Investigating coastal backwater effects and flooding in the coastal zone using a global river transport model on an unstructured mesh

[摘要] Coastal backwater effects are caused by the downstreamwater level increase as a result of elevated sea level, high riverdischarge and their compounding influence. Such effects have crucial impactson floods in densely populated regions but have not been well represented inlarge-scale river models used in Earth system models (ESMs), partly due tomodel mesh deficiency and oversimplifications of river hydrodynamics. Usingtwo mid-Atlantic river basins as a testbed, we perform the first attempt tosimulate the backwater effects comprehensively over a coastal region usingthe MOSART river transport model under an ESM framework, i.e.,Energy Exascale Earth System Model (E3SM) configured on a regionally refinedunstructured mesh, with a focus on understanding the backwater drivers andtheir long-term variations. By including sea level variations at the riverdownstream boundary, the model performance in capturing backwaters isgreatly improved. We also propose a new flood event selection scheme tofacilitate the decomposition of backwater drivers into different components.Our results show that while storm surge is a key driver, the influence ofextreme discharge cannot be neglected, particularly when the river drains toa narrow river-like estuary. Compound flooding, while not necessarilyincreasing the flood peaks, exacerbates the flood risk by extending theduration of multiple coastal and fluvial processes. Furthermore, oursimulations and analysis highlight the increasing strength of backwatereffects due to sea level rise and more frequent storm surge during1990–2019. Thus, backwaters need to be properly represented in ESMs toimprove the predictive understanding of coastal flooding.

[学科分类] 妇产科学