Flood Quantiles and Changing Climate: Seasonal Forecasts and Reconstruction of Past Flood Records

It is widely acknowledged that both climate and land use changes modify flood frequency, thereby challenging the traditional assumption that the underlying stochastic process is stationary in time, and that the annual maximum flood corresponds to an independent identically distributed (iid) process. In this paper, we employ a semi-parametric approach to estimate flood quantiles conditional on selected "climate indices" that carry the signal of structured low frequency climate variation, and influence the atmospheric mechanisms that enhance or retard local precipitation and flood potential. The semi-parametric approach that maximizes the local likelihood of the observed annual maximum peak in the climatic predictor state space is applied to estimate conditional flood quantiles for the Blacksmith Fork River near Hyrum (BFH), Utah. The estimated conditional flood quantiles correlate well with the observed annual maximum peaks, thus offering prospects for reconstructing past flood series as well as for short term forecasting.