Climate change is expected to modify the hydrological and
geomorphological dynamics of mountain watersheds significantly, so
impacting on downstream water yield and sediment supply. However, such
watersheds are often poorly instrumented, making it difficult to link
recent and rapid climate change to landscape response. Here we combine
unique records of river flow and sediment export, with historical
archival imagery to test the hypothesis that climate warming has
substantially increased both water yield and sediment export from small
Alpine watersheds (<3 km(2)) characterized by small (<0.5 km(2) surface)
glaciers. To examine ice and landform response to climate change, we
apply archival digital photogrammetry to historical aerial imagery
available from 1967 to present. We use the resulting data on ice loss,
in combination with reliable records of stream flow from hydroelectric
power intakes and climate data to approximate a water budget and to
determine the evolution of different contributions to river flow. We use
the stream flow records to estimate volumetric sediment transport
capacity and compare this with the volumes of sand and gravel exported
from the watersheds, quantified from records of intake flushing. The
data show clearly that climate forcing since the early 1980s has been
accompanied by a net increase in both water yield and sediment transport
capacity, and we attribute these as signals of reduced snow accumulation
and glacier recession. However, sediment export has not responded in the
same way and we attribute this to limits on sediment delivery to streams
because of poor rockwall-hillslope-channel connectivity. However, we do
find that extreme climate conditions can be seen in sediment export data
suggesting that these, rather than mean climate warming, may dominate
watershed response.