The diverging trends in annual soil moisture across Europe are stark: Northern regions are increasingly wet, while Southern areas face growing aridity, largely due to contrasting precipitation patterns between these regions. While several studies have examined the consequences of soil moisture deficits and drought in the south, the implications of increasing soil moisture levels in the north remain less explored. This study leverages reanalysis products, such as ERA5-Land, to delve into the soil moisture dynamics of Northern Europe, examining seasonal and sub-seasonal trends across the period 1951-2020. This research includes both a detailed case study of Denmark, and an analysis focusing on the Northern European domain. A primary hypothesis is that spatiotemporal soil moisture trends are influenced not only by changes in mean precipitation, but also by altered temporal patterns of rainfall at sub-seasonal scales across the domain. Moreover, increased soil moisture persistence during the wet season heightens the risk of complex and compound hydro-meteorological interactions between saturated soils and intense rainfall events. The analysis also uncovers a north-to-south soil moisture gradient within Northern Europe, particularly evident with spring drying (MAM). In the southern parts of Northern Europe (including Denmark, southern Sweden, and the Baltic region) this manifests as a wetting trend in winter (DJF) and a drying trend in spring (MAM), posing challenges for water management across sectors. The findings of this study underscore critical research areas requiring further investigation, such as the impacts of increasing soil moisture and more frequent intense rainfall events on streamflow and flooding. Future research could benefit from employing hydrological models to explore these dynamics in greater detail.  

How to cite: Newell, M., Drews, M., Payne, M., and Larsen, M. A. D.: A Northern European paradox: both wetting and drying trends complicate water management , EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-698, https://doi.org/10.5194/ems2024-698, 2024.

There are large uncertainties in the future evolution of water resource availability over western and central Europe. This availability, characterized by total runoff, is the result of two driving variables, precipitation and evapotranspiration. The signal-to-noise ratio for changes in precipitation is low. Changes in evapotranspiration are strongly influenced by uncertainties associated with the modelling of land-atmosphere interactions.

Here we highlight the diverging hydrological behavior of models from the 6^th phase of the Coupled Model Intercomparison Project over western and central Europe. Some models project a marked decrease in runoff in the late 21^st century while others simulate no change or a slight increase. The decrease in runoff is driven either by a decrease in precipitation and evapotranspiration or by an increase in precipitation and an even larger increase in evapotranspiration. The mechanisms responsible for the inter-model spread are investigated with experiments from the Model Intercomparison Project on Land Surface, Snow and Soil Moisture (LS3MIP, van den Hurk et al. 2016) and on the coupled Climate-Carbon Cycle (C4MIP, Jones et al. 2016). The change in large-scale atmospheric circulation is shown to be an important driver of the inter-model spread in precipitation changes in winter. In summer, the physiological effect of CO₂ has a direct influence on evapotranspiration and precipitation changes. Models with a strong biogeochemical effect of CO₂ show a strong decrease in evapotranspiration and precipitation in summer.

The potential relationship between the mean present-day state and trends, and the inter-model spread in the future changes in the hydrological cycle projected by the CMIP6 models is also examined. The models that project a large decrease in runoff are often associated with a large climatological value of evapotranspiration. Among them, some models also show strong positive trends in precipitation and evapotranspiration that are consistent with their future response at the end of the 21^st century. However, it remains difficult to judge the realism of models on the basis of this assessment alone, in particular due to large observational uncertainties.

van den Hurk et al.: LS3MIP (v1.0) contribution to CMIP6: the Land Surface, Snow and Soil moisture Model Intercomparison Project – aims, setup and expected outcome, Geosci. Model Dev., 9, 2809–2832, https://doi.org/10.5194/gmd-9-2809-2016, 2016.

Jones, C. D et al.: C4MIP – The Coupled Climate–Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6, Geosci. Model Dev., 9, 2853–2880, https://doi.org/10.5194/gmd-9-2853-2016, 2016.

How to cite: Deman, J. and Boé, J.: Investigating the large uncertainties in future changes in runoff over western and central Europe, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-174, https://doi.org/10.5194/ems2024-174, 2024.

River routing models are important tools to document, anticipate and forecast river flows dynamic, and perceive the evolution of water resources in the context of climate change. The performance of these models can evolve through different methods, including resolving more complex physical equations, refining the model spatial resolution, improving the model parametrisation, the hydrological network, the forcings. Our study focuses on the impact of more or less complex physical equations and numerical solutions on the performances of the routing model CTRIP.

The CTRIP model (CNRM version of the Total Runoff Integrated Pathways) is the river routing model developed at the CNRM, at Météo France. It converts the runoff simulated by the ISBA (Interaction Sol Biosphère Atmosphère) land surface model into river discharge (http://www.umr-cnrm.fr/spip.php?article1092). It is used for many hydrological applications at medium and large scales. ISBA-CTRIP is the hydrological component of the CNRM climate models, and allows to close the water budget at the global scale. CTRIP handles the horizontal transfer of water over continental surfaces, and describes the main processes of the continental water cycle. In particular, it describes the water propagation into the river network.

Currently, CTRIP simulates the propagation of river discharges using the kinematic approximation of the Saint-Venant equations, in a uniform regime. The equation of water mass conservation is used with the water velocity deduced from Manning's equation. The river is described as a single prognostic reservoir whose discharge is linearly related to the river mass [Decharme 2010]. This simple scheme is adapted to low resolutions, but reaches its limits if the resolution needs to be increased. Going to higher resolutions would allow to better represent dynamic phenomenons, and to take into account small scale processes. It would allow a better representation of the hydrological network, and could result in a quality upgrade for the CNRM hydrological productions. Our study aims to go further the simplistic representation of discharge propagation in rivers into CTRIP and to reach a more complex approach.

In our works, many approximations of the Saint Venant equations are studied : the kinematic approximation in a non uniform regime [Yamazaki 2011], the local inertial approximation [Bates 2010], the diffusive approximation [Moussa 1996], and the dynamic approximation. Several numerical methods are used to solve them : Euler, Crank-Nicholson, Gauss-Seidel. It is coded in CTRIP with a 1/12° spatial resolution (~ 8 km at medium latitudes), in offline mode [Munier 2022] over the Adour basin in South-West of France. CTRIP is forced by total runoffs from the hydrometeorological chain SIM2 (https://www.drias-eau.fr/accompagnement/sections/305) [Le Moigne 2020]. The different versions of the model are compared to a full Saint Venant model, for theorical validation. They are also compared to a dense in-situ network of discharge observations.

How to cite: Peronnet, E., Decharme, B., and Munier, S.: Comparison of numerical solutions for the flow wave propagation in river networks, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-1044, https://doi.org/10.5194/ems2024-1044, 2024.

How to cite: Chen, N., Schlaepfer, D. R., Zhang, L., Lauenroth, W. K., Mi, N., Ji, R., and Zhang, Y.: Evapotranspiration Partitioning using a Process-Based Model over a Rainfed Maize Farmland in Northeast China, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-35, https://doi.org/10.5194/ems2024-35, 2024.

Future climate change is expected to exacerbate hydrological drought in many parts of Europe, making effective management of water resources more imperative to ensure groundwater sustainability. The EU biodiversity strategy for 2030 suggests a strategic target to turn at least 10% of the EU's agricultural areas into high-diversity landscape features like hedges and trees.

In this study, we investigate how afforestation would affect hydrological conditions in Europe under climate change, focusing on three scenarios: (1) a hypothetical extreme scenario transforming all agricultural land into forests under the current climate, (2) a more realistic scenario aligning with the EU biodiversity strategy which envisages converting 10% of the land under the current climate, and (3) a scenario involving the conversion of 10% of agricultural land into forests, but under a climate that is 2°C warmer.

We use the LISFLOOD hydrological model setup across Europe at a spatial resolution of ~2km forced by gridded observed precipitation and temperature over a period of 1991-2020 under current climate. The results were evaluated as changes in evapotranspiration, groundwater levels, and river discharge peaks against a benchmark run. The findings from the afforestation scenario indicated a rise in evapotranspiration, higher groundwater levels, and diminished river flow peaks, suggesting an improvement in water sustainability as well as increased resilience to flooding. This study highlights the hydrological benefits of strategic land use changes, offering key insights for European water resource management and policy formulation in the face of climate change. It also offers a potential toll for decision makers to tackle affects of climate change.

How to cite: Wetterhall, F. and El Garroussi, S.: Data-driven selection of optimal afforestation sites in Europe for drought adaptation , EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-1056, https://doi.org/10.5194/ems2024-1056, 2024.

The intensification of extreme precipitation in a warming climate has been shown in observations and climate models to follow approximately theoretical Clausius-Clapeyron scaling. However, larger changes have been indicated in events of short-duration which frequently trigger flash floods or landslides, causing loss of life. Global analyses of continental-scale convection-permitting climate models (CPCMs) and new observational datasets will be presented that provide the state-of-the-art in understanding changes to extreme weather (rainfall, wind, hail, lightning) and their compounding effects with global warming. These analyses suggest that not only warming, but dynamical circulation changes, are important in the manifestation of change to some types of extreme weather, which must be addressed in the design of new CPCM ensembles. We use our projections to provide the first analyses of impacts on infrastructure systems using a new consequence forecasting framework and show the implications for adaptation. It will be argued that a shift in focus is needed towards examining extreme weather events in the context of their ‘ingredients’ through their evolution in time and space. Coupled with exploration of their causal pathways, sequencing, and compounding effects – ‘storylines’ –, this can be used to improve both early warning systems and projections of extreme weather events for climate adaptation. 

How to cite: Fowler, H.: Rapidly intensifying extreme weather events in a warming world: how important are large-scale dynamics in generating extreme floods?, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-1052, https://doi.org/10.5194/ems2024-1052, 2024.

Flash floods, or rapid response catchment flooding, can be defined at flooding impacts between 0-6 hours of impactful rainfall occurring. Nowcasting can be defined at the 0-2 or 0-6 hour time scale. To save lives, warnings at these very short lead times, whether they are for urban areas or ravines, need to be issued rapidly to a receptive customer base.

The Met Office Expert Weather Hub (formally guidance unit) is operating a surge capacity this summer drawing on rapidly updating diagnostics to identify areas of intense convection and flood producing rainfall, as well as other hazards.

At the same time, the Flood Forecasting Centre (FFC) is piloting a Rapid Flood Guidance Service where days 1 and/or day 2 of the daily Flood Guidance Statement are highlighted as susceptible to rapid flooding. This will highlight potentially affected areas of England and Wales to emergency responders. Using the detailed output from the Expert Weather Hub, the FFC will issue Rapid Flood Guidance to emergency responders at short lead times, less than 6 hours, and possibly less than 2 hours’ notice. 

In addition, the Met Office are running a summer forecasting testbed which will explore two rapid surface water flooding hazard impact models. The Surface Water Flooding Hazard Impact Model, SWFHIM, was developed through the Natural Hazards Partnership and is currently used operationally in the FFC. The second, FOREWARNS, has been developed by the University of Leeds and the Met Office.

This presentation will explain the components of the Rapid Flood Guidance trial and present key findings from research to operations, as well as a summary of the evaluation from the hundreds of emergency responders who have already signed up for the trial. It will also highlight key findings from the evaluation of the surface water impact models, with a focus on less than 24 hours lead time. We will highlight development areas to the science and operational development, and suggest how such short notice warnings can best be communicated to potential users to incite the appropriate actions.

How to cite: Pilling, C., Wynn, A., Turner, R., and Maybee, B.: Rapid Flood Guidance for flash floods – a trial service for England and Wales, summer 2024, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-1105, https://doi.org/10.5194/ems2024-1105, 2024.

Meteorological forecasts are crucial for mitigating extreme weather impacts, but they always contain sources of uncertainty. One of these arises in the prediction of the location of intense convective precipitation systems: this issue is particularly critical for flood forecasting in small watersheds, where even a slight discrepancy in the predicted rainfall location can lead to significant inaccuracies in flow forecasts.

In this study, we propose a methodology for quantifying the spatial biases of rainfall forecasts produced by the MOLOCH meteorological model on the hydraulic node of Milan (northern Italy), which is a strongly urbanized and sensible territory due to the presence of productive activities, critical infrastructures and more than 4 million inhabitants. The goal is to investigate whether the model exhibits “preferential” directions where it tends to misplace convective precipitation events.

A total of 65 significative convective rainfall episodes were selected during the 2013-2022 period, comparing the rainfall forecasts at day+0 with the observed rainfall field obtained through a merging of radar and rain-gauge stations (“PRISMA” dataset, provided by Lombardy Region’s Civil Protection).

The proposed procedure relies on the definition of a domain around the study area which is suitable to define the eastwards/northwards spatial misplacements of the forecast rainfall field, such domain was defined accordingly to an analysis on the Fractional Skill Score (FSS).

Results indicate that the MOLOCH meteorological model tends to misplace convective rainfall systems towards the North-West and North-East directions, and this outcome could be significant to forecasters operating in the civil protection sector, especially for these river catchments with limited spatial extent.

How to cite: Gambini, E., Ravazzani, G., Mancini, M., Valsecchi, I. Q., Cucchi, A., Negretti, A., Davolio, S., and Ceppi, A.: Assessing spatial biases of a meteorological model for real-time flood forecasts in the hydraulic node of Milan, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-911, https://doi.org/10.5194/ems2024-911, 2024.