A Numerical Study of the June 2013 Flood-Producing Extreme Rainstorm over Southern Alberta

Abstract

A devastating, flood-producing rainstorm occurred over southern Alberta, Canada, from 19 to 22 June 2013. The long-lived, heavy rainfall event was a result of complex interplays between topographic, synoptic, and convective processes that rendered an accurate simulation of this event a challenging task. In this study, the Weather Research and Forecasting (WRF) Model was used to simulate this event and was validated against several observation datasets. Both the timing and location of the model precipitation agree closely with the observations, indicating that the WRF Model is capable of reproducing this type of severe event. Sensitivity tests with different microphysics schemes were conducted and evaluated using equitable threat and bias frequency scores. The WRF double-moment 6-class microphysics scheme (WDM6) generally performed better when compared with other schemes. The application of a conventional convective/stratiform separation algorithm shows that convective activity was dominant during the early stages, then evolved into predominantly stratiform precipitation later in the event. The HYSPLIT back-trajectory analysis and regional water budget assessments using WRF simulation output suggest that the moisture for the precipitation was mainly from recycling antecedent soil moisture through evaporation and evapotranspiration over the Canadian Prairies and the U.S. Great Plains. This analysis also shows that a small fraction of the moisture can be traced back to the northeastern Pacific, and direct uptake from the Gulf of Mexico was not a significant source in this event.

High-resolution hydrometeorological modelling of the June 2013 flood in southern Alberta, Canada

“…From June 19 to 22, 2013, heavy rainfall and snowfall (at high elevations) with local amounts exceeding 300 mm fell over a broad region of the Canadian Rocky Mountains of southeastern British Columbia and southwestern Alberta, and the foothills and adjacent plains of southern Alberta, Canada (Milrad et al, 2015;Liu et al, 2016;Kochtubajda et al, 2016;. This heavy precipitation resulted from moisture convergence from the Pacific and from the Canadian Prairies and 5 US Great Plains through evapotranspiration (Milrad et al, 2015;Li et al, 2017). At high elevations, rain and then snow fell on a deeper than normal, late-lying snowpack leading to rain-on-snowmelt which enhanced runoff generation (Fang and Pomeroy 2016;Pomeroy et al, 2016a).…”

“…This extreme weather event has been investigated in details in the last few years from the perspectives of atmospheric and climate modelling. Li et al (2017) showed that the Weather Research and Forecast (WRF) atmospheric model at convectionpermitting resolution (3-km) demonstrated reasonable skill in simulating the spatial and temporal evolution of precipitation 15 patterns before and during the flood. They investigated with the model the dynamical features that led to the generation of heavy rainfall.…”

“…They investigated with the model the dynamical features that led to the generation of heavy rainfall. Milrad et al (2017) carried out sensitivity experiments with the WRF model at the same resolution as Li et al (2017) to determine the impacts of local topography on the extreme rainfall event. Teufel et al (2017) presented complementary results using the Canadian Regional Climate Model at lower resolution (0.11 ∘ ) than WRF.…”

“…However, their study only used daily discharges from one hydrometric station located in Calgary along the Bow River for model evaluation, and this station was heavily impacted by reservoir regulation making it unsuited 25 for this purpose. Li et al (2017) and Milrad et al (2017) did not use their high-resolution WRF simulations to generate hydrological simulations of the flood. At the local scale, Fang and Pomeroy (2016) studied in detail the impact of antecedent soil moisture and snowpack conditions on runoff generation during the flood for a small (9.4 km ! )…”

The June 2013 Alberta catastrophic flooding event – part 2: fine‐scale precipitation and associated features

“…(). Simulation of this event (Li et al ., ) illustrated the evolution of precipitation during the convective phase.…”