A regional coupled approach to water cycle prediction during winter 2013/14 in the United Kingdom

Huw W Lewis,Simon J Dadson

doi:10.1002/hyp.14438

Huw W Lewis, Simon J Dadson

Open Access

https://doi.org/10.1002/hyp.14438

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Abstract

AbstractA regional coupled approach to water cycle prediction is demonstrated for the 4‐month period from November 2013 to February 2014. This provides the first multi‐component analysis of precipitation, soil moisture, river flow and coastal ocean simulations produced by an atmosphere‐land‐ocean coupled system focussed on the United Kingdom (UK), running with horizontal grid spacing of around 1.5 km across all components. The Unified Model atmosphere component, in which convection is explicitly simulated, reproduces the observed UK rainfall accumulation (r2 of 0.95 for water day accumulation), but there is a notable bias in its spatial distribution—too dry over western upland areas and too wet further east. The JULES land surface model soil moisture state is shown to be in broad agreement with a limited number of cosmic‐ray neutron probe observations. A comparison of observed and simulated river flow shows the coupled system is useful for predicting broad scale features, such as distinguishing high and low flow regions and times during the period of interest but are less accurate than optimized hydrological models. The impact of simulated river discharge on NEMO model simulations of coastal ocean state is explored in the coupled modelling framework, with comparisons provided relative to experiments using climatological river input and no river input around the UK coasts. Results show that the freshwater flux around the UK contributes of order 0.2 psu to the mean surface salinity, and comparisons to profile observations give evidence of an improved vertical structure when applying simulated flows. This study represents the first assessment of the coupled system performance from a hydrological perspective, with priorities for future model developments and challenges for evaluation of such systems discussed.

Highlights

Winter 2013/14 in the United Kingdom (UK) was notable for the cumulative impacts of a series of successive damaging storms crossing north-west Europe (Kendon et al, 2015; Lewis et al, 2015)
Are km-scale regional simulations of precipitation and soil moisture sufficiently accurate to provide useful forcing for distributed modelling of river flows across UK catchments?
The following sub-sections present the characteristics of the simulations of winter 2013/14 relative to available observations, with focus on atmosphere (Section 3.1), land surface (Section 3.2), river flow (Section 3.3), coastal interface (Section 3.4) and near-coastal ocean (Section 3.5) components

Summary

Introduction

Winter 2013/14 in the United Kingdom (UK) was notable for the cumulative impacts of a series of successive damaging storms crossing north-west Europe (Kendon et al, 2015; Lewis et al, 2015). LEWIS AND DADSON sources (Muchan et al, 2015) Such events provide strong motivation for adopting a more holistic approach to understanding and quantifying the risks to populations and infrastructure from compound flooding from multiple sources and from concurrent hazards (Ciurean et al, 2018; Pilling et al, 2016). The coupling or linking of different environmental models has long been considered a necessary approach to achieving this more holistic view. Components would be a representation of the coastal seas, the regional atmosphere and the terrestrial surface and subsurface hydrology that would interact through different boundary conditions.” (reproduced from Beven, 2007)

Results

Discussion

Conclusion