Fog in the andean páramo: measurements, dynamics, and its influence on soil hydrology and evapotranspiration processes

Abstract

The páramo ecosystem is characterized by a very moist climate and the continuous presence of fog and low-intensity rainfall. The most important páramo feature is the high water regulation capacity which in part might be related to the high frequency of fog and low-intensity rainfall (drizzle). Therefore, it is essential to understand the hydrological processes that are linked to the ecology of the páramo. This study aimed the following three objectives: (1) to assess fog water estimates derived from three different types of fog gauges, and from them to understand its temporal dynamics and the importance of fog to annual rainfall; (2) to quantify the contribution of fog water deposition to soil moisture; and (3) to analyze the impact of fog on evapotranspiration rates, under different weather conditions (clear, foggy and rainy). Findings of this study show that fog occurs at very low intensities (0.2 mm h-1) reporting events of short term (<3 hours) at wind velocities below 4 m s-1. Most of the time fog appears combined with other type of precipitation (i.e. drizzle, light rain or rain) with fog tending to be more intense in the early morning, and at night. On average, daily fog amounts 1.37 mm. Overall, fog and drizzle are the major water sources to páramo vegetation, especially during late night-time and early mornings, when evaporation is low. The fog water deposition shows that only 4.5% of fog reaches the soil, contributing to soil moisture changes rather low (0.1-0.2 mm), whilst the combination of fog with low-intensity rainfall generate a higher contribution on soil moisture (as high as 4.3 mm). These events are potentially important for both soil moisture and stream flow, because of their long duration and high total amount per-event. Daily evapotranspiration rates are reduced by 43% due to the presence of mixed conditions (fog + lowintensity rainfall) compared with clear conditions (no fog and no rainfall). The net radiation is reduced by 9.2% during foggy conditions (only fog) mainly because its early morning hours occurrence is higher, and when solar radiation peaks fog occurrence is lower. While, during mixed conditions the net radiation is reduced by 33%. At the same time as less humid periods were reported, evapotranspiration was also low; suggesting that fog and drizzle presence can inhibit transpiration, limit water loss by evaporation and also could alleviate water stress.