Abstract
We present 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. Distinct scaling factors at the land surface and regional atmospheric levels are unraveled using this Bayesian network model. Land surface scaling explains the variability in flood duration as a function of cumulative exceedance index, a new measure that represents the evolution of the flood in the basin. Dynamic atmospheric scaling explains the cumulative exceedance index using the interaction between atmospheric blocking system and the synergistic model of wind divergence and atmospheric water vapor. Our findings underline that the synergy between a large persistent low-pressure blocking system and a higher rate of divergent wind often triggers a long-duration flood, even in the presence of moderate moisture supply in the atmosphere. This condition in turn causes an extremely long-duration flood if the basin-wide cumulative flow prior to the flood event was already high. Thus, this new land-atmospheric interaction framework integrates regional flood duration scaling and dynamic atmospheric scaling to enable the coupling of ‘horizontal’ (for example, streamflow accumulation inside the basin) and ‘vertical’ flow of information (for example, interrelated land and ocean-atmosphere interactions), providing an improved understanding of the critical forcing of regional hydroclimatic systems. This Bayesian model approach is applied to the Missouri River Basin, which has the largest system of reservoirs in the United States. Our predictive model can aid in decision support systems for the protection of national infrastructure against long-duration flood events.
Highlights
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.[1,2,3] Analysis of flood frequency is commonly based on the use of instantaneous peak flow; the impacts of floods may not be determined exclusively by its instantaneous peak value.[4]
(see the computation of Qfi in the Methods section). This classification of the flood duration is consistent with the one employed by the Dartmouth Flood Observatory (DFO) for riverine flooding measurements using satellite imagery products.[32]
This long-duration flood scenario may be associated with a high flood peak and can take several days or weeks to recede
Summary
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.[1,2,3] Analysis of flood frequency is commonly based on the use of instantaneous peak flow; the impacts of floods may not be determined exclusively by its instantaneous peak value.[4]. We summarize these leading factors as from oceanic sources and an organized atmospheric blocking system.[16,17] It has been shown recently that synoptic to large-scale atmospheric conditions associated with major flood events seem maximum cumulative exceeding flow (referred to as the cumulative exceedance index, CEI, hereafter), blocking systems of pressure in the atmosphere (anomalous patterns of GPH), to be well correlated with moisture transport from oceanic sources.[18,19] Further, these large-scale atmospheric conditions contribute to anomalous antecedent flow conditions and rainfall intensity.[12] While individual atmospheric rivers (ARs) may not necessarily cause a flood due to the rapid propagation over the basin,[20] a well-established system of atmospheric blocking leads to a stationary weather pattern over a large area, enabling the interaction of the low-level frontal zone with the upper-level tracks This phenomenon is defined as “thunderstorm training at the cyclonic scale” where the atmospheric setup leads to continuous downpours.[21,22] These quasi-stationary synoptic-tolarge-scale tropospheric blocking systems modulate regional climatic features across the mid-latitudes by setting up monotonous weather proxies over the locations under the block and its surroundings.[23] In addition, they regulate the westerly winds by suppressing the eastward progression of extratropical synoptic disturbances.[24] The blocking over the mid-latitudes is linked to a zonal pressure fluctuation mechanism between the Baltic and Greenland, termed Baltic-Greenland Oscillation (BGO). The persistence of regional cyclonic structures locked in-phase by planetary wave blocking, further enhanced by high antecedent soil moisture, has been found[30] to trigger widespread
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