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

Abstract

Abstract. Our understanding is limited to how transient changes in glacier response to climate warming will influence the catchment hydrology in the Arctic and Sub-Arctic. This understanding is particularly incomplete for flooding extremes because understanding the frequency of such unusual events requires long records of observation not often available for the Arctic and Sub-Arctic. This study presents a statistical analysis of trends in the magnitude and timing of flood extremes and the mean summer discharge in two sub-arctic catchments, Tarfala and Abisko, in northern Sweden. The catchments have different glacier covers (30 % and 1 %, respectively). Statistically significant trends (at the 5 % level) were identified for both catchments on an annual and on a seasonal scale (3-months averages) using the MannKendall trend test. Stationarity of flood records was tested by analyzing trends in the flood quantiles, using generalized least squares regression. Hydrologic trends were related to observed changes in the precipitation and air temperature, and were correlated with 3-months averaged climate pattern indices (e.g. North Atlantic oscillation). Both catchments showed a statistically significant increase in the annual mean air temperature over the comparison time period of 1985-2009 (Tarfala and Abisko p<0.01), but did not show significant trends in the total precipitation (Tarfala p = 0.91, Abisko p = 0.44). Despite the similar climate evolution over the studied period in the two catchments, data showed contrasting trends in the magnitude and timing of flood peaks and the mean summer discharge. Hydrologic trends indicated an amplification of the streamflow and flood response in the highly glacierized catchment and a dampening of the response in the non-glacierized catchment. The glacierized mountain catchment showed a statistically significant increasing trend in the flood magnitudes (p = 0.04) that is clearly correlated to the occurrence of extreme precipitation events. It also showed a significant increase in mean summer discharge (p = 0.0002), which is significantly correlated to the decrease in glacier mass balance and the increase in air temperature (p = 0.08). Conversely, the non-glacierized catchment showed a significant decrease in the mean summer discharge (p = 0.01), the flood magnitudes (p = 0.07) and an insignificant trend towards earlier flood occurrences (p = 0.53). These trends are explained by a reduction of the winter snow pack due to higher temperatures in the winter and spring and an increasing soil water storage capacity or catchment storage due to progressively thawing permafrost.

On the variability of cold region flooding

“…Consistent with this, increasing trends in minimum flows have been observed across much of northern Sweden emphasizing the importance of the cryosphere on hydrological system's response (e.g. Dahlke et al, 2012;Sjöberg et al, 2013).…”

“…With regards to the magnitude and the occurrence of floods, variable spatial and temporal patterns have been http://dx.doi.org/10.1016/j.jhydrol.2016.01.055 0022-1694/Ó 2016 Elsevier B.V. All rights reserved. detected for northern Europe (Wilson et al, 2010;Dahlke et al, 2012;Hall et al, 2014). Wilson et al (2010) and Fleming and Dahlke (2014) showed that trends in annual and seasonal streamflow as well as changes in extreme events can be linked to precipitation and temperature trends, whereas the signal induced by temperature seems to be more clearly reflected in streamflow series.…”

“…Birsan et al, 2005;Carey et al, 2010;Lyon et al, 2010;Walvoord et al, 2012;Tetzlaff et al, 2015). The cryosphere in general and permafrost in particular have significant impact on streamflow in cold environments by buffering the hydrograph through enhanced subsurface flow causing an increase in winter base flow and a decrease in spring flood magnitude (Dahlke et al, 2012;Walvoord et al, 2012;Sjöberg et al, 2013). The discontinuous permafrost zone is particularly important for a catchment's streamflow response due to the significant ice content in the ground, which influences infiltration and transit times (Lyon et al, 2010;Tetzlaff et al, 2015).…”

Seasonal flows of international British Columbia-Alaska rivers: The nonlinear influence of ocean-atmosphere circulation patterns

“…On the one hand, the results show little systematic difference between hydrometric stations. Several studies have revealed the watershed regimedependence of streamflow teleconnections, such as profound differences in the hydroclimatology of glacierized and non-glacierized basins (e.g., [12,22,61]). However, our present outcome is not surprising, as all three rivers have broadly similar flow regimes, dominated by spring-summer snow and ice melt.…”

A DEM of the 2010 surface topography of Storglaciären, Sweden

“…Glaciohydrological studies rely on accurate topography-and surface-type distribution (i.e. the presence and extent of surface snow, firn and ice) (Dahlke, Lyon, Stedinger, Rosqvist, & Jansson, 2012;Fountain, Jacobel, Schlichting, & Jansson, 2005;Jansson, 1996;Jansson, Hock, & Schneider, 2003). Features such as glacier moulins and crevasses are also of interest for hydrological studies as well as for safety assessments but these features are transient, opening, moving and closing continuously and expressly mapping such features introduces the distinct risk of dangerously misinforming both scientists and the general public and are therefore not shown in this map.…”