Assessment of fog gauges and their effectiveness in quantifying fog in the Andean páramo

Abstract

In tropical highlands of the northern Andes, known as páramos, fog incidence is very frequent. Its quantification is not yet clear, mostly because of the complexity of distinguishing between fog and low‐intensity rainfall. Moreover, there is uncertainty about the performance of the various types of gauges used to capture fog in this ecosystem. This study was carried out at the Zhurucay Ecohydrological Observatory (3,800 m a.s.l.), in southern Ecuador, assessing two cylindrical (Juvik and Wire Harp types) and two flat‐screen fog collection gauges. A high‐resolution laser disdrometer was installed next to the fog gauges, to measure precipitation of very low intensities and isolate fog from rainfall. We collected data over a 12‐month period for four types of events—fog only, fog dominant, fog non‐dominant and fog negligible. We evaluated the performance of the gauges during each type of event as well as to estimate the amount, rate and duration of fog. Fog was present during 68% of the days of the study, predominantly in the early morning and at night, and the average daily contribution was 1.37 mm. Most of the events occurred at rates below 0.3 mm h−1. Measured rainfall was 1,200.1 mm, and fog estimations amounted to 340.1 mm. This fog contribution could bring total annual precipitation to about 1,540.2 mm, suggesting an extra 22% of water potentially available to the ecosystem—a very important asset for hydrological and ecological processes. This is the first study that has compared different types of fog gauges in the Andean páramo.

Variability in evapotranspiration in the Andean páramo as influenced by fog and rainfall

“…This quite small decrease may be explained by the fact that fog is more prevalent in the early morning hours and dissipates when solar radiation peaks. Similar small decreases in solar radiation were found by Bittencourt et al (2019) According to Brauman et al (2010), solar radiation is more efficiently blocked by rain-bearing clouds than by foggy conditions; in other words, rainfall hinders evaporation better than does fog (Berrones et al, 2021).…”

“…Moreover, only 3% of the days were reported as foggy (fog without any other type of precipitation). In the páramo, fog‐only days are scarce; typically, fog is accompanied by other types of precipitation, mainly drizzle and light rain (Berrones et al, 2021). Only 13% of days are rainy without fog, whereas over 74% of days are characterized by fog together with light precipitation.…”

“…At our study site, reductions in radiation of this magnitude were observed during fog‐dominant days and rain‐dominant days (~35%) but not during fog‐only days. According to Brauman et al (2010), solar radiation is more efficiently blocked by rain‐bearing clouds than by foggy conditions; in other words, rainfall hinders evaporation better than does fog (Berrones et al, 2021).…”

“…Mean annual precipitation is 1210 ± 100 mm, half of which occurs at intensities of 2 mm h À1 or less (Padr on et al, 2015). Fog is very frequent in the Andean páramo-occurring 68% of the time and averaging 1.37 mm day À1 -and typically is combined with drizzle and light rain (Berrones et al, 2021). Fog can be present at any time of the day but is most common in the early morning and at night (Berrones et al, 2021).…”

“…Our study collected data from September 2017 to February 2019. Because a prior study (Berrones et al, 2021) had found that the cylindrical Juvik FG outperformed the other FGs tested (cylindrical wire harp and flat screen), we used the Juvik FG for the current study. Data from the EC tower were obtained at 30-min intervals, and fog, rainfall and meteorological data were continuously recorded at 5-min intervals.…”