Browsing by Author "Wilcox, Bradford P."

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Assessment of fog gauges and their effectiveness in quantifying fog in the andean páramo
(2021) Célleri Alvear, Rolando Enrique; Wilcox, Bradford P.; Berrones Guapulema, Gina Marcela; Tobon, Conrado; Crespo Sánchez, Patricio Javier
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
Effects of heavy grazing on the microclimate of a humid grassland mountain ecosystem: insights from a biomass removal experiment
(2022) Carrillo Rojas, Galo José; Wilcox, Bradford P.; Montenegro Díaz, Paola Fernanda; Célleri Alvear, Rolando Enrique
In high-altitude Andean grasslands (páramo), overgrazing leads to alterations in both vegetation and microclimate. These alterations need to be identified to devise land management strategies that will preserve and enhance ecosystem processes. To elucidate this issue, we designed an overgrazing experiment: we selected two plots covered with native grass (pajonal), in one of which we mowed to the ground surface. We left the second plot undisturbed to serve as a control. For both plots, we continuously monitored albedo and ancillary energetic components to generate quarterly and yearly comparisons for the following parameters: (a) impacts on albedo and resilience of grass; (b) radiative forcing of albedo; and (c) land surface temperature feedback during the recovery period. In the first quarter following removal, when the soil was covered with light litter, median albedo increased 38.81% (0.16 ± 0.02), then began a gradual decrease, which continued until its full recovery 1.75 years later (0.10 ± 0.01). During the first year of the experiment, a strong mean negative instantaneous radiative forcing was observed (−7.08 ± 6.03 Wm−2), signifying a reduction in net shortwave energy. This forcing returned to normal, pre-intervention conditions (−0.55 ± 0.97 Wm−2) after 1.75 years, equal to the energetic recovery period of the grass. Both the amount (from 133.0 ± 44.72 to 119.67 ± 39.30 Wm−2) and the partitioning (net shortwave decreased 5%; net longwave increased 9.7%) of net energy were altered after removal, evidence of cooling feedback during the recovery period. This feedback indicated that the decrease in albedo (1.25%) or instantaneous radiative forcing (−4.67 Wm−2) resulted in a decrease in land surface temperature of 1 °C. Thus, our overgrazing experiment without soil destruction followed by a natural recovery time has identified the energetic recovery period for grass in the páramos; suggesting the albedo as a good indicator of grass resilience.
Importance of Fog and Cloud Water Contributions to Soil Moisture in the Andean Paramo
(2022) Berrones Guapulema, Gina Marcela; Célleri Alvear, Rolando Enrique; Wilcox, Bradford P.; Ochoa Sánchez, Ana Elizabeth; Crespo Sánchez, Patricio Javier
Páramos are particular ecosystems of the Tropical Andes, where fog and low-intensity rainfall such as drizzle are commonly frequent—but the contribution of these water sources to soil water replenishment and discharge is not yet clear, mainly because the development of techniques for separating fog from drizzle and wind-driven rainfall has been challenging. Fog was measured with a cylindrical Juvik gauge and types of precipitation other than fog with a high-resolution disdrometer. Soil moisture was measured at 100 mm depth by means of Water Content Reflectometers, then Effective precipitation (EP) was calculated. We categorized events as two types: fog only (FO) and cloud water (CW). We found that in the case of FO events, only small amounts reached the soil (EP ranged between 0.1 and 0.2 mm); in contrast, greater amounts of EP originated from CW events (maximum value of 4.3 mm). Although we found that FO events are negligible for stream water contribution; they are ecologically important for maintaining high relative humidity, low net radiation, and consequently low evapotranspiration rates. Our research provides new insights into the hydrological role of fog, enabling us to better understand to what extent its input influences the water resources of the Andean páramo.