An Extreme Rainfall/Runoff Event in Arctic Alaska

Abstract

Rainfall-generated floods in the Arctic are rare and seldom documented. The authors were fortunate in July 1999 to monitor such a flood on the Upper Kuparuk River in response to a 50-h duration rainfall event that produced a watershed average in excess of 80 mm. Atmospheric conditions prevailed that allowed moist air to move northward over areas of little or no vertical relief from the North Pacific Ocean to the Arctic Ocean. Cyclogenesis occurred along the quasi-stationary front separating maritime and continental air masses along the arctic coast. This low-pressure system propagated southward (inland) over the 142-km 2 headwater basin of the Kuparuk River in the northern foothills of the Brooks Range; a treeless area underlain by continuous permafrost. This research catchment was instrumented with a stream gauging station, two major and six minor meteorological stations, for a total of eight shielded rain gauges. The peak instantaneous flow was estimated at 100 m 3 s Ϫ1 and was about 3 times greater than any previously measured flood peak. Historically in the Arctic, annual peak floods occur following snowmelt when the snowpack that has accumulated for 8-9 months typically melts in 7-14 days. The shallow active layer, that surficial layer that freezes and thaws each year over the continuous permafrost, has limited subsurface storage when only thawed to a depth of 40 cm (at the time of the flood). Typically for this area, the ratio of runoff volume to snowmelt volume is near 0.67 or greater and the ratio for cumulative summer runoff and rainfall averages around 0.5 or greater. For the storm discussed here the runoff ratio was 0.73. These high runoff ratios are due to the role of permafrost limiting the potential subsurface storage and the steep slopes of this headwater basin.

Contrasting trends in floods for two sub-arctic catchments in northern Sweden – does glacier presence matter?

“…Together, these results indicate the increasing importance of rainfall for flood generation. These findings are consistent with studies from Kane et al (2003) and Cunderlik and Ouarda (2009). Kane et al (2003) showed in the Upper Kuparuk River, Alaska that rainfall-generated runoff events produce flood magnitudes that can exceed by a factor of three of those generated by snowmelt.…”

“…These findings are consistent with studies from Kane et al (2003) and Cunderlik and Ouarda (2009). Kane et al (2003) showed in the Upper Kuparuk River, Alaska that rainfall-generated runoff events produce flood magnitudes that can exceed by a factor of three of those generated by snowmelt. They concluded that the likelihood of major rainfall-generated floods is especially prevalent in catchments with limited soil storage and steep topography.…”

“…They concluded that the likelihood of major rainfall-generated floods is especially prevalent in catchments with limited soil storage and steep topography. However, catchment size and the orientation of the catchment to predominant weather patterns are also important factors (Kane et al, 2003). Similarly, Cunderlik and Ouarda (2009) reported that the importance of rainfall floods has been increasing across continental arctic and sub-arctic Canada during the past three decades, while magnitudes of snowmelt floods showed significant negative trends.…”

“…This may lead to a greater importance of rainfallrunoff flood events, especially if changes occur in the magnitude or intensity of severe rainfall events (Burn et al, 2010). Kane et al (2003) for example found for the Upper Kuparuk watershed in Alaska that a few high-intensity precipitation events appear to generate greater runoff volumes (three times greater) than a large number of low intensity events. They hypothesized that these minor precipitation events may be important in priming the watershed for the high magnitude events by filling water storages.…”

Seasonal and hydrologic drivers of dissolved organic matter and nutrients in the upper Kuparuk River, Alaskan Arctic

“…In contrast, peak discharge in small headwater streams, such as the upper Kuparuk, is less predictable. There is a peak in discharge during the spring thaw, but often, large storm events later in the summer produce comparable or even larger peaks in discharge (Kane et al 2003(Kane et al , 2008.…”