01 July 2019

Coupled Flow Accumulation and Atmospheric Blocking Govern Flood Duration

The synergy between a large persistent low-pressure blocking system in the atmosphere and a higher rate of divergent wind often triggers a long-duration flood.

Science

Our preliminary survey showed that most of the recent flood-related studies did not formally explain the physical mechanisms of long-duration flood events that can evoke substantial damages to properties and infrastructure systems. We have shown in this investigation that long-duration floods can be related to persistent variables in the hierarchy of the climate and atmospheric system. Long-duration floods are triggered by high antecedent flow conditions, which are in turn caused by high moisture release from the recurrent storm tracks. Atmospheric teleconnections are distinctively persistent and well developed for these events. For short-duration floods, these coupled patterns are insignificant. A Bayesian network inference model has been developed to quantify these relations and for predicting the likelihood of floods of varying duration using physics informed predictors. We have also introduced an integrated regional flood duration scaling and atmospheric dynamic scaling framework that together enable the coupling of ‘horizontal’ and ‘vertical’ flow of information (e.g., accumulation of streamflow in the basin in the presence of the interrelated land-atmosphere interactions and rainfall episodes) across different space and time scales.

Impact

The consequences of long-term inundation of floodplains, residential and commercial areas and critical infrastructure cannot be fully comprehended without a clear understanding of the variability in the duration of the floods. Furthermore, an improved understanding of the critical forcing of hydrologic systems by meteorological and climatic processes is an essential aspect to factor-in when predicting their functioning and building decision support frameworks to build resilience against natural hazards, especially as adaptive measures are being considered for the future extreme events. The analyses of their causal structure, as shown in this work, will be invaluable for evaluating reservoir and river system operation policies, flood preparation, and hence on the economy and security of the country as critical issues are addressed in this direction.

Summary

We have investigated the governing factors for long‐duration floods with a focus on explaining how flood duration scales with the antecedent flow and atmospheric patterns, which are the primary contributing factors originating from the coupled land‐ocean‐atmosphere dynamic system. We summarized these leading factors as maximum cumulative exceeding flow, blocking systems of pressure in the atmosphere, sufficient amount of moisture supply (water vapor), and the converging process for the available moisture (divergent wind). We also developed a physically based Bayesian network model for inference and prediction of flood duration that allows for a deeper understanding of the nexus of antecedent flow regime, atmospheric blocking, and moisture transport/release mechanisms.

Contact
Naresh Devineni
City University of New York
Publications
Najibi, N, N Devineni, M Lu, and RA Perdigão.  2019.  "Coupled Flow Accumulation and Atmospheric Blocking Govern Flood Duration."  Climate and Atmospheric Science 2(1).  https://doi.org/10.1038/s41612-019-0076-6.