Can We Adequately Quantify the Increase/Decrease of Flooding Due to Climate Change?

Changes in global climate may have significant impacts on local and regional hydrological regimes. Consequences of these changes may in turn result into potentially significant impacts on flooding occurrence and severity, as well as more or less prolonged droughts. Adaptation strategies, including revisiting engineering design standards and practice, as well as developing innovative water management approaches, will need to be devised to cope with potentially deleterious impacts consequential to shifts in climate. It is therefore imperative to capitalize on the latest and finest tools to quantify impacts of climate change on river flows. A number of studies investigated the potential impacts of climate change on river flooding. Most are directly or indirectly based on linking General Circulation Models (GCM) outputs to hydrological models to generate current and anticipated river flows. The approach suffers from the low spatial and temporal resolution of GCMs which is not suitable for carrying hydrological studies on all but a few watersheds. The number of GCMs and climate scenarios adds to the uncertainty in quantifying watershed hydrological response to climate change. Downscaling techniques, either dynamical or statistical, offer new perspectives for conducting climate change impact studies, as they are used to bridge the spatial and temporal resolution gaps between climate models and what impact assessors need. However, most downscaling methods have problems dealing with the uncertainty linked to models and emission scenarios. This paper presents results from one possible approach and discuss the implications for flood estimation in the snowmelt period and summer/fall season.