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West Africa is subject to climatic variability with a long period of drought during the 1970s–1990s whose impact on groundwater remains poorly studied. This work focuses on the Kou basin in Burkina Faso, which holds a large groundwater resource resulting in exceptional springs. This resource shows signs of depletion that raise a critical question: What is the share of climate and that of withdrawals in the depletion of the resource? To answer this question, we used a hydrogeological model calibrated in steady state and in transient regime (monthly time step 1995–2014; annual time step 1961–2014). The results showed that pumping has a significant impact on the resource, especially in the vicinity of the pumping areas, and caused approximately 30% of the observed decrease in spring discharge. Drought periods and consecutive years without recharge also led to a decrease in groundwater levels. Thus, precipitation deficits and variability, combined with increasing pumping, have endangered the resource.

Conceptual degree-day snow models are often calibrated using runoff observations. This makes the snow models dependent on the rainfall-runoff model they are coupled with. Numerous studies have shown that using Snow Cover Area (SCA) remote sensing observation from MODIS satellites helps to better constrain parameters. The objective of this study was to calibrate the CemaNeige degree-day snow model with SCA and runoff observations. In order to calibrate the snow model with SCA observations, the original CemaNeige SCA formulation was revisited to take into account the hysteresis that exists between SCA and the snow water equivalent (SWE) during the accumulation and melt phases. Several parametrizations of the hysteresis between SWE and SCA were taken from land surface model literature. We showed that they improve the performances of SCA simulation without degrading the river runoff simulation. With this improvement, a new calibration method of the snow model was developed using jointly SCA and runoff observations. Further analysis showed that the CemaNeige calibrated parameter sets are more robust for simulating independent periods than parameter sets obtained from discharge calibration only. Calibrating the snow model using only SCA data gave mixed results, with similar performances as using median parameters from all watersheds calibration.

Explaining the response of catchments with a mix of pervious and impervious surfaces requires the inclusion of controls other than catchment imperviousness. In this study, we made use of a large sample of 70,227 events in 852 U.S. catchments to analyze the interplay of total impervious area (TIA) and antecedent soil moisture (ASM) in determining the event runoff ratio (RR). First, we investigated the importance of TIA as a spatial control compared to other catchment attributes (describing climate and catchment landscape) in explaining the differences between catchments in terms of median event‐scale RR. Second, we examined the importance of ASM as a temporal control of the variability of RR in comparison with spatial settings and event characteristics. Third, events were grouped into 30 classes of TIA and 30 classes of ASM, and linear regression models were used to analyze the evolution of RR depending on each one of the two independent variables. Results showed the following: (1) Analysis of the importance of space‐varying catchment descriptors highlighted the relevance of TIA as a control of catchment response, whereas ASM showed a stronger ability compared to other event characteristics. (2) ASM played a significant role in urbanized catchments as in rural ones. The absence of abrupt changes in the linear model parameters indicates that the impact of urbanization on the relationship between RR and ASM was relatively gradual. (3) Differences in RR between rural and intensively urbanized catchments were observable not only for dry pre‐event conditions but also for wet short‐term conditions. Plain Language Summary: Urbanization causes a substantial increase in surface sealing which leads to dramatic impacts on water cycle. Reliable projections of the impact of urbanization require a good understanding of the multiple factors that shape the response of a catchment along a wide range of urbanization levels. In catchments with a mix of urban and natural areas, the interplay of total impervious area (TIA) and antecedent soil moisture (ASM) conditions is still not well elucidated. To fill this gap, we attempted to quantify the relative importance of TIA and ASM in determining the event‐scale catchment response using a sample of 852 U.S. catchments. We found that both controls play an important role in runoff generation. Particularly, ASM should be considered even in catchments with a high level of urban cover. We also found that the impact of TIA on runoff ratio was relatively gradual and became significant when TIA exceeded 5%. This study provides a solid empirical understanding of the behavior of urbanized catchments, which is a step toward more reliable prediction of the impact of urbanization on hydrology for urban planning policies. Key Points: Runoff ratio was dependent not only on imperviousness but also on antecedent soil moisture conditions, even in highly urbanized catchmentsCatchment imperviousness and antecedent soil moisture had the best ability in explaining the spatiotemporal variability of runoff ratioImpact of total impervious area on runoff ratio became significant when mean catchment imperviousness exceeded 5% [ABSTRACT FROM AUTHOR]

Background: Evaluation of the inferior vena cava (IVC) is not always possible through the subcostal (SC) window. Methods: Inferior vena cava diameters measured by transhepatic (TH) and SC views were compared by Bland and Altman analysis. Results: 131 patients were enrolled, including 88 (67%) under mechanical ventilation. The echogenicity was statistically poorer through the TH view in comparison with the SC view (P =.002). The correlation between the SC and TH views was good and better for respiratory variation than for end‐expiratory or end‐inspiratory diameter measurements (r = 0.86). Despite low bias, the limits of agreement were wide (−7.5 and 7.7 mm for end‐expiratory diameter, −8.7 and 8.5 mm for end‐inspiratory diameter, and −5.3 and 5.8 mm for respiratory variation). Complementary analysis showed that the concordance between the SC and the TH views was better when the IVC was distended. However, the limits of agreement remained broad. Conclusions: Although feasible in almost all patients, the TH view does not provide better echogenicity in comparison with the SC view. Despite a good correlation with the SC view and a low bias, the limits of agreement were wide, especially when the IVC has an ellipsoidal shape, suggesting caution in the interpretation of data obtained by the TH view. [ABSTRACT FROM AUTHOR]

Landscape differences induced by urbanization have prompted hydrologists to define a fuzzy boundary between rural‐ and urban‐specific hydrological models. We addressed the validity of establishing this boundary, by testing two rural models on a large sample of 175 French and United States (US) urbanized catchments, and their 175 rural neighbours. The impact of urbanization on the hydrological behaviour was checked using four metrics. Using a split‐sample test, we have compared the performances, parameter distributions, and internal fluxes of GR4H and IHACRES, two conceptual and continuous models running at the hourly time step. Both model structures are based on soil moisture accounting reservoirs (infiltration, runoff, and actual evapotranspiration) and quick flow/slow flow routing components, with no consideration of any specific feature related to urbanization. Results showed: (a) Except for the ratio of streamflow flashiness to precipitation flashiness, the range of hydrological signature metrics in rural catchments encompassed the specificities of urbanized ones. Overall, the urbanized catchments showed higher ratios of mean streamflow to mean precipitation (median values: 0.39 vs. 0.27) and streamflow flashiness to precipitation flashiness (0.13 vs. 0.03), besides lower baseflow index (0.42 vs. 0.62) and shorter characteristic response time (3 vs. 14 hr). (b) The performances of GR4H revealed no significant distinction between rural and urbanized catchments in terms of Kling–Gupta Efficiency (KGE), whereas IHACRES better simulated urbanized catchments, especially during summer. (c) With respect to differences in urbanization level, the GR4H and IHACRES parameters showed different distributions. The differences in parameters were consistent with the differences in hydrological behaviour, which is promising for a model‐based assessment of the impact of urbanization. (d) The models agreed less in reproducing the internal fluxes over the urbanized catchments than over the rural ones. These results demonstrate the flexibility of conceptual models to handle the specificities of urbanized catchments. [ABSTRACT FROM AUTHOR]

The accuracy of hydraulic models depends on the quality of the bathymetric data they are based on, whatever the scale at which they are applied. The along-stream (longitudinal) and cross-sectional geometry of natural rivers is known to vary at the scale of the hydrographic network (e.g., generally decreasing slope, increasing width in the downstream direction), allowing parameterizations of main cross-sectional parameters with large-scale proxies such as drainage area or bankfull discharge (an approach coined downstream hydraulic geometry, DHG). However, higher-frequency morphological variability (i.e., at river reach scale) is known to occur for many stream types, associated with varying flow conditions along a given reach, such as the alternate bars or the pool–riffle sequences and meanders. To consider this high-frequency variability of the geometry in the hydraulic models, a first step is to design robust methods to characterize the scales at which it occurs. In this paper, we introduce new wavelet analysis tools in the field of geomorphic analysis (namely, wavelet ridge extraction) to identify the pseudo-periodicity of alternating morphological units from a general point of view (focusing on pool–riffle sequences) for six small French rivers. This analysis can be performed on a single variable (univariate case) but also on multiple variables (multivariate case). In this study, we choose a set of four variables describing the flow degrees of freedom: velocity, hydraulic radius, bed shear stress, and a planform descriptor that quantifies the local deviation of the channel from its mean direction. Finally, this method is compared with the bedform differencing technique (BDT), by computing the mean, median, and standard deviation of their longitudinal spacings. The two methods show agreement in the estimation of the wavelength in all reaches except one. The method aims to extract a pseudo-periodicity of the alternating bedforms that allow objective identification of morphological units in a continuous approach with the maintenance of correlations between variables (i.e., at many station hydraulic geometry, AMHG) without the need to define a prior threshold for each variable to characterize the transition from one unit to another. [ABSTRACT FROM AUTHOR]

Calibration of spatially distributed models is an important issue given their over-parameterisation. Three common regionalisation methods can be distinguished: transposition, prescription and constraint. This paper proposes a strategy where the three methods are combined to provide several spatial patterns depending on the model parameters. On the one hand, insensitive and equifinal parameters are prescribed uniformly while parameters with a physical meaning are prescribed at the mesh scale. On the other hand, parameters linked with a proxy runoff signature are constrained over each sub-basin and the remaining parameters are transposed with a physio-climatic pattern constructed over the calibration sub-basins. The above tailor-made pattern regionalisation is applied at the daily time step over two large French catchments, the Loire catchment at Gien covering 35 707 km2 and the Durance catchment at Cadarache covering 11 738 km2. It is then evaluated and compared to a single regionalisation method over dozens of validation stations, treated as ungauged during the parameter regionalisation process. For that purpose, simulated and observed streamflows are compared in light of four runoff signatures: daily runoff, seasonality, flood and low flow. The results show that the tailor-made patterns succeed in significantly enhancing almost all the signatures. The enhancement appears for the least well-modelled stations and contributes a 20% improvement towards gauged modelling. It also tends to guarantee a minimum performance in an ungauged context since the minimum KGE is now 0.4 whatever runoff signature is used. [ABSTRACT FROM AUTHOR]

In hydrology, solving the energy balance could be needed to estimate evapotranspiration or snowmelt. Shortwave (SW) and longwave (LW) incoming radiation fluxes are often derived from climate models or reanalyses. The resolution of these models is often too scarce to reproduce the variability of the energy fluxes in complex topography situations. For hydrological purposes, these radiations can also be simulated using empirical formulations with only maximum and minimum daily air temperature data as inputs. Many different formulations have been developed, mainly for specific areas. In this paper, we modify the existing Bristow atmospheric transmissivity equation so that it can be adapted to different areas and different elevation ranges. A calibration method for the transmissivity equation, coupled to the Sicart emissivity parameterization, has been determined. The new parameterization was developed and validated on a total of 115 meteorological stations from the MeteoSwiss network over the Swiss Alps. The results showed an increase in performances for simulating shortwave radiations in high-elevation areas, without decreasing the performance for lower elevations. However, the performance increase on transmissivity did not improve the longwave simulations as had been expected. The parameterization was also validated on reference surface temperature by solving a simplified energy balance. This makes it possible to evaluate the performance of the two parameterizations combined, considering a typical retro-action of the snow surface. This provided good results with a slight increase in performance compared to the original formulation. It also showed that the inaccuracy of SW radiations has a greater impact on the performance of the reference surface temperature than LW radiation errors. The drawback of this new formulation is that it converges to unexpected parameter values at the calibration process, which requires setting some parameters before calibration. [ABSTRACT FROM AUTHOR]

West Africa experiences great climate variability, as shown by the long-lasting drought since the 1970s. The impacts of the drought on surface water resources are well documented but remain less studied regarding groundwater resources. The nexus between climate variability and groundwater level fluctuations is poorly documented in this area. The present study focuses on the large reserve of groundwater held by the Kou catchment, a tributary of Mouhoun river (formerly the Black Volta) in the southwest of Burkina Faso, in the Sudanian region. Analyses were undertaken using climatic time series (1961--2014), two rivers' hydrometric data (1961--2014), and 21 piezometers' time series (1995--2014) applying statistical trend (Mann--Kendall) and break (Pettitt) tests, correlation analysis, and principal component analysis. The analyses showed that rainfall in the area underwent a significant break in 1970 with an 11%--16% deficit between the period before the break and the period after the break that resulted in a deficit three times greater for both surface and base flows. This significant deficit in flow results from the combined effect of a decrease in rainfall and an increase in evapotranspiration. The response of the catchment to the slight increase in rainfall after 1990 was highly dependent on hydrological processes. At Samendéni, on the Mouhoun River, the flow increased with a slight delay as compared to rainfall, because of the slow response of the base flow. Whereas at Nasso on the Kou river, the flow steadily decreased. The analysis showed that the groundwater level responds to rainfall with a delay. Its response time to seasonal fluctuations ranges from 1 to 4 months and its response time to interannual variations exceeds the timescale of one year. This response is highly dependent on the local aquifer's physical characteristics, which could explain the spatial heterogeneity of the groundwater response. [ABSTRACT FROM AUTHOR]

Copyright of Revista Internacional de Desastres Naturales, Accidentes e Infraestructura Civil is the property of University of Puerto Rico and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Classical morphological descriptors of river networks have been developed in 2D planar system. The third z-dimension (elevation), however, is necessary to model landscape evolution, particularly in a mountainous region when taking into account transport processes such as in glaciology and erosion. This paper aims at analyzing 3D morphometric properties of channel networks on the basis of probabilistic relationships relating the drained area and the elevation. The methodology is an extension of the fundamental planar power-law description proposed by Rodriguez-Iturbe et al. () representing the probability that the drained area A is higher than a threshold area a, P[A > a] ~ a− β, where β is constant and represents an invariant property of natural river networks. A new scaling factor taking into account hypsometry is introduced in the previous power-law relationship, as [ABSTRACT FROM AUTHOR]

Copyright of Hydrological Sciences Journal/Journal des Sciences Hydrologiques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Stochastic flood simulation methods are typically based on a rainfall probabilistic model (used for simulating continuous rainfall series or for estimating probabilities of random rainfall events) and on a rainfall-runoff model. Usually, both of these models are calibrated over observed hydrometeorological series, which may be subject to significant variability and/or nonstationarity over time. The general aim of this study is thus to propose and test a methodology for performing a sensitivity analysis of extreme flood estimations to observed hydrometeorological variability. The methodology consists of performing a set of block-bootstrap experiments: for each experiment, the data used for calibration of a particular model (e.g., the rainfall probabilistic model) is bootstrapped while the model structure and the calibration process are held constant. The SCHADEX extreme flood estimation method has been applied over six catchments located in different regions of the world. The results show first that the variability of observed rainfall hazard has the most significant impact on the extreme flood estimates. Then, consideration of different rainfall-runoff calibration periods generates a significant spread of extreme flood estimated values. Finally, the variability of the catchment saturation hazard has a nonsignificant impact on the extreme flood estimates. An important point raised by this study is the dominating role played by outliers within the observed records for extreme flood estimation. [ABSTRACT FROM AUTHOR]

Classifications of atmospheric circulation patterns are useful tools to improve the description of the climate of a given region and the analysis of meteorological situations. In particular, weather pattern (WP) classifications could be used to improve the description of spatial heavy rainfall. Here, a bottom-up approach, previously used to build WP classification in France, is applied for the definition of a WP classification useful for the description of Austrian heavy rainfall. The optimal spatial extent and the optimal position of the geopotential fields to be taken into account for a WP classification is studied. The proposed WP classification is shown to be coherent with the general knowledge on synoptic situations responsible for heavy rainfall over Austria. Moreover, the classification has good performances in terms of heavy rainfall spatial description compared to 152 COST 733 classifications defined in the same region. In particular, we show that the choice of spatial extent of the geopotential fields, their position and their characteristics is relevant for capturing physical information on synoptic situations responsible for heavy rainfall and that it can improve WP classification performances. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article discusses a study on the sky longwave radiation at Glaciar Zongo in Cordillera Real, Bolivia during the 1999-2000 hydrological year. The temperature and humidity of the atmosphere and the cloud cover are among the factors that influence the sky longwave radiation. The first examination of clear-sky longwave emissivity was conducted at hourly time-steps during daytime. Results showed high clear-sky shortwave transmissivity was due to high altitude and there was minimal variation in air temperature during cloudy periods. The possibility of simulating longwave irradiance at Glaciar Zongo as a function of near-surface air temperature and humidity and of atmospheric transmissivity for solar radiation is highlighted.

Copyright of Hydrological Sciences Journal/Journal des Sciences Hydrologiques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An ultrasonic depth gauge was used to measure snowfall over a 2-year period near the equilibrium line of the Zongo glacier (2.4 km2), Bolivia (16°S). Study of the influence of wind, air temperature, and air moisture on the measurements gives a quantification of snowfall at a 3-hour time step, with a sensitivity of 1 cm of snow. The density of fresh snow is estimated by comparison with rain gauge measurements. The year is marked by a dry season from May to August and a wet season from December to April, during which accumulation and melting coincide on the glacier. Snowfall events are associated with a wind of moderate speed from the valley (less than 4 m s−1). Masses of moist air originate in the Amazon basin. The orographic effect produces precipitation at midday in the Andean valleys and in the afternoon in the high mountains. Nighttime snowfall events occur during periods of bad weather related to the regional atmospheric circulation and last several days. The density of fresh snow is high, about 250 kg m−3, because of the high air temperature during snowfall events (over −3°C). The high snow density and the moderate wind speeds prevent snow drifting conditions, which results in low spatial variability of the accumulation on tropical glaciers. Accurate recording of snowfall at a short time step is important for the study of energy fluxes at the glacier surface because snowfall events greatly increase the albedo and solar radiation is generally the main source of melting energy. [ABSTRACT FROM AUTHOR]

This study investigated the potential of random forest (RF) algorithms for regionalizing the parameters of an hourly hydrological model. The relationships between model parameters and climate/landscape catchment descriptors were multidimensional and exhibited nonlinear features. In this case, machine-learning tools offered the option of efficiently handling such relationships using a large sample of data. The performance of the regionalized model using RF was assessed in comparison with local calibration and two benchmark regionalization approaches. Two catchment sets were considered: (1) A target pseudo-ungauged catchment set was composed of 120 urban ungauged catchments and (2) 2105 gauged American and French catchments were used for constructing the RF. By using pseudo-ungauged urban catchments, we aimed at assessing the potential of the RF to detect the specificities of the urban catchments. Results showed that RF-regionalized models allowed for slightly better streamflow simulations on ungauged sites compared with benchmark regionalization approaches. Yet, constructed RFs were weakly sensitive to the urbanization features of the catchments, which prevents their use in straightforward scenarios of the hydrological impacts of urbanization. [ABSTRACT FROM AUTHOR]

Highlights: [•] δ15N and δ18O allowed characterizing nitrate sources in two karstic springs. [•] Respective endmembers contributions were quantified with Bayesian model. [•] Sp1 is supplied by different endmembers with the same range of proportions. [•] Sp2 is mainly fed by agriculture and chalk nitrates. [Copyright &y& Elsevier]