Estimation of Flood Frequencies under Changing Climate Conditions During 21st Century by means of a Numerical Coupled Atmospheric-Hydrologic Modeling Approach

Abstract:

Effect of climate change on hydrologic flow regimes, particularly extreme events, necessitates modeling of future flows in order to best inform water resources management. The presented modeling approach simulated future flows in the Cache Creek watershed in California, over the 21^st century using a hydro-climate model (WEHY-HCM) forced by future climate projections. The future climate projections, based on four emission scenarios, simulated by two GCMs (ECHAM5 and CCSM3) under several initial conditions, were dynamically downscaled using MM5, a regional climate model. The downscaled future precipitation data were bias-corrected before being input into the fully physically-based WEHY watershed hydrology model to simulate the flows at hourly intervals along the main Cache Creek branch and its tributaries during 2010-2099. The results suggest an increasing trend in flood peak discharge magnitudes at the outlet of the studied watershed throughout the 21st century. Similarly, estimates of the 100 and 200-year flood discharge magnitudes increase throughout the study period toward future in the 21st century. The differences among the historical flood frequency, and the flood frequencies during the first half and second half of the 21st century are indicative of the ongoing non-stationarity in the 21st century hydro-climate regime of the study region.