of Madeira Island, between 800 and 1600 m a.s.l., as a result of adiabatic cooling of the northeastern trade winds that are forced upward. Temperate laurel forest is the most common vegetation inside that cloud belt altitudinal range. Cloud water interception was estimated by comparing precipitation and throughfall during a hydrological year. It totalled 200 mm (8% of rainfall) during 65 days (3 mm d -1 ) and seems to constitute a larger fraction of water input during drier months. Multiple linear regression between gauge standard deviation and throughfall throughout rain events shows that cloud interception is common before the onset of rainfall. Its role in the ecohydrology of laurel forest and in the island's hydrology should be acknowledged. Further studies on this issue should be a priority in order to better understand these dynamics and provide tools for the correct management of this protected forest and the island's groundwater resources.

Reply to 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

“…Further references to this fact can be read throughout the paper. RR argue that, when compared with other places in the world, fog precipitation (cloud water interception) in Madeira's high‐altitude tree heath forest is abnormally high. In Table , we compare the information obtained in the different studies referred by RR (Kämmer, ; Regalado and Ritter, 2010; Ritter and Regalado, ) and P12, plus another recent one about Madeira's humid laurissilva (Figueira et al ., ). The first part of P12 was made in a windward first‐line (first row of individual plants along a windward exposed edge of a vegetation patch) old‐growth heath tree that is fully exposed to fog and wind and, obviously, does not represent the entire forest.…”

“…Usually, in the high altitudes of Madeira Island, rain (orographic or frontal) is accompanied by fog (the cloud touches the ground). Cloud water interception also occurs during rain events and is common before their onset (Figueira et al ., ). Madeira Island has higher mean rainfall values than any of the Canary Islands, and Bica da Cana , in particular, is much wetter than any other place in the Canaries.…”

“…In this way, the mean cloud water input in the whole forest is considerably lower than the one registered in the first line (Table ). For example, inside a continuous stand of Madeira's temperate laurissilva, cloud water was found to represent 9.6% of annual throughfall (Figueira et al ., ) and inside a secondary tree heath forest, 13% of annual throughfall (Prada et al ., ). These are very similar to the results (11% of throughfall) obtained in Garajonay Park (Regalado and Ritter, 2010; Ritter and Regalado, ).…”

“…The same pattern is also referred in the work of Figueira et al . (). We consider the measured cloud water values in the high‐altitude tree heath forest to be very high.…”

“…The results for temperate laurissilva in the work of Prada et al (2009) show that during winter, cloud water interception is 11% of the registered water under the vegetation, whereas in summer, it is 33%, even though it has a lower total. The same pattern is also referred in the work of Figueira et al (2012). We consider the measured cloud water values in the high-altitude tree heath forest to be very high.…”