Spatio‐temporal variability of Great Lakes basin snow cover ablation events

Abstract

In the Great Lakes basin of North America, annual run‐off is dominated by snowmelt. This snowmelt‐induced run‐off plays an important role within the hydrologic cycle of the basin, influencing soil moisture availability and driving the seasonal cycle of spring and summer lake levels. Despite this, relatively little is understood about the patterns and trends of snow ablation event frequency and magnitude within the Great Lakes basin. This study uses a gridded dataset of Canadian and United States surface snow depth observations to develop a regional climatology of snow ablation events from 1960 to 2009. An ablation event is defined as an interdiurnal snow depth decrease within an individual grid cell. A clear seasonal cycle in ablation event frequency exists within the basin and peak ablation event probability is latitudinally dependent. Most of the basin experiences peak ablation frequency in March, while the northern and southern regions of the basin experience respective peaks in April and February. An investigation into the interannual frequency of ablation events reveals ablation events significantly decrease within the northeastern and northwestern Lake Superior drainage basins and significantly increase within the eastern Lake Huron and Georgian Bay drainage basins. In the eastern Lake Huron and Georgian Bay drainage basins, larger ablation events are occurring more frequently, and a larger impact to the hydrology can be expected. Trends in ablation events are attributed primarily to changes in snowfall and snow depth across the region.

Synoptic and meteorological conditions during extreme snow cover ablation events in the Great Lakes Basin

“…As evident in Section 3.1, extreme events were only observed in December, February, and March, respectively representing 27%, 36%, and 36% of the total events. Relatively higher frequencies could be expected during these months based on the occurrence of ablation within the region (Suriano & Leathers, 2018; Suriano & Leathers, ). Peak ablation occurs in March for the GLB due to the combination of sufficient snow cover accumulated over the course of the winter season and sufficiently frequent meteorological conditions capable of ablation (Suriano & Leathers, ).…”

“…Dyer and Mote () examined ablation frequency over much of North America, including the GLB, noting a general decrease in ablation events over time for the continent. A more spatially focused study into the ablation frequency in the GLB detected a similar decrease within the northern Lake Superior drainage basin, along with a region of increasing frequency to the east of Lake Huron (Suriano & Leathers, ). Other work in the GLB details the role of three general synoptic‐scale weather types that lead to the majority of ablation: rain‐on‐snow, southerly flow, and high‐pressure overhead patterns.…”

“…The dataset interpolates daily station observations from the Cooperative Observer Network in the United States (U.S. Department of Commerce, ) and the Meteorological Service of Canada (Braaten, ), onto a 1°× 1 latitude by longitude grid (Mote et al, ). The gridded dataset is restricted to the GLB by using a centroid method, where only the grid cells whose centroids fall within the geographic boundary of the basin, as determined by the “Watershed Boundary Dataset” of the United States Geological Survey and the “Drainage Areas Dataset” of Natural Resources Canada, are retained (Suriano & Leathers, ). A single grid cell (42.5°N, 77.5°W) is added to this definition in line with Suriano and Leathers (), due to the majority of the cell being contained within the GLB, with the exception of the centroid.…”

“…The gridded dataset is restricted to the GLB by using a centroid method, where only the grid cells whose centroids fall within the geographic boundary of the basin, as determined by the “Watershed Boundary Dataset” of the United States Geological Survey and the “Drainage Areas Dataset” of Natural Resources Canada, are retained (Suriano & Leathers, ). A single grid cell (42.5°N, 77.5°W) is added to this definition in line with Suriano and Leathers (), due to the majority of the cell being contained within the GLB, with the exception of the centroid. In total, 57 1° grid cells comprise the GLB in this study (Figure ).…”

“…A snow ablation event is defined in this study as an interdiurnal decrease in GLB‐wide areal‐weighted snow depth, in excess of 2.54 cm (Suriano & Leathers, ). Following similar studies, ablation events are analysed only under situations when the maximum daily surface air temperature on the second day of the interdiurnal snow depth decrease is at least 0°C and when no more than 2.54 cm of new snowfall accumulates on any of the previous 3 days before the event (Suriano & Leathers, ).…”