Recommendations for improving integration in national end-to-end flood forecasting systems: an overview of the FFIR (flooding from intense rainfall) programme

Recent surface-water and flash floods have caused millions of pounds worth of damage in the UK. These events form rapidly and are difficult to predict due to their short-lived and localised nature. The interdisciplinary Flooding From Intense Rainfall (FFIR) programme investigated the feasibility of enhancing the integration of an end-to-end forecasting system for flash and surface-water floods to help increase the lead time for warnings for these events. Here we propose developments to the integration of an operational end-to-end forecasting system based on the findings of the FFIR programme. The suggested developments include methods to improve radar-derived rainfall rates and understanding of the uncertainty in the position of intense rainfall in weather forecasts; the addition of hydraulic modelling components; and novel education techniques to help lead to effective dissemination of flood warnings. We make recommendations for future advances such as research into the propagation of uncertainty throughout the forecast chain. We further propose the creation of closer bonds to the end users to allow for an improved, integrated, end-to-end forecasting system that is easily accessible for users and end users alike, and will ultimately help mitigate the impacts of flooding from intense rainfall by informed and timely action

Représentation des tourbières des hautes latitudes nord dans un modèle de surface : développement d’un schéma hydrologique et estimations des émissions de méthane

Peatlands are widely present in northern latitudes and especiallyin permafrost regions. They contain a high carbon stock and are one ofthe greatest natural sources of methane. Their representation in a climate model is crucial to improve the one of the carbon cycle. Moreover, the contribution of methanepeatland emissions remains uncertain.Methane emissions from peatlands strongly depend on the climate and are influenced primarily by temperature and soil moisture. Meanwhile, climate change is particularlysevere at these latitudes and leads to thawing permafrost with increasing the active layer depth. This large carbon reservoir may be partially mobilized and emitted asCO2 or CH4, depending on hydrological conditions at the surface.The aim of this PhD thesis is to represent northern peatlands in the ORCHIDEE land surface model. This development is carried out in the version of the model that incorporatesprocesses in high latitudes such as the soil freezing. Peatlands are represented by a specific hydrological scheme which improves the exchange of energy and water. The difficulty isbased on the representation of local peatlands processes across a global climate model. Some biological properties were also considered to represent bettervegetation of these environments. To do so, peatlands are integrated as a new type ofvegetation and represented by a fraction of a grid, based on observations. Thehydrological behaviour and the impact of this integration are estimated at the boreal scale as well asregionally. This development then allows estimate changes in the hydrology of peatlands due to global warming. Studying the changes in hydrology of peatlands by the end of th 21st century will improve the prediction of future changes in their CH4 emissions.This development work was then applied to determine the evolution of methane emissions. Peatlands are one of the largest natural sources of methane and control more than 70% interannual variability of atmospheric concentration of CH4. Methane emissions result from various physical and biological processes such as methanogenesis and the methanotrophy. To represent these processes, a flux density model, integratedin ORCHIDEE, was adapted for peatlands to estimate their methane emissions. The evolution of these emissions is studied between the early 20th and late 21st centuries under different climate scenarios.Les tourbières sont largement présentes dans les hautes latitudes nord et plus particulièrement dans les régions de pergélisols. Elles contiennent un important stock de carbone et constituent l’une des plus grandes sources naturelles de méthane. Leur représentation dans un modèle de climat estalors primordiale pour améliorer celle du cycle du carbone. De plus, la contribution des émissions de méthane des tourbières reste encore incertaine et de nombreuses incertitudes persistent. Les émissions de méthane des tourbières dépendent fortement du climat et sont influencées principalement par la température et l’humidité du sol. Parallèlement, le réchauffement climatique particulièrement prononcé à ces latitudes conduit au dégel des pergélisols avec une augmentation de la profondeur de la couche active. Ce grand réservoir de carbone peut être partiellement mobilisé et émis sous forme de CO2 ou CH4, en fonction des conditions hydrologiques à la surface.L’objectif de ces travaux de thèse consiste à représenter les tourbières des hautes latitudes dansle modèle de surface ORCHIDEE. Ce développement est effectué dans la version du modèle qui intègreles processus des hautes latitudes tels que le gel des sols. Les tourbières sont représentées parun schéma hydrologique spécifique ce qui améliore les échanges en énergie et en eau. La difficultérepose sur la représentation des processus locaux des tourbières à l’échelle d’un modèle de climatglobal. Certaines propriétés biologiques ont également été prises en compte afin de mieux représenter la végétation de ces milieux. Pour cela, les tourbières sont intégrées comme un nouveau type devégétation et représentées par une fraction de grille, basée sur des observations. Le comportement hydrologique et l’impact de cette intégration sont évalués à échelle des hautes latitudes ainsi qu’à échelle régionale. Ce développement permet d’estimer ensuite l’évolution de l’hydrologie des tourbières suite au réchauffement climatique. Les changements de l’hydrologie des tourbières d’ici la fin du siècle permettent de mieux évaluer les variations futures de leurs émissions de CH4.Ce travail de développement a ensuite été appliqué pour déterminer l’évolution des émissions deméthane. Les tourbières constituent l’une des plus grandes sources naturelles de méthane et contrôlentà plus de 70 % la variabilité interannuelle de la concentration atmosphérique de CH4. Les émissionsde méthane résultent de différents processus physiques et biologiques tels que la méthanogénèse etla méthanotrophie. Pour représenter ces processus, un modèle de densité de flux existant, intégré dans ORCHIDEE, a été adapté pour les tourbières afin d’estimer les émissions de méthane des tourbières des hautes latitudes. L’évolution de ces émissions est étudiée entre le début du 20ème et la fin du 21ème siècles selon différents scénarios climatiques

Representation of northern peatlands in a surface model : development of a hydrological scheme and estimates of their methane emissions

Les tourbières sont largement présentes dans les hautes latitudes nord et plus particulièrement dans les régions de pergélisols. Elles contiennent un important stock de carbone et constituent l’une des plus grandes sources naturelles de méthane. Leur représentation dans un modèle de climat estalors primordiale pour améliorer celle du cycle du carbone. De plus, la contribution des émissions de méthane des tourbières reste encore incertaine et de nombreuses incertitudes persistent. Les émissions de méthane des tourbières dépendent fortement du climat et sont influencées principalement par la température et l’humidité du sol. Parallèlement, le réchauffement climatique particulièrement prononcé à ces latitudes conduit au dégel des pergélisols avec une augmentation de la profondeur de la couche active. Ce grand réservoir de carbone peut être partiellement mobilisé et émis sous forme de CO2 ou CH4, en fonction des conditions hydrologiques à la surface.L’objectif de ces travaux de thèse consiste à représenter les tourbières des hautes latitudes dansle modèle de surface ORCHIDEE. Ce développement est effectué dans la version du modèle qui intègreles processus des hautes latitudes tels que le gel des sols. Les tourbières sont représentées parun schéma hydrologique spécifique ce qui améliore les échanges en énergie et en eau. La difficultérepose sur la représentation des processus locaux des tourbières à l’échelle d’un modèle de climatglobal. Certaines propriétés biologiques ont également été prises en compte afin de mieux représenter la végétation de ces milieux. Pour cela, les tourbières sont intégrées comme un nouveau type devégétation et représentées par une fraction de grille, basée sur des observations. Le comportement hydrologique et l’impact de cette intégration sont évalués à échelle des hautes latitudes ainsi qu’à échelle régionale. Ce développement permet d’estimer ensuite l’évolution de l’hydrologie des tourbières suite au réchauffement climatique. Les changements de l’hydrologie des tourbières d’ici la fin du siècle permettent de mieux évaluer les variations futures de leurs émissions de CH4.Ce travail de développement a ensuite été appliqué pour déterminer l’évolution des émissions deméthane. Les tourbières constituent l’une des plus grandes sources naturelles de méthane et contrôlentà plus de 70 % la variabilité interannuelle de la concentration atmosphérique de CH4. Les émissionsde méthane résultent de différents processus physiques et biologiques tels que la méthanogénèse etla méthanotrophie. Pour représenter ces processus, un modèle de densité de flux existant, intégré dans ORCHIDEE, a été adapté pour les tourbières afin d’estimer les émissions de méthane des tourbières des hautes latitudes. L’évolution de ces émissions est étudiée entre le début du 20ème et la fin du 21ème siècles selon différents scénarios climatiques.Peatlands are widely present in northern latitudes and especiallyin permafrost regions. They contain a high carbon stock and are one ofthe greatest natural sources of methane. Their representation in a climate model is crucial to improve the one of the carbon cycle. Moreover, the contribution of methanepeatland emissions remains uncertain.Methane emissions from peatlands strongly depend on the climate and are influenced primarily by temperature and soil moisture. Meanwhile, climate change is particularlysevere at these latitudes and leads to thawing permafrost with increasing the active layer depth. This large carbon reservoir may be partially mobilized and emitted asCO2 or CH4, depending on hydrological conditions at the surface.The aim of this PhD thesis is to represent northern peatlands in the ORCHIDEE land surface model. This development is carried out in the version of the model that incorporatesprocesses in high latitudes such as the soil freezing. Peatlands are represented by a specific hydrological scheme which improves the exchange of energy and water. The difficulty isbased on the representation of local peatlands processes across a global climate model. Some biological properties were also considered to represent bettervegetation of these environments. To do so, peatlands are integrated as a new type ofvegetation and represented by a fraction of a grid, based on observations. Thehydrological behaviour and the impact of this integration are estimated at the boreal scale as well asregionally. This development then allows estimate changes in the hydrology of peatlands due to global warming. Studying the changes in hydrology of peatlands by the end of th 21st century will improve the prediction of future changes in their CH4 emissions.This development work was then applied to determine the evolution of methane emissions. Peatlands are one of the largest natural sources of methane and control more than 70% interannual variability of atmospheric concentration of CH4. Methane emissions result from various physical and biological processes such as methanogenesis and the methanotrophy. To represent these processes, a flux density model, integratedin ORCHIDEE, was adapted for peatlands to estimate their methane emissions. The evolution of these emissions is studied between the early 20th and late 21st centuries under different climate scenarios

Implementing northern peatlands in a global land surface model: description and evaluation in the ORCHIDEE high-latitude version model (ORC-HL-PEAT)

International audienceWidely present in boreal regions, peatlands contain large carbon stocks because of their hydrologic properties and high water content, which makes primary productivity exceed decomposition rates. We have enhanced the global land surface model ORCHIDEE by introducing a hydrological representation of northern peatlands. These peatlands are represented as a new plant functional type (PFT) in the model, with specific hydrological properties for peat soil. In this paper, we focus on the representation of the hydrology of northern peatlands and on the evaluation of the hydrological impact of this implementation. A prescribed map based on the inventory of Yu et al. (2010) defines peatlands as a fraction of a grid cell represented as a PFT comparable to C 3 grasses, with adaptations to reproduce shallow roots and higher photosynthesis stress. The treatment of peatland hy-drology differs from that of other vegetation types by the fact that runoff from other soil types is partially directed towards the peatlands (instead of directly to the river network). The evaluation of this implementation was carried out at different spatial and temporal scales, from site evaluation to larger scales such as the watershed scale and the scale of all northern latitudes. The simulated net ecosystem exchanges agree with observations from three FLUXNET sites. Water table positions were generally close to observations, with some exceptions in winter. Compared to other soils, the simulated peat soils have a reduced seasonal variability in water storage. The seasonal cycle of the simulated extent of inundated peatlands is compared to flooded area as estimated from satellite observations. The model is able to represent more than 89.5 % of the flooded areas located in peatland areas, where the modelled extent of inundated peatlands reaches 0.83 × 10 6 km 2. However, the extent of peatlands in northern latitudes is too small to substantially impact the large-scale terrestrial water storage north of 45 • N. Therefore, the inclusion of peatlands has a weak impact on the simulated river discharge rates in boreal regions

Toward Snow Cover Estimation in Mountainous Areas Using Modern Data Assimilation Methods: A Review

International audienceThe snow cover is a key component of land surface hydrology, especially in mountain areas where it governs the amount and timing of water availability in downstream areas. It is involved in relevant climate feedbacks and natural hazards such as avalanches and floods. Monitoring and forecasting snow cover characteristics is challenging. While snow cover extent is relatively easy to retrieve from satellite data, remote sensing retrievals of the snow water equivalent (SWE) is often inaccurate, particularly in complex mountainous terrain. Model-based snow cover estimates, driven by meteorological data, often bear significant uncertainties due to both input data and model errors. Data assimilation can combine both approaches to improve SWE estimates. In this paper, we review current state-of-the-art data assimilation methodologies used to optimally combine measurements with snow cover models in order to reduce uncertainties. The suitability of a given data assimilation method varies with the numerical complexity of snow models as well as the availability and the type of observations. This review describes the issues and challenges associated with data assimilation applied to the mountain snow cover, providing recommendations for existing and upcoming monitoring and prediction systems of snow hydrology in mountainous region

Oceanic forcing of Antarctic climate change: A study using a stretched-grid atmospheric general circulation model

A variable-resolution atmospheric general circulation model (AGCM) is used for climate change projections over the Antarctic. The present-day simulation uses prescribed observed sea-surface conditions, while a set of five simulations for the end of the 21st century (2070-2099) under the SRES-A1B scenario uses sea- surface condition anomalies from selected CMIP3 coupled ocean-atmosphere climate models. Analysis of the results shows that the prescribed sea-surface condition anomalies have a very strong influence on the simulated climate change on the Antarctic continent, largely dominating the direct effect of the prescribed greenhouse gas concentration changes in the AGCM simulations. Complementary simulations with idealized forcings confirm these results. An analysis of circulation changes using self-organizing maps shows that the simulated climate change on regional scales is not principally caused by shifts of the frequencies of the dominant circulation patterns, except for precipitation changes in some coastal regions. The study illustrates that in some respects the use of bias-corrected sea- surface boundary conditions in climate projections with a variable-resolution atmospheric general circulation model has some distinct advantages over the use of limited-area atmospheric circulation models directly forced by generally biased coupled climate model output