Prospects for Season-ahead Global Flood Forecasts

Abstract:

Flood events rank as one of the most destructive natural hazards, with associated global economic losses increasing starkly over the past half century. This has drawn attention to prospects for flood forecasts to protect life and livelihoods. Typical forecasts emphasize the short-term (hours to days) scale to inform immediate response action. Longer-range forecasts, on the order of months to seasons, however, could compliment short-range forecasts by focusing on disaster preparedness. Initially, we define key flood seasons globally, at grid and basin scales, which are most likely to contain the most severe annual flood using observational (GRDC) and model (PCR-GLOBWB) streamflow data over 1958-2000. Model–defined flood seasons strongly agree (89% of time) with flood seasons defined through observations. Model–defined flood seasons were also qualitatively verified with actual flood records over 1985-2008 from the Dartmouth Flood Observatory records. Subsequently we have begun investigating the effects of inter-annual climate variability on seasonal maximum floods, particularly how ENSO and other large-scale phenomena may modulate discharge and flood severity. Skillful relationship have led to preliminary seasonal global flood forecast models, at the basin scale, providing early (season-ahead) flood probabilities, flood extent, and estimated damages.