Lessons from Urbanization in Understanding Potential Channel Response to Climate Change

The magnitude and rate to which fluvial landscapes will response to climate change could directly impact many human communities and ecosystems. Climate induced changes to natural flow, sediment, wood and riparian vegetation will lead to a range of potential channel responses. In glaciated basins where there are significant increases in sediment supply channels will aggrade and increase the frequency of flooding. In watersheds subjected to increased rainfall and minimal increases in sediment supply, channel response may mirror the impacts induced by urbanization. Agriculture, urbanization, riparian and channel clearing, and river impoundments are all examples of human alterations of flow and sediment regimes that go on to influence channel response. These actions may provide some clues on what to expect as streams and rivers respond to climate change. Evidence from rivers in the Pacific Northwest indicates that rapid glacial retreat is increasing sediment supply beyond the transport capacity of some rivers despite increases in the magnitude and frequency of peak flows. This is resulting in bed aggradation and increased flood frequency. Riverbed aggradation is altering entire valley bottoms, burying old growth riparian forests and overwhelming infrastructure constructed with assumptions about flow, sediment and wood regimes that are no longer valid. Successful river management will depend on setting realistic goals in the context of landscape response to human development and climate change. River management will increasingly need to accommodate and possibly moderate, the effects changing flow and sediment regimes. Successful design will accept and integrate change by defining fluvial disturbance corridors and evaluating how different corridors have responded to the impacts of urbanization. Recent research demonstrates that maintaining vegetated riparian areas has been an important element in mitigating the impacts of land development and likewise be critical with respect to mitigating the impacts of climate change.