Coupled flow accumulation and atmospheric blocking govern flood duration

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 landatmospheric 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.

A Novel Atmospheric River Identification Algorithm

“…Also, there are some long duration ARSs originate from BOB or AS, then shift eastward, stretch as far as to the eastern North Pacific (Figures a–c). The strong association between the spatial patterns of the AR trajectories and concurrent circulation is consistent with previous findings (Brands et al, ; Jana et al, ; Lu et al, ; Lu & Hao, ; Lu & Lall, ; Najibi et al, ; Najibi et al, ). The varying shapes, orientations, and curvatures of ARs in these examples also emphasize that the smooth AR trajectory is an efficient tool to capture the main spatial pattern of AR pathway and deliver more reliable AR metrics.…”

“…Such a route channels the moisture transport from the warmer oceanic regions in the lower latitude to the midlatitude land areas. Similar channels were also observed in our previous study in other regions, for example, western Europe (Lu et al, 2013), where enhanced moisture transport to the midlatitudes is realized by ARs originate in the tropical Atlantic oceanic areas, and Missouri river basin in the United States (Najibi et al, 2019). In addition, there is a high-pressure system over the western North Pacific, which is consistent with the western North Pacific subtropical high (WNPSH) documented during anomalous moisture allocation and extremes in the EA by Cheng et al (2019), and a low-pressure system over the northern Japan Figure 8.…”

Compound Hot and Dry Events in Europe: Variability and Large-Scale Drivers

“…Atmospheric blocking is defined as a large-scale mid-latitude phenomenon, associated with persistent quasi-stationary high-pressure systems (Barriopedro et al, 2010). Overall, atmospheric blocking exerts significant impacts on different types of extremes such as heatwaves (Della-Marta et al, 2007;Barriopedro et al, 2011;Schubert et al, 2014), droughts (Schubert et al, 2016;, floods (Najibi et al, 2019;Ionita et al, 2020b), and cold spells (Hori et al, 2011;Rimbu et al, 2014). In general, dry and hot summers over Europe are associated with a high frequency of atmospheric blocking centered over the British Isle and/or over Fennoscandia (Della-Marta et al, 2007;Ionita et al, 2017;Bakke et al, 2020;Zhang et al, 2020).…”

East Asia Atmospheric River catalog: Annual Cycle, Transition Mechanism, and Precipitation

“…There is no need to repeat the importance of enhanced moisture transport (e.g., ARs) to regional hydrology as evident by numerous studies in various regions around the world (Cheng et al, 2019;Gorodetskaya et al, 2014;Lu et al, 2013;Lu & Hao, 2017;Lu & Lall, 2017;Najibi et al, 2017Najibi et al, , 2019. Many studies evaluate the contribution of ARs to hydrological events by calculating the fraction of AR-related events (e.g., Nayak & Villarini, 2017;Paltan et al, 2017), but the analysis suffers from its sensitivity to the definitions of AR and AR-related event.…”