Abstract
Wildfires and heatwaves have recently affected the hydrological system
in unprecedented ways due to climate change. In cold regions, these
extremes cause rapid reductions in snow and ice albedo due to soot
deposition and unseasonal melt. Snow and ice albedo dynamics control net
shortwave radiation and the available energy for melt and runoff
generation. Many albedo algorithms in hydrological models cannot
accurately simulate albedo dynamics because they were developed or
parameterised based on historical observations. Remotely sensed albedo
data assimilation (DA) can potentially improve model performance by
updating modelled albedo with observations. This study seeks to diagnose
the effects of remotely sensed snow and ice albedo DA on the prediction
of streamflow from glacierized basins during wildfires and heatwaves.
Sentinel-2 20-m albedo estimates were assimilated into a
glacio-hydrological model created using the Cold Regions Hydrological
Modelling Platform (CRHM) in two Canadian Rockies glacierized basins,
Athabasca Glacier Research Basin (AGRB) and Peyto Glacier Research Basin
(PGRB). The study was conducted in 2018 (wildfires), 2019 (soot/algae),
2020 (normal), and 2021 (heatwaves). DA was employed to assimilate
albedo into CRHM to simulate streamflow and was compared to a control
run (CTRL) using off-the-shelf albedo parameters. Albedo DA benefited
streamflow predictions during wildfires for both basins, with a KGE
coefficient improvement of 0.18 and 0.20 in AGRB and PGRB, respectively.
Four-year DA streamflow predictions were superior to CTRL in PGRB, but
DA was slightly better in AGRB. DA was not beneficial to streamflow
predictions during heatwaves. These results show that albedo DA can
reveal otherwise unknown albedo and snowpack dynamics occurring in
remote glacier accumulation zones that are not well simulated by model
predictions alone. These findings corroborate the power of observational
tools to incorporate near real-time information into hydrological models
to better inform water managers of the streamflow response to wildfires
and heatwaves.