Comparaison des réponses du bilan hydrique de bassins situés en Belgique et en Suisse à un changement de climat

Les impacts possibles d'un changement de climat induit par l'augmentation de la concentration des gaz à effet de serre sur le bilan hydrique ont été simulés sur un ensemble de bassins hydrographiques situés en Belgique et en Suisse. Le modèle hydrologique conceptuel IRMB à pas de temps journalier a été utilisé à cette fin et les paramètres du modèle ont été optimisés sur chaque bassin. Les bassins ont une taille comprise entre 100 km2 et 1200 km2 et couvrent des régions de plaine aussi bien que de moyenne montagne. Un même scénario climatique a été adopté pour tous les bassins. Il est principalement caractérisé par une augmentation de la température de près de 3·C et par une légère augmentation des précipitations annuelles. Cette méthodologie a été adoptée afin de montrer les sensibilités respectives des différents termes du bilan hydrique et de les mettre en rapport avec les caractéristiques des bassins étudiés. L'étude s'est focalisée sur l'évolution de l'évapotranspiration et de l'humidité du sol, de l'enneigement, des débits à l'exutoire et des réserves en eau souterraine. Les impacts sont également abordés en termes d'événements extrêmes. Outre des évolutions qui sont prévisibles pour l'ensemble des bassins étudiés, telles une augmentation de l'évapotranspiration, une diminution légère de l'humidité du sol et une réduction de l'enneigement, les réponses de certains termes du bilan hydrique régis par les caractéristiques du sous-sol des bassins peuvent être sensiblement différentes d'une région à une autre. Ainsi, les bassins caractérisés par une infiltration importante subiraient une évolution favorable de leurs réserves en eau souterraine et des débits de base, alors que les bassins où le ruissellement de surface prédomine verraient une diminution se produire. L'altitude des bassins semble aussi jouer un rôle non négligeable. Tous les bassins de plaine présenteraient une augmentation des débits de crues extrêmes, alors que les bassins de moyenne montagne ne subiraient pour ainsi dire pas ces conséquences négatives.By strengthening the so called greenhouse effect, the rise of the atmospheric concentrations of anthropogenic gases, such as CO2, chlorofluorocarbons (CFCs) and methane, will progressively modify the energy budget of the Earth atmosphere and disturb the climate. Temperature at the soil level will rise. Precipitation and air humidity will be modified, inducing a large perturbation of the water cycle and thus of water availability and hydrological extremes. The last International Panel on Climate Change report (IPCC 1994) states that a rise of 0.3 degrees Celsius per decade could be felt in the mean global temperature in the next century. The conclusions of the Second World Climate Conference (1992) pointed out that among the most likely impacts of climate change will be its effects on the hydrological cycle and water management systems. An increase of the incidence of extreme events, such as floods and drought, would cause increased frequency and severity of disasters.The present paper is a synthesis of several separate published and some unpublished climate change impact studies (Bultot et al., 1988 a and b, 1992, 1994; Gellens, 1991; Schädler et al., 1992; Gellens and Demarée, 1993; Gellens and Roulin, 1996) carried out in Belgium and in Switzerland. All these studies have been done with the same hydrological model and the same climate change scenario. This procedure allows a strict comparison of the sensitivity studies and enables us to identify the common responses and the specific behaviour of the catchments. In this latter case, an attempt to identify the geomorphological origin of the particular responses is possible. A set of eight catchments in Belgium and belonging to the Scheldt and Meuse river basins has been studied. These individual catchments cover areas from 100 km2 to 1200 km2 and are spread over the country in order to represent the main catchment types. Precipitation ranges from 730 to 1160 mm per year. In addition, three tributaries of the Rhine river in Switzerland have been selected in the low alpine altitude (lower than 1500 m a.s.l.). Precipitation rates are higher for these three catchments and range from 1080 to 1300 mm. The adopted IRMB (Integrated Runoff Model - Bultot) hydrological model (Bultot et al., 1976 and 1985) is a daily time step conceptual model. It has been designed at the Royal Meteorological Institute of Belgium to simulate the components of the water cycle in medium- sized catchments, i.e. catchments for which the input data, and in particular the precipitation, can be considered as uniform. The main data needed to run the IRMB model are the precipitation and the potential evapotranspiration. This latter variable is assessed by following the procedure described by Bultot et al. (1983) and requires several climatological data, i.e. the net radiation, the air temperature and humidity, the soil temperature at 10, 20 and 50 cm depth and the wind speed at 2 m above the soil. These data are also taken into account in the snow melting- accumulation simulation.The adopted climate scenario has been constructed from the literature in order to combine the results of various simulations produced by different climate models (Bultot et al., 1988b) in a single set of climate increments. The main characteristics of the climate change scenario is a temperature rise reaching some 3 ¡C, with a higher increase in winter than in summer. Precipitation stress consists of a 50 mm yearly rise distributed as a winter rise (about 10 mm) and a slight summer decrease. Although these scenario increments are small in comparison with the year-to-year variability, they are however large enough to reveal the sensitivity of the water balance to climate perturbations. The detailed description of the algorithms used to apply the monthly increments on the daily time step are presented in Bultot et al. (1988b). After a calibration phase for the present climate conditions, a sensitivity analysis of the water balance of the catchments has been carried out by modifying the input data according to the scenario. This well known if - then - what? method gives the sensitivity of the various terms of the water cycle by comparing their values in the present runs and in the disturbed 2xCO2 runs. For practical reasons, the reference periods of the simulation runs are not the same for all the catchments.The study focuses on the evolution of evapotranspiration and soil moisture, of snow cover, of streamflow at the outlet and of groundwater storage. The impacts are also studied in terms of extreme events.For all the catchments, the analysis shows a rise of the evapotranspiration equivalent to some 7 to 10 percent. A small decrease in soil moisture has also been simulated associated with an increase in dry soil days. Due to the temperature rise a strong depletion of the snow cover might be an economically dominant effect in the low alpine regions where winter sport activities represent a large part of the inhabitants' resources. According to the winter precipitation rise, the monthly streamflows in the cold period are also increased under the 2xCO2 conditions.Besides predictable trends common to all the catchments, the study also shows that some components of the water balance governed by the underground characteristics can present uneven responses. Catchments characterized by strong infiltration could be subject to positive evolution of the groundwater storage and of the baseflow, whereas catchments with predominant surface runoff could exhibit the reverse effect. These effects could be important mainly in summer during the low flow period. The altitude of the catchments also seems to be significant. All the lowland catchments present higher extreme streamflows, whereas catchments in low Alpine regions are spared this negative consequence. While a large degree of uncertainty remains in the assessment of the climate in the next century, this study gives a first insight into the direction of the expected climate change impacts. It also points out the need to analyse the sensitivity of catchments with a particular attention to their characteristics

Impact of climate change on hydrological regimes and water resource management in the Rhine basin”,

Abstract. The International Commission for the Hydrology of the Rhine basin (CHR) has carried out a research project to assess the impact of climate change on the river flow conditions in the Rhine basin. Along a bottom-up line, different detailed hydrological models with hourly and daily time steps have been developed for representative sub-catchments of the Rhine basin. Along a topdown line, a water balance model for the entire Rhine basin has been developed, which calculates monthly discharges and which was tested on the scale of the major tributaries of the Rhine. Using this set of models, the effects of climate change on the discharge regime in different parts of the Rhine basin were calculated using the results of UKHI and XCCC GCM-experiments. All models indicate the same trends in the changes: higher winter discharge as a result of intensified snow-melt and increased winter precipitation, and lower summer discharge due to the reduced winter snow storage and an increase of evapotranspiration. When the results are considered in more detail, however, several differences show up. These can firstly be attributed to different physical characteristics of the studied areas, but different spatial and temporal scales used in the modelling and different representations of several hydrological processes (e.g., evapotranspiration, snow melt) are responsible for the differences found as well. Climate change can affect various socio-economic sectors. Higher temperatures may threaten winter tourism in the lower winter sport areas. The hydrological changes will increase flood risk during winter, whilst low flows during summer will adversely affect inland navigation, and reduce water availability for agriculture and industry. Balancing the required actions against economic cost and the existing uncertainties in the climate change scenarios, a policy of 'noregret and flexibility' in water management planning and design is recommended, where anticipatory adaptive measures in response to climate change impacts are undertaken in combination with ongoing activities. Present address

Alternative Splicing of the Cardiac Sodium Channel Creates Multiple Variants of Mutant T1620K Channels

Alternative splicing creates several Nav1.5 transcripts in the mammalian myocardium and in various other tissues including brain, dorsal root ganglia, breast cancer cells as well as neuronal stem cell lines. In total nine Nav1.5 splice variants have been discovered. Four of them, namely Nav1.5a, Nav1.5c, Nav1.5d, and Nav1.5e, generate functional channels in heterologous expression systems. The significance of alternatively spliced transcripts for cardiac excitation, in particular their role in SCN5A channelopathies, is less well understood. In the present study, we systematically investigated electrophysiological properties of mutant T1620K channels in the background of all known functional Nav1.5 splice variants in HEK293 cells. This mutation has been previously associated with two distinct cardiac excitation disorders: with long QT syndrome type 3 (LQT3) and isolated cardiac conduction disease (CCD). When investigating the effect of the T1620K mutation, we noticed similar channel defects in the background of hNav1.5, hNav1.5a, and hNav1.5c. In contrast, the hNav1.5d background produced differential effects: In the mutant channel, some gain-of-function features did not emerge, whereas loss-of-function became more pronounced. In case of hNav1.5e, the neonatal variant of hNav1.5, both the splice variant itself as well as the corresponding mutant channel showed electrophysiological properties that were distinct from the wild-type and mutant reference channels, hNav1.5 and T1620K, respectively. In conclusion, our data show that alternative splicing is a mechanism capable of generating a variety of functionally distinct wild-type and mutant hNav1.5 channels. Thus, the cellular splicing machinery is a potential player affecting genotype-phenotype correlations in SCN5A channelopathies

A Proton Leak Current through the Cardiac Sodium Channel Is Linked to Mixed Arrhythmia and the Dilated Cardiomyopathy Phenotype

Cardiac Na+ channels encoded by the SCN5A gene are essential for initiating heart beats and maintaining a regular heart rhythm. Mutations in these channels have recently been associated with atrial fibrillation, ventricular arrhythmias, conduction disorders, and dilated cardiomyopathy (DCM)

Combining regional approach and data extension procedure for assessing GEV distribution of extreme precipitation in Belgium

The k-day extreme precipitation depths (k=1, 2, 3, 4, 5, 7, 10, 15, 20, 25 and 30) at the climatological network of Belgium (165 stations) are analysed to assess the regional GEV growth curves and to determine the at-site fractiles. The calendar year and the hydrological summer and winter are considered separately. The method proposed combines regional L-moment estimates of the GEV parameters and tends to take advantage of a few long-term well-documented series. Therefore, a data extension procedure based on the fractiles method has been used to extend the 1951-1995 observation period to the 1910-1995 reference period. This ensures the temporal homogeneity of the series by assessing the possible missing extremes and it places all the series in a reference period where the stationarity of the extreme precipitation has been verified. Using the 9 historical series and generating randomly located missing values the efficiency of three data extension methods has been evaluated. This comparison indicates that a procedure using the regional growth curve satisfies this task. It shows that the residual mean square error of the at-site means is reduced when the mean correlation between the reference station and the series presenting gaps exceeds 0.52 but that the corresponding error on high order fractiles is reduced for all the observed correlation and for large numbers (40-50) of missing values. A practical estimation of the confidence intervals is proposed