Drainage Basin Sensitivity to Climate Change in the Eastern Italian Alps

Abstract:

In the past decades, increases in summer air temperatures generate glacial-melt floods with higher than normal magnitudes, increase the frequency of high intensity rainfall events, and lead to permafrost degradation of steep rocky slopes prone to mass wasting. Continued climatic warming has the potential to drastically increase the sediment supply to the channel network. A US-Italy collaboration is characterizing response domains for drainage basins undergoing deglaciation in the Italian Alps to develop sensitivity indices of changes in flow and sediment dynamics. Six glaciated basins 85-160 km² in size within the upper Adige River Valley are analyzed. Three study basins have multi-year data on either the spatial distribution of mass wasting and sediment production or hydrology and sediment transport over snow and glacial melt, or both. The other three basins are tested for applicability of the sensitivity indices where field data are lacking. Preliminary results indicate basin lithology and degree of sediment connectivity are the dominant controls on drainage basin response. Four broadly applicable response domains incorporate metamorphic, sedimentary, or mixed bedrock lithology with high to low connectivity. The sensitivity indices for fluvial response are controlled by valley confinement and channel morphologic changes. A historic topographic map from 1858 provides qualitative channel geometry information at the end of the Little Ice Age and glacial extent for all basins. Aerial photographs from 1945, 1954, 1971, and lidar and imagery from 2005 or 2011, along with field verification quantify valley confinement, braiding index and sediment connectivity. Key controls on sediment delivery to channels include glacially-inherited topography and the distribution of glacigenic surficial materials. Sediment cascade modeling will identify sediment sources, pathways and sinks and provide a first order understanding of basin-scale response to climate change.