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Summary: Given heightened concerns about climate and human impacts upon hydrology, there is a need to quantify temporal and spatial variability in water availability, and to establish climate–flow associations to predict future water stress. In the UK, most previous climate–river flow research: (1) used single sites or a network of basins with restricted geographical coverage and/or sparse density; (2) included river flow records impacted by anthropogenic influences; (3) generally recognised the importance of basin properties but did not advance beyond broad basin characterisation. This paper addresses these research gaps and aims to improve understanding of seasonal hydroclimatological associations across the UK by: (1) characterising spatial patterns in winter, spring, summer and autumn flows; (2) identifying regions for which atmospheric circulation (AC) and regional climate (RC) drivers exert strongest control on seasonal flows; and (3) identifying basin properties that have a significant influence on seasonal flows. 104 gauged basins covering mainland Great Britain and having near-natural flow records were used to derive four seasonal flow indices for 1975–2005. For each calendar season, cluster analysis was performed on these indices to group hydrologically similar basins. For each resultant class, climate–flow associations were assessed as well as the identification of influential basin physical properties. RC variables were found to have stronger association with seasonal flows than AC with the best RC predictors varying with season. Only winter and summer showed significant AC–flow correlations. Composition of seasonal flow classes reflected not only climatic input but also the physical nature of the basins. A given basin property may have influence for one season, but not for another; and many properties have only limited influence on modifying climate inputs. For both winter and summer seasons, it may be concluded generally that the higher elevation and more impermeable a basin, the stronger the RC–flow association. For AC–flow associations, regions of significant winter correlations match regions of stronger RC–flow association; summer correlations show an eastern shift. This paper illustrates the important (but variable) role of basin properties in modifying climate signals in river flow and the need to consider both sets of controls in evaluating hydrological sensitivity to climate change. [Copyright &y& Elsevier]

Summary: This paper presents a revised procedure for predicting the index flood in ungauged UK catchments based on a revised data-transfer methods. Using annual maximum peak flow data from 602 catchments in the UK, the performance of hydrological regression models linking the (log) index flood to a set of (log) catchment descriptors is investigated and compared to the benefit of enhancing the regression-based estimates with data-transfer from a gauged site that is either (i) geographically close, (ii) considered hydrologically similar, or (iii) both (i) and (ii). The study compares the performance of two regression models when combined with data-transfer: (i) a comprehensive model with four catchment descriptors, (ii) a simple model using only catchment area as an explanatory variable. The results show that the simple regression model benefits more from additional data-transfer than does the more comprehensive model. It is shown that, when data-transfer is included and when the ungauged and the gauged site are extremely close, the two models perform equally well. In cases where the nearest gauged catchment is 1–20km away, data-transfer allows the simpler model to provide predictions which are only moderately worse than those from the comprehensive model, whereas if data-transfer is not used the simpler model is substantially worse than the comprehensive one. Little or no benefit was gained by selecting the gauged site by considering similarity of catchment area. Using data-transfer reduces the spatial correlation in the regression residuals. The results presented in this paper are believed to be of special interest to hydrologists working in regions where only a limited subset of catchments descriptor is routinely made available. [Copyright &y& Elsevier]

Abstract: One of the MOPEX science goals is to develop improved a priori model parameter estimation techniques for both large scale modelling applications and ungauged catchments. The access to daily stream flow data within ungauged catchments is also a central component of many aspects of water resource and water quality management.This paper explores the problem of regionalisation a rainfall-runoff model within the United Kingdom for water resources applications. The results from a regionalisation study using a large dataset of 260 catchments within the United Kingdom are presented.Two approaches to the regionalisation approach are developed and evaluated; a regression-based approach relating model parameters to catchment characteristics and a nearest neighbour based approach. The value of both approaches is evaluated in the context of the quality of the simulations obtained with regionalised parameter sets. The paper identifies that the regression-based approach yields the best predictive results and that these results are encouraging in the context of operational water management. However, the ultimate limitations of the approach are recognised and recommendations are made for further research on nearest neighbour approaches. The paper concludes by raising the question whether the regionalisation of the parameters for prior calibrated model is the most appropriate way to approach the regionalisation question and suggests an alternative modelling framework based on hydrological response units. [Copyright &y& Elsevier]

Abstract: This paper is concerned with mapping monthly precipitation in Great Britain from sparse point data using a range of interpolation methods. The paper applies techniques that make use of the relation between precipitation and secondary variables, such as elevation, and the concern is to assess if they provide more accurate estimates than methods that do not make use of such secondary variables. The techniques applied were: (i) moving window regression (MWR), (ii) inverse distance weighting (IDW); (iii) ordinary kriging (OK), (iv) simple kriging with a locally varying mean (SKlm) and (v) kriging with an external drift (KED). MWR, SKlm and KED make use of secondary information and in this paper elevation data were acquired to inform estimation of precipitation using these techniques. The relationship between precipitation and elevation locally, and its effect on the accuracy of estimates, was examined for each month of 1999. The performance of each interpolation method was assessed through examination of mapped estimates of precipitation and cross-validation. It was concluded that KED provides the most accurate estimates of precipitation for all months from March to December judging by the cross-validation estimation error summary statistics whereas for January and February OK provided the most accurate estimates. [Copyright &y& Elsevier]

Abstract: The paper presents 20-year time series (1975–1994) of annual mass loads discharged from the aggregated freshwater-monitored area of Great Britain for suspended solids, total nitrogen, orthophosphate and zinc. Corresponding time series are also given for regional groups of catchments draining towards five sea-areas recognised for monitoring UK fluvial inputs to the North-East Atlantic. A mass load computational scheme that effectively merges the national river flow and water quality databases is used to derive the mass flow time series, and their utility is considered within the context of strategic information needs and the capabilities of current national monitoring programmes. While the aggregated annual suspended solids loads presented in the paper are often severe underestimates of the actual load, because infrequent sampling tends to miss high concentrations at high flows, the loads for total nitrogen and orthophosphate, which exhibit less variability in concentration than suspended solids, are of a more acceptable quality. Mass loads for zinc, and other determinands often recorded as ‘less than a limit of detection’ (<LOD), can be very uncertain. Bearing in mind the uncertainties involved, the time series presented are assessed for the presence or absence of trends. Not surprisingly, annual loads exhibit correlation with annual runoff. Except for zinc, however, there is no obvious evidence for temporal patterns in the time series that are not associated with variations in annual runoff. Zinc loadings have decreased as a result of improved environmental management in industrialized catchments. Discussion of the sources of uncertainty in regional mass flows is followed by some general recommendations related to capitalising most effectively on available mass flow time series. [Copyright &y& Elsevier]

This paper describes the development of a method that couples flood modelling with network analysis to evaluate the accessibility of city districts by emergency responders during flood events. We integrate numerical modelling of flood inundation with geographical analysis of service areas for the Ambulance Service and the Fire & Rescue Service. The method was demonstrated for two flood events in the City of York, UK to assess the vulnerability of care homes and sheltered accommodation. We determine the feasibility of emergency services gaining access within the statutory 8- and 10-min targets for high-priority, life-threatening incidents 75% of the time, during flood episodes. A hydrodynamic flood inundation model (FloodMap) simulates the 2014 pluvial and 2015 fluvial flood events. Predicted floods (with depth >25 cm and areas >100 m 2 ) were overlain on the road network to identify sites with potentially restricted access. Accessibility of the city to emergency responders during flooding was quantified and mapped using; (i) spatial coverage from individual emergency nodes within the legislated timeframes, and; (ii) response times from individual emergency service nodes to vulnerable care homes and sheltered accommodation under flood and non-flood conditions. Results show that, during the 2015 fluvial flood, the area covered by two of the three Fire & Rescue Service stations reduced by 14% and 39% respectively, while the remaining station needed to increase its coverage by 39%. This amounts to an overall reduction of 6% and 20% for modelled and observed floods respectively. During the 2014 surface water flood, 7 out of 22 care homes (32%) and 15 out of 43 sheltered accommodation nodes (35%) had modelled response times above the 8-min threshold from any Ambulance station. Overall, modelled surface water flooding has a larger spatial footprint than fluvial flood events. Hence, accessibility of emergency services may be impacted differently depending on flood mechanism. Moreover, we expect emergency services to face greater challenges under a changing climate with a growing, more vulnerable population. The methodology developed in this study could be applied to other cities, as well as for scenario-based evaluation of emergency preparedness to support strategic decision making, and in real-time forecasting to guide operational decisions where heavy rainfall lead-time and spatial resolution are sufficient. [ABSTRACT FROM AUTHOR]

Summary: Water companies in the United Kingdom have considered climate change in their water resources plans for more than a decade through studies funded by UK Water Industry Research (UKWIR). This paper presents an initial assessment of the impact of the UK Climate Projections 2009 (UKCP09) on river flows at a national scale for the 2020s under the A1B scenario and the implications for water resource planning. A daily hydrological modelling framework based on two conceptual model structures and the Generalized Likelihood Uncertainty Estimation (GLUE) methodology has been applied to 70 catchments across the UK. A Latin Hypercube Sampling approach was adopted to handle the probabilistic nature of UKCP09. Results show a decrease in mean annual flow over most of the UK, with negative median values of all monthly changes except in winter over the western and northern mountainous areas. Furthermore the results indicate a high likelihood of a significant decline in summer flows. An analysis of variance shows that the main uncertainty in river flow changes comes from the spread in climate projections. Finally results are found to be consistent with a previous UKWIR assessment based on individual projections from 6 Global Climate Models (GCMs) under the A2 scenario. The reduction in summer low-flows, critical for water resources, appears however more limited with UKCP09. Although most expected changes are within natural variability, the drier conditions overall and the greater spread of results with respect to previous assessments indicates a need for testing the robustness of water resource plans. [Copyright &y& Elsevier]

Summary: This paper presents new rainfall and runoff data from a UK green roof test bed which has been collected almost-continuously over a 29-month period from 01/01/2007 to 31/05/2009. Overall, the monitoring period was fairly typical of the location’s long-term climatic averages, although the data set includes some extreme events in June 2007, which were associated with serious flooding locally. To focus on the system’s performance under rainfall events likely to be of interest from an urban drainage/stormwater management perspective, return period analysis has been applied to identify those storm events with a rainfall depth in excess of 5mm and a return period greater than one year. According to these criteria, 22 significant events have been identified, of which 21 have reliable runoff records. Overall the roof provided 50.2% cumulative annual rainfall retention, with a total volumetric retention equivalent to 30% during the significant events. The annual performance figures are towards the lower end of a range of international data, probably reflecting the fact that rainfall depths may be higher and evapotranspiration rates lower than in some more continental climatic settings. The roof’s finite retention depth means that the maximum possible retention percentage declines as storm depth increases, and retention varied from between 0 and 20mm, or 0% to 100%. Although some attenuation and delay of peak runoff is generally observed (mean peak flow reduction of 60% for the 21 significant events), the irregularity of natural rainfall patterns, combined with the variable influence of detention storage in specific events, makes the identification of peak-to-peak lag times difficult and arguably meaningless. Regression analyses have been undertaken to explore the potential to predict the roof’s hydrological performance as a function of storm characteristics. However, these are shown to have poor predictive capability, even for the system from which they were derived. Through a detailed examination of data from three contrasting events, it is argued that the inter-event processes are too complex to be captured by this type of modelling approach. Instead, an understanding of the hydrological processes affecting the flux of moisture into and out of the substrate is required to explain the observed runoff response. Locally-derived evapotranspiration rates and the roof’s observed maximum retention capacity are utilised to provide pragmatic guidance on the retention performance to be expected in response to selected design events. [ABSTRACT FROM AUTHOR]

Summary: This paper compares the fluvial flux of nitrate at the UK’s tidal limit with an estimate of losses from the terrestrial biosphere at the point of entry to the river system to estimate in-stream losses across the UK’s entire river network between 1925 and 2007. These estimates were used to support interpretation of the current trend in the fluvial flux of nitrogen from the UK, and to give an assessment of the fluvial component of the total nitrogen budget of UK. The release of nitrate to the point at which it enters the stream network is estimated, using a Monte-Carlo framework, from a description of annual soil N mineralisation and immobilisation combined with an export coefficient model. Long-term records of land use (including – agricultural, forestry and urban uses); livestock; human population and atmospheric deposition are used. The study shows that: [(i)] The flux of nitrate from UK soils in the period since 1925 varied between 420 and 1463ktonnesNyr−1, with two peaks, one in 1944 and one in 1967. The first of these peaks was caused by mineralisation of soil organic matter following radical land use change in the 1940s, and the second was a multifactorial response to land use change and agricultural intensification in the 1960s. [(ii)] The current trend in N release from soils appears to be downward but the current fluvial flux at the tidal limit is slowly increasing. It is possible that in the near future nitrate–N losses at the tidal limit will, in some years, exceed N losses from soils implying a net N gain into the fluvial network. This apparent gain can be explained by the breakthrough of high nitrate groundwater into surface waters. [(iii)] The predicted export from UK soils at source as water enters the stream network implies that the UK will soon become a net source of total reactive N species, as the capacity for in-stream removal becomes exhausted by the ingress of N-rich groundwater to the river system. [ABSTRACT FROM AUTHOR]

Summary: Understanding hydrological flow pathways is important for modelling stream response, in order to address a range of environmental problems such as flood prediction, prediction of chemical loads and identification of contaminant pathways for subsequent remediation. This paper describes the use of parametrically efficient, low order models to identify the dominant modes of stream response for catchments within the Upper Eden, UK. A first order linear model adequately identified the dominant mode in all but one of the sub-catchments. A consistent pattern of time constants and pure time delays between catchments was observed over different periods of data. In the nested catchments, time constants increased as the catchment size increased from 1.1km2 at Gais Gill (2–7h) to 69.4km2 at Kirkby Stephen (5–10h) to 223.4km2 at Great Musgrave (7–16h) to 616.4km2 at Temple Sowerby (11–22h), but Blind Beck (a small catchment 8.8km2, time constants 11–21h) had time constants most similar to Temple Sowerby. This was attributed to a combination of the storage role of permeable rock strata, where present, and the effect of scale on sub-surface and channel routing. A first order model could not be identified for the 1.0km2 Low Hall catchment, which comprises permeable sandstone overlain by Quaternary sediments. A second-order model of Low Hall stream showed a higher proportion of water taking a slower pathway (76% via a slow pathway; time constant 252h) than a model with the same structure for the 8.8km2 Blind Beck (46% via slow pathway; time constant 60h), where only 38% of the basin was underlain by the same permeable sandstone. This highlights the need to quantify the role of deep pathways through permeable rock, where present, in addition to the effect of catchment size on response times. [Copyright &y& Elsevier]

Summary: Projections of climate for the 2080s from an ensemble of global climate models (GCMs) run under a medium–high (A2) emissions scenario are used to simulate changes in groundwater resources of a Chalk aquifer in central-southern England. Few studies that have investigated the impacts of climate change on groundwater resources have addressed uncertainty. In this paper the uncertainty associated with use of a suite of GCM outputs in catchment scale impact studies is quantified. A range of predictions is obtained by applying precipitation and temperature change factors, derived from thirteen GCMs, to a distributed recharge model and a groundwater flow model of the Chalk aquifer of the Marlborough and Berkshire Downs and south-west Chilterns in the UK. The ensemble average suggests there will be a 4.9% reduction in annual potential groundwater recharge across the study area, although this is not statistically significant at the 95% confidence level. The spread of results for simulated changes in annual potential groundwater recharge range from a 26% decrease to a 31% increase by the 2080s, with ten predicting a decrease and three an increase. Whilst annual recharge is not found to change significantly, the multi-model results suggest that the seasonal variation in the groundwater resource will be greater, with higher recharge rates during a reduced period of time in winter. The spread of predictions for changes in river baseflow, at the bottom of the largest river sub-catchment, is from −16 to +33% in March and from −68 to −56% in October. The effects of climate change are shown to depend significantly on the type of land-use. It is concluded that further research is required to quantify the effect of different vegetation types on Chalk covered by different thicknesses of soil and their response to a changing climate. [Copyright &y& Elsevier]

Summary: Investigation of links between large-scale climate and river basin-scale precipitation and discharge is necessary to improve understanding of the hydroclimatological process chain. This paper aims to identify the large-scale circulation variables that yield significant statistical relationships with precipitation and river flow for ten British basins, and evaluate the dependence of the strength and location of centres of climate–hydrology correlation on basin situation. Using quasi-geostrophic theory as a framework to select appropriate explanatory variables, this study undertakes ranked correlation analysis between gridded ERA-40 atmospheric data and precipitation and river flow observations at a monthly resolution over a 26year period. Relationships between large-scale atmospheric circulation and precipitation and river flow are found to vary spatially and seasonally across Britain, with strongest associations evident in western Britain and in winter. Monthly precipitation totals and river flow demonstrate highly significant negative (positive) correlation with mean sea level pressure MSLP (Zonal Wind U), but the location of high correlation centres vary for different basins. There are weaker atmospheric links with river flow compared to precipitation, reflecting the non-linearity of the rainfall–runoff transformation and the importance of basin properties as a modifier of climate inputs. The North Atlantic Oscillation Index (NAOI) cannot capture the seasonal movement of climate–hydrology connections due to the fixed station locations used for the index calculation, and thus has weaker monthly correlations with precipitation and river flow compared to gridded ERA-40 circulation variables (and in particular the comparable MSLP). [ABSTRACT FROM AUTHOR]

Summary: This paper develops tools to assess regional drought events based on limited periods of record and applies them to regional climate model output to examine potential future changes in drought due to increased greenhouse gases. The drought metric was defined as a monthly time series of standardized 12-month precipitation accumulations. Regional drought events were characterised by determining the severity, area, duration and frequency of dry periods. In order to improve statistical inference of drought events, a drought generator was adopted to synthesis a large number of events trained on the available data. In nearly all cases, the drought generator produces synthetic events with drought characteristics statistically indistinguishable from the training data. Severity–Area–Frequency (SAF) curves and Area–Probability (Area–P) curves could then be constructed from the synthetic data to determine the return period of a drought event of a given severity covering a given area. These techniques were applied to observations and to output from the Hadley Centre regional climate model (HadRM3). HadRM3, when driven by climate reanalysis data, has good correlation with the observed drought metric. HadRM3 also captures the timing of observed dry periods but not the relative seriousness of any particular period. Natural variability is large with regional drought characteristics highly dependent on the time period covered by the training data. Although the synthetic drought characteristics of HadRM3 generally overlap with the observed natural variability; the model slightly overestimates the area of observed drought; underestimate its frequency; and underestimate the severity at any given area. HadRM3 projections of changes in drought characteristics over the second half of the 21st century under increased atmospheric greenhouse gases hint at an increase in the severity of drought. However, any changes are not readily distinguishable from natural variability or projection uncertainty. Therefore it is not yet possible to robustly predict changes in UK meteorological droughts arising from increased greenhouse gasses. [Copyright &y& Elsevier]

Summary: This paper presents a novel framework for undertaking climate change impact studies, which can be used for testing the robustness of precautionary climate change allowances used in engineering design. It is illustrated with respect to fluvial flood risk in the UK. The methodology departs from conventional scenario-led impact studies because it is based on sensitivity analyses of catchment responses to a plausible range of climate changes (rather than the time-varying outcome of individual scenarios), making it scenario-neutral. The method involves separating the climate change projections (the hazard) from the catchment responsiveness (the vulnerability) expressed as changes in peak flows. By combining current understanding of likelihood of the climate change hazard with knowledge of the sensitivity of a given catchment, it is possible to evaluate the fraction of climate model projections that would not be accommodated by specified safety margins. This enables rapid appraisal of existing or new precautionary allowances for a set of climate change projections, but also for any new set of climate change projections for example arising from a new generation of climate models as soon as they are available, or when focusing on a different planning time horizon, without the need for undertaking a new climate change impact analysis with the new scenarios. The approach is demonstrated via an assessment of the UK Government’s 20% allowance for climate change applied in two contrasting catchments. In these exemplars, the allowance defends against the majority of sampled climate projections for the 2080s from the IPCC-AR4 GCM and UKCP09 RCM runs but it is still possible to identify a sub-set of regional scenarios that would exceed the 20% threshold. [ABSTRACT FROM AUTHOR]

Summary: Flood inundation modelling on urbanised floodplains has become more feasible due to the increased availability of high resolution digital terrain data and computer power. However, studies that validate simulations with spatially distributed measurements are rare, especially for large events. This paper reports one of the most comprehensive validation data sets available to date on an urban flood, collected in January 2005 after a major event in the city of Carlisle, UK. For the first time this case study collated distributed urban maximum water level and extent measurements with gauged hydrographs, LiDAR elevation data and digital Mastermap® data. These data were used to build and calibrate two 2D diffusion wave models at the whole city scale, based on digital elevation data with and without buildings. RMSE between measured and simulated maximum water level was 0.32m and 0.28m for the models with and without buildings, respectively, the latter being more accurate due to blockages on the floodplain when building heights were included in the topography. The magnitude of simulation errors compared well with other studies in the literature, and considering potential errors in the measurement data indicates that the diffusion wave approach was adequate to capture the first-order physics relevant here, although a global channel roughness parameter was unable to capture the full spatially-varying dynamics of the flood event. [Copyright &y& Elsevier]

Summary: This paper presents a methodology to calibrate hydraulic models using possibility of inundation maps derived from satellite imagery. The study was performed on a river reach of the Lower Dee, UK, where a coarse resolution image (ENVISAT ASAR) and high resolution satellite image (ERS-2 SAR) were acquired at the same time during the December 2006 flood event. Ten different flood extent maps were derived from the two flood images by using five different procedures to process these data. These flood extent maps were used to perform a sensitivity analysis of a simple raster-based inundation model (LISFLOOD-FP). The sensitivity analysis enabled us to investigate the capability of the two different resolution images to calibrate the friction parameters of the flood inundation model. The analysis showed that the optimal parameters of the model depend on the type of satellite image used to evaluate the model as well as on the particular procedure used to derive the flood extent map. Finally, the study developed a novel methodology to calibrate flood inundation models by comparing the model results to a possibility of inundation map obtained by combining the ten different flood extent maps. [Copyright &y& Elsevier]

Summary: In this paper, we use an airborne synthetic aperture radar to map river flood inundation synoptically at fine spatial resolution (1.2m) along a ∼16km reach of the River Severn, west-central England. Images were obtained at four times through a large flood event between 8th and 17th November 2000 and processed using a statistical active contour algorithm to yield the flood shoreline at each time. Intersection of these data with a high vertical accuracy survey of floodplain topography obtained from airborne laser altimetry permitted the calculation of dynamic changes in inundated area, total reach storage and rates of reach dewatering. In addition, comparison of the data to gauged flow rates, the measured floodplain topography and map data giving the location of embankments and drainage channels on the floodplain yields new insights into the factors controlling the development of inundation patterns at a variety of scales. Finally, the data were used to assess the performance of a simple two-dimensional flood inundation model, LISFLOOD-FP, and allows us, for the first time, to validate the dynamic performance of the model. This process is shown to give new information into structural weaknesses of the model and suggests possible future developments, including the incorporation of a better description of floodplain hydrological processes in the hydraulic model to represent more accurately the dewatering of the floodplain. [Copyright &y& Elsevier]

This paper describes the simulation of a succession of annual hydro-periods describing water table variations in a British floodplain wetland, Narborough Bog. This is achieved through the application of a model, developed using MODFLOW, which requires inputs of weekly precipitation, evapotranspiration and river stage. The model reproduces the observed temporal variation in the wetland water tables illustrating the range in water table conditions experienced by the wetland, their relationship to hydrometeorological conditions, and the seasonal and annual variability in the wetland water budget. The model also estimates defuse water fluxes such as seepage flows to and from the adjacent river. The model simulations demonstrate the importance of successful representation of the stratigraphy of alluvial and organic deposits within the wetland. Model performance is evaluated for 2 years: 1991 and 1992 during a period of field instrumentation. The model is then used to reproduce the wetland hydroperiod for further 6 years: 1979, 1980, 1982, 1983, 1987 and 1988 when local data for precipitation, evapotranspiration and river stage are available. The results indicate how the wetland responds to a combination of hydrological events and emphasise the importance of precipitation—both weekly totals and its annual distribution. The model simulations reveal the importance of the water storage function of the wetland and indicate the varying relationship of the wetland to the lowland river: at low flows the river represents a base level to which the wetland water table grades. Conversely, for small periods of time wetland water tables are elevated by the effects of a marginal silt–clay levee adjacent to the riverbank. Conditions of influent seepage from river to wetland were experienced only on isolated occasions. Such results demonstrate the benefits of floodplain wetlands in moderating extremes of river flow and demonstrating the need for rivers and floodplain wetlands to remain closely integrated. [Copyright &y& Elsevier]

• Second-order discontinuous Galerkin (DG2) flood model is compared to FV-based industrial models. • Variants of the DG2 model are explored with and without local slope limiting. • DG2 shows superior resistance to numerical diffusions leading to better momentum conservations. • The DG2 variant with no slope limiter outperforms for flows that are typical of flood inundation. • DG2 produces more accurate hydrographs in certain scenarios and/or on coarser grids. Finite volume (FV) numerical solvers of the two-dimensional shallow water equations are core to industry-standard flood models. The second-order Discontinuous Galerkin (DG2) alternative, although a viable way forward to improve current FV-based flood models, is yet under-studied and rarely used to support flood modelling applications. This paper systematically explores and compares the predictive properties of a robust DG2 flood model to those of prominent FV-based industrial flood models. To identify the simplest and most efficient DG2 configuration suitable for flood inundation modelling, two variants – with and without local slope limiting – are considered. The numerical conservation properties of the DG2 variants are compared to those of a first-order FV (FV1) and a second-order FV (FV2) counterparts. The DG2 variants are then tested over five realistic flooding scenarios, recommended by the UK Environment Agency to validate 2D flood model capabilities, while comparing their performance against that of four FV-based commercial models (i.e. TUFLOW-FV1, TUFLOW-FV2, TUFLOW-HPC and Infoworks ICM). Results reveal that the DG2 variant without local limiting (DG2-NL) is capable to simulate shockless flood flows featured in a wide range of flood modelling applications. The DG2-NL shows closer predictions to commercial model outputs at twice-coarser spatial resolution, and can run twice faster to produce more informative hydrograph with small-scale transients over long-range simulations, even when the sampling is far away from the flooding source. [ABSTRACT FROM AUTHOR]