Estimating Change in Flooding for the 21st Century Under a Conservative RCP Forcing: A Global Hydrological Modeling Assessment

Flooding is the most common natural hazard worldwide. While some events are seasonal, large floods are episodic making flood dynamics difficult to predict. Recent modeling advances of river-floodplain interactions do provide first-order estimates of magnitude, frequency, and duration of floods. Here we develop new capability for the Water Balance Model to quantify location, frequency, and magnitude of flooding, and potential impact of future climate on these characteristics. Bankfull water discharge is determined for each river location using the 2-year flood recurrence interval driven by bias-corrected climate simulations of the Inter-Sectoral Impact Model Intercomparison Project. Similarly, discharge thresholds that occur at the 5-, 10-, 25-, 50-, 100-, and 200- year flood recurrence intervals are determined. We demonstrate that most river reaches of central North America and Europe experience fewer floods toward 2100, with recurrence intervals of 10 years, when applying a specific climate scenario (RCP4.5). In contrast, under this conservative climate forcing, river reaches in northeast India and East Asia experience flood intensification. When analyzing flood frequency per recurrence interval, we found there will be an increase for most continents for most recurrence intervals by 2100, but notably this increase is only observed for the higher recurrent intervals for Europe.