Influence of atmospheric circulation changes and regional climate variability on river flow and suspended sediment fluxes in southern Iceland
Authors: Lawler D. M. , McGregor G. R. , Phillips I. D. 
Published: November 2003

Only a few studies have attempted to link climate variability to glaciofluvial sediment transport, and none has incorporated atmospheric circulation changes quantitatively. This is the first attempt to do this. Using a statistical approach for three Icelandic basins, we establish some hypothesized interactions forming a chain of causality running from recent atmospheric circulation changes in the North Atlantic, through regional climate implications in southern Iceland, likely glaciological, nival and geomorphological impacts, hydrological responses, and finally to influences on suspended sediment fluxes. Furthermore, to provide some form of experimental control, the three glacierized basins chosen (the Jökulsá á Sólheimasandi, the Holmsá and the Skógá in southern Iceland) exhibit minimal anthropogenic disturbance and negligible land‐use change over the study period (1973–92). This helps to avoid the problem of disentangling the effects on sediment loads of concurrent land‐use change and climate change, which often affect this type of study. We develop the study beyond the annual and seasonal patterns and focus on subseasonal (monthly) and daily event time scales, for which useful instrumental records are available.

Suspended sediment loads in the Jökulsá á Sólheimasandi and Holmsá basins are high, but have declined significantly at a semi‐logarithmic rate over the 1973–92 period, typically from 14·6 to 7·6 kg s−1 and from 40 to 10 kg s−1 respectively. Decreases are most notable in spring and autumn. Declines are related to significant river flow reductions driven by significant cooling in spring and decreases in heavy daily precipitation events in autumn, which are only modestly offset by increases in flow and suspended sediment transport in summer and January. The annual melt‐season thus appears to be starting later and becoming more compressed. In particular, spring cooling through the 1973–92 period (e.g. April air temperatures decline at 0·99 °C decade−1) is linked to a switch to a positive North Atlantic oscillation (NAO) index since the early 1970s and a slight tendency for a weakening of the southwesterly circulation over Iceland. This is likely to subdue rates of ablation, glacial drainage network expansion and debris melt‐out in spring. Summer warming is significant (e.g. June air temperatures rise by 0·45 °C decade−1), as is the tendency for January to become warmer and wetter, with higher discharges. Suspended sediment loads and discharge seem to be sensitive to subtle shifts in climatic seasonality influenced by circulation changes. However, it is shown that flow and sediment transport responses to climatic variability and change are highly complex and demand at least a subseasonal analysis. The results, therefore, provide useful insights into the workings of glaciofluvial sediment transport environments in the presence of climate and circulation variability but in the absence of land‐use change. Copyright © 2003 John Wiley & Sons, Ltd.