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

Authors: Dwivedi, Ravindra; Biederman, Joel; BROXTON, P.D. - University Of Arizona; LEE, K.L. - University Of Arizona; VAN LEEUWEN, W.J. - University Of Arizona

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2022
Publication Date: 10/18/2022
Citation: Dwivedi, R., Biederman, J.A., Broxton, P., Lee, K., van Leeuwen, W. 2022. Snowtography quantifies effects of forest cover on net water input to soil at sites with ephemeral or stable seasonal snowpack in Arizona, USA. Ecohydrology. 16(2). Article e2494. https://doi.org/10.1002/eco.2494.
DOI: https://doi.org/10.1002/eco.2494

Interpretive Summary: High-elevation forested watersheds provide a wide range of ecosystem services including water supply, carbon sequestration, habitat and recreation. Forest structure exerts strong control on how precipitation is partitioned among evaporative losses, streamflow, groundwater recharge, and water for forests. While the effects of forest structure on snowpack have been well-documented, less is known about the subsequent amount and timing of snowmelt water inputs to soil. Here, we compare and quantify climate-forest-snow interactions across a range of forest disturbance and management at two sites in Arizona, USA, and quantify how forests affect the amount and timing of net water input to soil. This work showed that as canopy cover increases, there is a steeper reduction in net water input at the high- than at the lower-elevation site. In total, this study improves current understanding of forest structure impacts on hydrologic partitioning and could be used to inform forest management practices.

Technical Abstract: Forested, snow-dominated watersheds provide a range of ecosystem services including water supply, carbon sequestration, habitat and recreation. While hydrologic par- titioning 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 for- ests, with unknown and potentially different, consequences for stable seasonal ver- sus 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.