https://doi.org/10.1016/j.jhydrol.2025.134036

Snowmelt runoff is well-recognized as important for sustaining shallow waterbodies across semi-arid and sub-humid cold regions where water loss via evaporation is relatively high, but is often overlooked in cold-region floodplains where river floodwaters are considered to drive freshwater availability. At the Peace-Athabasca Delta (northwestern Canada), drawdown of ecologically and culturally important shallow lakes is a long-standing concern. The drawdown is widely attributed to alteration of the ice-jam flood regime, but the direct influence of snowmelt runoff remains largely unknown. Here, measurements of water depth and isotope composition are used to evaluate contributions from snowmelt versus river floodwaters to lake-level rise after widespread ice-jam flooding in spring 2020. Results reveal lake-level rise from snowmelt input at non-flooded lakes (median = 0.32 m; n = 27) is comparable to that from river floodwaters at flooded lakes (median = 0.26 m; n = 25). Snowmelt accounted for more than one-third of the rise at flooded lakes. Lake-level rise by snowmelt was greatest in areas where greater topographic relief and forest/shrub vegetation entrap wind-distributed snow from adjacent flat unforested terrain. In contrast, lake-level rise by floodwater was greatest in lower elevation flood-prone areas. Meteorological records of peak snow water equivalent and melt rate reveal that comparable contributions of snowmelt runoff to lake-level rise likely occurred regularly during 1963–1987 but values in 2020 (80 mm and 10.1 mm/day, respectively) have been exceeded just once since 1987 (in 2018), suggesting drawdown of lakes during recent decades may also be associated with reduced input of snowmelt.

https://doi.org/10.1016/j.jhydrol.2025.134036