Variable effects of forest canopies on snow processes in a valley of the central Spanish Pyrenees

Abstract

Snowpacks and forests have complex interactions throughout the large range of altitudes where they co-occur. However, there are no reliable data on the spatial and temporal interactions of forests with snowpacks, such as those that occur in nearby areas that have different environmental conditions and those that occur during different snow seasons. This study monitored the interactions of forests with snowpacks in four forest stands in a single valley of the central Spanish Pyrenees during three consecutive snow seasons (2015/2016, 2016/2017 and 2017/2018). Daily snow depth data from time-lapse cameras were compared with snow data from field surveys that were performed every 10-15 days. These data thus provided information on the spatial and temporal changes of snow-water equivalent (SWE). The results indicated that forest had the same general effects on snowpack in each forest stand and during each snow season. On average, forest cover reduced the duration of snowpack by 17 days, reduced the cumulative SWE of the snowpack by about 60% and increased the spatial heterogeneity of snowpack by 190%. Overall, forest cover reduced SWE total accumulation by 40% and the rate of SWE accumulation by 25%. The forest-mediated reduction of the accumulation rate, in combination with the occasional forest-mediated enhancement of melting rate, explained the reduced duration of snowpacks beneath forest canopies. However, the magnitude and timing of certain forest effects on snowpack had significant spatial and temporal variations. This variability must be considered when selecting the location of an experimental site in a mountainous area, because the study site should be representative of surrounding areas. The same considerations apply when selecting a time period for study. K E Y W O R D Smountain forest, snowpack, spatial and temporal variability, SWE

Elevation Effects on Air Temperature in a Topographically Complex Mountain Valley in the Spanish Pyrenees

“…The existence of snow cover in higher locations has also been mentioned as a reason for the steepening of LRmax [31], due to the albedo effect in elevated areas, in which snow cover persists during the spring months. This could explain the peak delay between the LRmax in Estiviellas (June) and Moleta (July), due to the longer snow season on the northern Moleta slope [97]. It would be very useful to advance the study of this issue in the future, and analyze the importance of this factor.…”

Performance Assessment of Optical Satellite-Based Operational Snow Cover Monitoring Algorithms in Forested Landscapes

“…1. For a recent investigation, the site offered the opportunity to look into the spatial and temporal interactions of forests with snowpack accumulated over a range of site conditions [37].…”

“…1, and are further classified by their unique site characteristics like aspect, percentage canopy cover, solar irradiance, and several other factors (Table I). [37]. one parallel to the terrain slope line) were measured for each individual pine.…”

“…However, due to the sheltering effect of the high percentage canopy cover over P1 (the highest among all the plots) the "Observed Solar Irradiance" is the lowest. The observed irradiance is logged by an automatic weather station installed at the forest opening of each plot whereas the potential irradiance is the calculated amount of radiant energy for a specific location and time period [37]. The values presented in Table I for both these irradiance measurements are averaged from March to May.…”

“…We exploited datasets from two recent investigations. One is a time-series of snow depth measurements logged during three consecutive winters in a forested valley located in the central Spanish Pyrenees mountain range [37]. This dataset enabled determination of the presence/absence of snow cover and hence was employed to evaluate the SCA algorithm.…”