Snowtography quantifies effects of forest cover on net water input to soil at sites with ephemeral or stable seasonal snowpack in Arizona, USA

Abstract

Forested, snow-dominated watersheds provide a range of ecosystem services including water supply, carbon sequestration, habitat and recreation. While hydrologic partitioning has been well-studied in watersheds with stable seasonal snowpack, less is known about watersheds with ephemeral snowpack. Furthermore, drought-related disturbances and/or management practices are altering vegetation cover in many forests, with unknown and potentially different, consequences for stable seasonal versus ephemeral snowpacks. This study quantifies net water input (NWI) to soil for two sites with contrasting stable seasonal and ephemeral snowpacks, respectively, for three water years in Arizona, USA. Observations include a network of automated cameras and graduated snow stakes (snowtography) deployed across gradients of forest structure, airborne lidar maps of topography and forests and SNOTEL station records. Given the importance of mixed-phase precipitation in ephemeral snowpack watersheds, an algorithm is developed to distinguish among snowfall and rainfall that does/does not contribute to snowpack mass. Finally, existing canopy interception and snowpack models are used to estimate how NWI varies with canopy cover. At the ephemeral snowpack site, increasing canopy cover reduces NWI amount and advances its seasonal timing less strongly than at the stable seasonal snowpack site.Interestingly, canopy reduces NWI duration at the ephemeral site but prolongs it at the stable seasonal snowpack site. These effects are more important in a cool/wet and average year than a warm/dry year. Understanding differences between canopy impacts on amount, timing and duration of NWI for areas with ephemeral versus stable seasonal snowpack is increasingly important as the number of watersheds with ephemeral snowpack grows.

Modeling Forest Snow Using Relative Canopy Structure Metrics

“…Canopy affects site-specific physical processes that drive snow retention and melt in a manner hard to model at a variety of scales [29,46]. There is a growing body of work highlighting the interactions between the orientation of trees and the sub-canopy energy budget [29,35,56,[65][66][67]. As highlighted in the introduction, many of these interactions have been modeled at a fine scale [50,51,68].…”

The Influence of Winter Snowpack on the Use of Summer Rains in Montane Pine Forests Across the Southwest U.S.

“…As Dwivedi et al. (2023) illustrates, factors such as tree density and snow accumulation patterns can significantly influence root stress and the infiltration capacity of soils. It is vital to incorporate these variables in future studies to develop a comprehensive understanding of forest response to extreme and prolonged drought conditions.…”

“…In the montane forests of the western U.S., peak soil moisture closely follows the date of snow disappearance (Bales et al., 2011; Harpold et al., 2015), which has been found to be an important source of water for trees in the early spring (Nehemy et al., 2022). Thus, the magnitude and melt timing of snowpack can impact spring and summer available soil moisture (Dwivedi et al., 2023; Hamlet et al., 2007; Tang & Feng, 2001). For example, years with larger snowpack lead to a later melt‐out date, culminating in high soil moisture throughout the growing season, while years with smaller snowpack lead to an earlier melt‐out date, culminating in low soil moisture throughout the growing season (Kumar et al., 2019; Tang & Feng, 2001).…”

Virtual snow stakes: a new method for snow depth measurement at remote camera stations

“…Remote cameras are fine scale in both time and space (e.g., detections at < daily intervals in <100 m viewsheds), collect data remotely with minimal maintenance, can be deployed almost anywhere, and are relatively inexpensive to purchase and operate relative to common hydrometeorological equipment such as ultrasonic depth sensors with associated data loggers (Steenweg et al 2017). Cameras with physical snow stakes installed in the camera viewshed have been successfully used to collect snow depth data in several snow studies (Dickerson‐Lange et al 2017, Sirén et al 2018, Bongio et al 2021, Dwivedi et al 2022). Thus, cameras used for wildlife studies have the potential to simultaneously be used to derive snow data, providing valuable snow information spanning diverse and complex landscapes that provide critical wildlife habitat.…”