Stochastic Post-Processing of CFSR Daily Precipitation across Canada

Reanalyses, based on numerical weather prediction methods assimilating past observations, provide continuous precipitation datasets and represent interesting options for assessing the climatology of regions with sparse station networks (e.g., northern Canada). However, reanalysis series cannot be used directly because of possible biases and mismatch between their spatial and temporal resolutions with that needed for local applications. To address these issues, a Stochastic Model Output Statistics (SMOS) approach was selected to post-process precipitation series simulated by the Climate Forecast System Reanalysis (CFSR) across Canada. This approach uses CFSR precipitation as a covariate and is based on two regression models: the first one is a logistic regression that deals with precipitation occurrence, and the second is a vector generalized linear model for precipitation intensity. At-site post-processed daily precipitation series are randomly generated using the SMOS approach, and selected climate indicators from the Expert Team on Climate Change Detection and Indices, which is jointly sponsored by the Commission for Climatology of the World Meteorological Organization's (WMO) World Climate Data and Monitoring Programme, the Climate Variability and Predictability Programme of the World Climate Research Programme, and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (CCI/CLIVAR/JCOMM) are estimated and compared with corresponding observed and CFSR values. The two models in the SMOS approach, in addition to adequately correcting systematic biases, produced better predictions than the climatology of the wet and dry and intensity sequences. Additionally, the SMOS generally yields consistent climate indices when compared with those from CFSR without post-processing, though there is still room for improvement for specific indices (e.g., annual maximum of cumulative wet days).     

Slip rate of trench‐parallel normal faulting along the Mejillones Fault (Atacama Fault System): Relationships with the northern Chile subduction and implications for seismic hazards

The recent tectonics of the arid northern Chile Andean western forearc is characterized by trench‐parallel normal faults within the Atacama Fault System (AFS). Since the 1995‐Mw 8.1 Antofagasta earthquake, the mechanism driving this recent and localized extension is considered to be associated with the seismic cycle within the subduction zone. Analyzing morphotectonic patterns along these faults allows examining the seismic potential associated with the subduction zone. Using field Digital Elevation Models and in situ‐produced cosmogenic ¹⁰Be, we determined a 0.2 mm/a long‐term slip rate along the Mejillones Fault, one of the most prominent structures within the AFS. This result suggests that the AFS corresponds to slow slip rate faults despite the rapid subduction context. However, the size of coseismic slips observed along the AFS faults suggests that larger subduction earthquakes (Mw > 8.1) may occur episodically in the area.     

Early modification stage (preresurge) sediment mobilization in the Lockne concentric,marine‐target crater,Sweden

Lockne is a concentric impact structure due to a layered target where weak sediments and seawater covered a crystalline basement. A matrix‐supported, sedimentary breccia is interlayered between the crystalline breccia lens and the resurge deposits in the crater infill. As the breccia is significantly different from the direct impact breccia and the resurge deposit, we propose a separate unit name, Tramsta Breccia, based on the type locality (i.e., the LOC02 drilling at Tramsta). We use granulometry and a novel matrix line‐log method to characterize the sedimentology of the Tramsta Breccia. The obliquity of impact combined with the layered target caused an asymmetric, concentric transient crater, which upon its collapse controlled the deposition of the breccia. On the wide‐brimmed downrange side of the crater where the sedimentary target succession was removed during crater excavation, wide, overturned basement crater ejecta flaps prevented any slumping of exterior sediments. Instead, the sediments most likely originated from the uprange side where the brim was narrow and the basement crater rim was poorly developed, sediment‐rich, and relatively unstable. Here, the water cavity wall remained in closer proximity to the basement crater and, aided by the pressure of the collapsing water wall, unconsolidated black mud would flow back into the crater. The absence of interlayered resurge deposits in the Tramsta Breccia and the evidence for reworking at the contact between the overlying resurge deposits and the Tramsta Breccia indicate that the slumping was a rapid process (<75 s) terminating well before the resurge entered the crater.     

Structures tectoniques et contraintes de cheminement des eaux dans les aquifères karstiques du barrois (Lorraine/Champagne,France)

Résumé

Entre Lorraine et Champagne, dans l’est du Bassin parisien, au contact des calcaires portlandiens du Barrois et des sables et argiles crétacés du Perthois, se développe un karst couvert. Le paysage de côtes est ici perturbé par une tectonique souple (synclinal de Treveray) et cassante (fossé d’effon-drement de la Marne) déterminant l’organisation spatiale des écoulements. En période d’étiage, les méthodes hydrologiques (profils hydrologiques lissés, traçages), permettent de montrer l’influence de cette tectonique d’ondulation et de basculement sur l’écoulement des rivières barroises (Saulx, Marne). Fractures et microfractures influencent la zone de transit vertical des eaux du karst (zone des puits) tandis que les failles compartimentent les aquifères (système du Rupt-du-Puits, 21 km de conduits, 13 km²). Les méthodes d’études hydrologiques, confirment le basculement de la région vers l’ouest déduit des comparaisons de nivellement. © Elsevier, Paris     

The H2020 European Project LiqueFACT

Bulletin of Earthquake Engineering -     

Analyse de sensibilité globale du modèle CATHY aux propriétés hydrodynamiques du sol d’un micro-bassin agricole drainé

Résumé

Une étude d’analyse de sensibilité globale d’une application du modèle hydrologique CATHY (CATchment HYdrology) sur un bassin sous influence de drains agricoles a été réalisée en utilisant les méthodes Morris, FAST99 (Fourier Amplitude Sensitivity Test) et Sobol2002. Ces analyses ont permis d’identifier les paramètres les plus sensibles sur : (a) l’écoulement aux drains et (b) les flux sortant du micro-bassin agricole Bras d’Henri (Québec, Canada). Des 24 paramètres évalués par la méthode de Morris, les neuf et huit paramètres ayant été respectivement très influents sur les deux variables de sortie, ont été analysés par les méthodes FAST99 et Sobol2002. Il s’ensuit que la conductivité hydraulique horizontale à saturation dans les couches sous les drains est la propriété hydrodynamique la plus influente sur les deux variables de sortie. Cette étude démontre que des efforts devraient être portés sur la caractérisation de l’anisotropie du sol, car celle-ci n’est pas à négliger lors d’une modélisation hydrologique tridimensionnelle.

Editeur Z.W. Kundzewicz     

Variation of hydrogeochemical characteristics of water in surface flows,shallow wells,and boreholes in the coastal city of Douala (Cameroon)

ABSTRACT

Groundwater is used by 3?million inhabitants in the coastal urban city of Douala, Cameroon, but comprehensive data are too sparse for it to be managed in a sustainable manner. Hence this study aimed to (1) assess the potability of the groundwater; (2) evaluate the spatial variation of groundwater composition; and (3) assess the interaction and recharge mechanisms of different water bodies. Hydrogeochemical tools and methods revealed the following results in the Wouri and Nkappa formations of the Douala basin, which is beneath Douala city: 30% of water samples from hand-dug wells in the shallow Pleistocene alluvium aquifer were saline and highly mineralized. However, water from boreholes in the deeper (49–92 m depth) Palaeocene aquifer was saline-free, less mineralized and potable. Water in the shallow aquifer (0.5–22 m depth) was of Na⁺-K⁺-Cl^?-NO₃^? type and not potable due to point source pollution, whereas Ca⁺-HCO₃^? unpolluted water dominates in the deeper aquifer. Water in the deep and shallow aquifers indicates the results of preferential flow pass and evaporative recharge, respectively. Possible hydrogeochemical processes include point source pollution, reverse ion exchange, remote recharge areas and mixing of waters with different chemical signatures.

EDITOR D. Koutsoyiannis ASSOCIATE EDITOR M.D. Fidelibus     

Comparison of land surface scheme simulations with field observations versus atmospheric model output as forcing

ABSTRACT

The low density of meteorological stations in parts of Canada necessitates using numerical weather prediction (NWP)/assimilation output for hydrological modelling. In this study, comparisons are made of simulated land surface variables when using field observations versus NWP output as forcing for two well-instrumented sites: the mountainous and forested Marmot Creek Basin (MCRB) in the Canadian Rocky Mountains, and a prairie cropland/grassland site (Kenaston). The Canadian Land Surface Scheme 3.6 (CLASS) was used for modelling. The Global Environmental Multiscale (GEM) model with Canadian Precipitation Analysis (CaPA) was also used as forcing. There was good agreement between observed meteorology and GEM/CaPA, though some deficiencies in GEM/CaPA were identified: the effects of sub-grid topography on incoming radiation and wind speed were not accounted for at MCRB, and CaPA did not capture some convective rainfall events at Kenaston. CLASS simulations using both sets of forcing showed difficulties in simulating snow depth, soil moisture and evapotranspiration; certain difficulties were linked to GEM/CaPA deficiencies and/or CLASS. Both sets of forcing tended to overestimate the duration of snow cover at MCRB, but during different years. With GEM/CaPA as forcing, CLASS overestimated the duration of frozen soils. The GEM/CaPA precipitation difficulties at Kenaston degraded soil moisture simulations.

EDITOR A. Castellarin; ASSOCIATE EDITOR E. Volpi     

Evaluation of satellite-based rainfall products for hydrological modelling in Morocco

ABSTRACT

Several satellite-based precipitation estimates are becoming available at a global scale, providing new possibilities for water resources modelling, particularly in data-sparse regions and developing countries. This work provides a first validation of five different satellite-based precipitation products (TRMM-3B42 v6 and v7, RFE 2.0, PERSIANN-CDR, CMORPH1.0 version 0.x) in the 1785 km² Makhazine catchment (Morocco). Precipitation products are first compared against ground observations. Ten raingauges and four different interpolation methods (inverse distance, nearest neighbour, ordinary kriging and residual kriging with altitude) were used to compute a set of interpolated precipitation reference fields. Second, a parsimonious conceptual hydrological model is considered, with a simulation approach based on the random generation of model parameters drawn from existing parameter set libraries, to compare the different precipitation inputs. The results indicate that (1) all four interpolation methods, except the nearest neighbour approach, give similar and valid precipitation estimates at the catchment scale; (2) among the different satellite-based precipitation estimates verified, the TRMM-3B42 v7 product is the closest to observed precipitation, and (3) despite poor performance at the daily time step when used in the hydrological model, TRMM-3B42 v7 estimates are found adequate to reproduce monthly dynamics of discharge in the catchment. The results provide valuable perspectives for water resources modelling of data-scarce catchments with satellite-based rainfall data in this region.

Editor M.C. Acreman; Associate editor N. Verhoest     

Two Approaches of Textural Classification for the Location of the Flows of Lava on the Volcanic Site of the Mountain Cameroon

Abstract

This study presents two approaches of textural classification on a synthetic aperture radar (SAR) ERS‐2 image, with the aim of the location of the flows of lava and of the serviced zones around the volcanic site of the Mountain Cameroon. The first approach is a method of progressive supervised classification, where a single class is extracted at the same moment, by using 7 parameters of texture stemming from the run length method. Three classes of texture were extracted by this method and the images from the three classes were merged by the red green blue coloured composition to produce the final map. For purposes of comparison, a not supervised classification was applied to the same image. The applied not supervised classification uses parameters of texture stemming from the co‐occurrence matrix method, and it lays on the detection of the peaks of a histogram. The results obtained by the two methods are coherent, and the validation of the results was made by observations during a recent mission on the site of study.