Arctic rivers are controlled by a number of processes that are specific to high-latitude and cold-climate regions. Important assumed river characteristics in these areas include 1) strong seasonality of river discharge due to a short melting season, 2) high sediment supply if basins are extensively glaciated, 3) lake outbursts and ice jams favoring extreme events and river flooding and 4) pulses of water flooding the still frozen river mouth from a melting hinterland.

We defined high-latitude rivers as having their river mouth >55° North and restricted analysis to basins over 10,000 km2. 178 rivers basins were delineated from GTOPO30 DEM and total drainage area as well as relief have been mapped. Climate data and time series of monthly discharge at the lowermost gauging stations have been collected by combining ArcticRIMS, HYDAT, USGS and GRDC databases. 85% of the analyzed discharge records span over 10 years of observation, with the longest record ranging 111 years. The World Glacier Inventory data (NSIDC) and circum-Arctic map of permafrost (NSIDC) were analyzed to quantify glacier extents and relative permafrost areas for each basin. MODIS Aqua/Terra satellite imagery of 15 fluvio-deltaic systems illustrated high- and low river flow properties. The World Inventory of Dams was analyzed for presence and age of reservoirs in the selected basins.

Subsequently, we model monthly river sediment flux for all 178 systems based on specific basin characteristics (i.e. drainage area, relief and presence of lakes or reservoirs) and climate characteristics (basin-wide temperature and precipitation and snow fall statistics) as well as glacier dynamics. The model predictions are validated to observed total loads for a subset of 38 rivers, which have been monitored for sediment loads close to the river mouth. The Arctic rivers are put into perspective against a similar dataset of both observed discharge and modeled sediment load for 622 rivers worldwide.

Our data shows that Arctic rivers are indeed unique in their seasonality. We quantified seasonality as the percentage of the total water that drains over just the summer months, June-July-August (Figure 1). Seasonality strongly scales with latitude and basin temperature. High-latitude basins on average drain 53% of their total water in just three months, as compared to 26% for all basins between 55 – 0°N. We found that discharge variability, as quantified by calculating the ratio between the maximum discharge month over the mean annual discharge, has no significant trend with either latitude or basin temperature. However, the high-latitude basins as a group do stand out as rivers having a higher variability, 3,94, than all basins in the rest of the Northern Hemisphere, 3,06.

Figure 2 shows no significant relation between the ratio of glaciated area over total basin area of high latitude basins and their mean annual load. This is explained partly by the fact that the importance of glaciers, which theoretically would supply high sediment loads, scales with river drainage basin area. Relatively small basins have larger glaciated areas proportionally. These small basins are also most impacted by extreme discharge events, e.g. frequent lake outbursts due to rapid glacier melt, whereas the effects of these local events are dampened in the largest Arctic basins. On the other hand, early melting in the hinterland and river discharge draining into a still frozen deltaic region is unique to the much larger basins that stretch into lower latitudes (Figure 3). This effect is evident in most of the 10 largest Arctic river basins.

Our data corroborates that climatic warming over the last century coincides with an Arctic-wide increase in total annual river discharge. Remarkably though, seasonality of the discharge and similarly of modeled sediment loads, generally decreased over the last decade, partly due to construction of dams, but likely due to changing seasonal precipitation. We aim to better understand these complexities and the scaling relations to reliably assess circum-arctic river sediment loads to the coast.