Regional Flood Frequency Analysis (RFA) is widely used for reliable estimation of extreme hydrological quantiles and for flood prediction at ungauged locations. The index flood method, one of the most popular approaches for RFA, is based on the assumption that flood records are identically distributed in a homogeneous region. However, climate and land-use changes can alter flood characteristics, thereby bringing into question the assumption of stationarity in RFA. In this study, we apply a non-stationary index flood-based RFA technique for flood estimation in the state of Maharashtra in India.

Here, we first choose sites with sufficient percentage of non-missing daily flow data thereafter, catchment characteristics are obtained from digital elevation model. Mann-Kendall test is then used to identify the sites which are marked with trends in annual maximum flows. Further, we use the Region of Influence (ROI) approach to identify homogeneous regions that are similar in terms of catchment attributes that influence flood-generating mechanisms (e.g. area, mean precipitation, slope, base flow index and magnitude of trend). A non-stationary index flood-based RFA method involving transformation of records based on mathematical formulations, estimating the regional quantile and growth curve, and thereafter, obtaining the quantiles in the original space, is employed on the homogeneous regions formed. Time varying quantiles obtained are compared with that of the stationary estimates for all sites. The results reveal that, considering a stationary RFA over non-stationary analysis can lead to over(under) estimation of the design flood quantile for sites marked with decreasing(increasing) trends in the magnitude of floods.

DOI: https://doi.org/10.1061/9780784483466.021

Non-stationary Regional Frequency Analysis for Sites With Trends in Maharashtra, India

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