Regional flood frequency analysis using GIS, L-moment and geostatistical methods

Advances in space-time tools and techniques offer new possibilities to impr ove methods for exploratory data analysis and parameter estimation in regio nal flood frequency analysis (FFA). A general framework and methodological approach are proposed which integrate concepts and techniques of regional F FA, geostatistical theory and analytical geographical information systems ( GIS) using data on climate, vegetation, geography and flood timing acid mag nitude statistics. Non-parametric methods are used to act een data and to delineate homogeneou s regions. Simulations are used to identify discordant sites, diagnose each region using the signal-to-noise ratio and lest regions for homogeneity ba sed on L-moment ratios. Geostatistical measures of spatial autocorrelation are used to diagnose hierarchical spatial models for each L-moment ratio an d to obtain map estimates of parameters using spatially explicit kriging te chniques (analogous to regression). In addition to storing and displaying t he spatio-temporal information accurately, the CIS is used to quantify spat ial associations between dependent and independent variables and to diagnos e homogeneous regions for further refinement using a simple spatial contras t measure. Analysis of data from central and eastern Canada (except the eastern parts of Newfoundland), encompassing a large area with significant random and sys tematic variability, demonstrates that: (i) map sets of L-mean and L-CV (co efficient of variation) for flood timing and magnitude can serve as indicat ors of climatic influences on the flood-generating mechanisms; (ii) models of spatial autocorrelation call be used to map point variables and their ge ostatistical spatial variance, which indicates whether maps are significant ; and (iii) associations between L-CV and snow or vegetation could support improved mapping using co-kriging or geostatistical simulations. The map-ba sed method provides parameter values at ungauged sites and maps of spatial variance that could support decisions to add or remove gauges from a hydrom etric network. Copyright (C) 2000 John Wiley & Sons, Ltd.