Impact of climate change on streamflow in selected river basins in Ghana     

Kwabena Kankam-Yeboah  Emmanuel Obuobie  Barnabas Amisigo  Yaw Opoku-Ankomah 《水文科学杂志》2013,58(4):773-788

Abstract

This study uses the Soil and Water Assessment Tool (SWAT) and downscaled climate projections from the ensemble of two global climate models (ECHAM4 and CSIRO) forced by the A1FI greenhouse-gas scenario to estimate the impact of climate change on streamflow in the White Volta and Pra river basins, Ghana. The SWAT model was calibrated for the two basins and subsequently driven by downscaled future climate projections to estimate the streamflow for the 2020s (2006–2035) and 2050s (2036–2075). Relative to the baseline, the mean annual streamflow estimated for the White Volta basin for the 2020s and 2050s showed a decrease of 22 and 50%, respectively. Similarly, the estimated streamflow for the 2020s and 2050s for the Pra basin showed a decrease of 22 and 46%, respectively. These results underscore the need to put in place appropriate adaptation measures to foster resilience to climate change in order to enhance water security within the two basins.

Citation Kankam-Yeboah, K., Obuobie, E., Amisigo, B., and Opoku-Ankomah, Y., 2013. Impact of climate change on streamflow in selected river basins in Ghana. Hydrological Sciences Journal, 58 (4), 773–788.  相似文献   

Determination of the anisotropy of an upper streambed layer in east-central Nebraska, USA   总被引：1，自引：0，他引：1  

Chengpeng Lu  Xunhong Chen  Gengxin Ou  Cheng Cheng  Longcang Shu  Donghui Cheng  Emmanuel Kwame Appiah-Adjei 《Hydrogeology Journal》2012,20(1):93-101

Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (K _v) and horizontal hydraulic conductivity (K _h) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of K _h to K _v from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.  相似文献   

A trigger-tube tracer dilution technique for determining Darcy and apparent velocities of groundwater in dug wells: A case study on phreatic aquiferous formation in Bamenda -Cameroon     

Akoanung Ayaba ABENDONG  ENDENE Emmanuel  Enoh Jeanot FONGOH  AKOACHERE Richard Ayuk II  NJENG Napoleon Ngenge 《地下水科学与工程》2014,7(2):182-194

The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen (18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride (NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy’s groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations.  相似文献   

Velocity and abundance precisions for future high‐resolution spectroscopic surveys: A study for 4MOST     

E. Caffau  A. Koch  L. Sbordone  P. Sartoretti  C.J. Hansen  F. Royer  N. Leclerc  P. Bonifacio  N. Christlieb  H.‐G. Ludwig  E.K. Grebel  R.S. de Jong  C. Chiappini  J. Walcher  S. Mignot  S. Feltzing  M. Cohen  I. Minchev  A. Helmi  T. Piffl  E. Depagne  O. Schnurr 《Astronomische Nachrichten》2013,334(3):197-216

In preparation for future, large‐scale, multi‐object, high‐resolution spectroscopic surveys of the Galaxy, we present a series of tests of the precision in radial velocity and chemical abundances that any such project can achieve at a 4 m class telescope. We briefly discuss a number of science cases that aim at studying the chemo‐dynamical history of the major Galactic components (bulge, thin and thick disks, and halo) – either as a follow‐up to the Gaia mission or on their own merits. Based on a large grid of synthetic spectra that cover the full range in stellar parameters of typical survey targets, we devise an optimal wavelength range and argue for a moderately high‐resolution spectrograph. As a result, the kinematic precision is not limited by any of these factors, but will practically only suffer from systematic effects, easily reaching uncertainties <1km s^–1. Under realistic survey conditions (namely, considering stars brighter than r = 16 mag with reasonable exposure times) we prefer an ideal resolving power of R ∼20 000 on average, for an overall wavelength range (with a common two‐arm spectrograph design) of [395;456.5] nm and [587;673] nm. We show for the first time on a general basis that it is possible to measure chemical abundance ratios to better than 0.1 dex for many species (Fe, Mg, Si, Ca, Ti, Na, Al, V, Cr, Mn, Co, Ni, Y, Ba, Nd, Eu) and to an accuracy of about 0.2 dex for other species such as Zr, La, and Sr. While our feasibility study was explicitly carried out for the 4MOST facility, the results can be readily applied to and used for any other conceptual design study for high‐resolution spectrographs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Development of a User-Centred Web-Mapping Application for Ocean Modellers     

Marta Padilla-Ruiz  Emmanuel Stefanakis  Ian Church 《Marine Geodesy》2013,36(6):507-534

Abstract

This paper reports on the User-Centred Design and development of a web-mapping application from the Ocean Mapping Group (OMG) at the University of New Brunswick (UNB), to deliver ocean mapping data to ocean modellers. First, a work domain analysis was conducted to determine the required application functionality and content, consisting of an ocean modeller informal interview, a competitive analysis, and an online survey. Taking insight from the work domain analysis, a requirements document was prepared to support the development of the first application prototype. This prototype was then evaluated by eight target users, using a cognitive walkthrough and an online survey. The results from this evaluation led to a series of revisions to the functionality, content, and interface of the web-mapping application, establishing the revised prototype. The results showed a useful tool, end-user satisfaction, and stated a wide range of recommendations to enhance functionality for the next steps of the development.  相似文献   

Physical studies of Centaurs and Trans-Neptunian Objects with the Atacama Large Millimeter Array     

Arielle Moullet  Emmanuel Lellouch  Mark Gurwell 《Icarus》2011,213(1):382-392

Once completed, the Atacama Large Millimeter Array (ALMA) will be the most powerful (sub)millimeter interferometer in terms of sensitivity, spatial resolution and imaging. This paper presents the capabilities of ALMA applied to the observation of Centaurs and Trans-Neptunian Objects, and their possible output in terms of physical properties. Realistic simulations were performed to explore the performances of the different frequency bands and array configurations, and several projects are detailed along with their feasibility, their limitations and their possible targets. Determination of diameters and albedos via the radiometric method appears to be possible on ∼500 objects, while sampling of the thermal lightcurve to derive the bodies’ ellipticity could be performed at least 30 bodies that display a significant optical lightcurve. On a limited number of objects, the spatial resolution allows for direct measurement of the size or even surface mapping with a resolution down to 13 milliarcsec. Finally, ALMA could separate members of multiple systems with a separation power comparable to that of the HST. The overall performance of ALMA will make it an invaluable instrument to explore the outer Solar System, complementary to space-based telescopes and spacecrafts.  相似文献   

River profile evolution by plucking in lithologically heterogeneous landscapes: Uniform uplift vs. tilting     

Emmanuel J. Gabet 《地球表面变化过程与地形》2020,45(7):1579-1588

Recent studies provide a theoretical framework for understanding the incision of bedrock rivers by plucking. These studies motivated the development of a numerical model that simulates plucking to explore the evolution of channel profiles in lithologically diverse terrain. In the main governing equation, the incision rate is calculated as a function of the difference between the boundary shear stress and a threshold shear stress needed to entrain blocks from the bed. Because an earlier study suggested that plucking is the primary incisional process in the northern Sierra Nevada (CA), the model was calibrated to approximate the conditions in the region. The profiles of the simulated rivers are stair-stepped, with sharp breaks-in-slope at lithological boundaries. This characteristic is common to rivers draining the northern Sierra Nevada, suggesting that the size of blocks available for plucking, as mediated by the fracture density, may be the primary control on their gradients. Moreover, the numerical experiments highlight the role of threshold shear stresses in the post-orogenic persistence of steep reaches and relict terrain. Finally, comparisons of profiles evolved under tilting or uniform uplift scenarios provide insights into how these different uplift modes affect profile evolution. For example, whereas uniform uplift generates a single migrating knickpoint at the range front, multiple migrating knickpoints can form simultaneously along a river in a tilting landscape. © 2020 John Wiley & Sons, Ltd.  相似文献   

Equatorial symmetry breaking and the loss of dipolarity in rapidly rotating dynamos     

Ferran Garcia  Ludivine Oruba  Emmanuel Dormy 《地球物理与天体物理流体动力学》2017,111(5):380-393

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Restoring Halite Fluid Inclusions as an Accurate Palaeothermometer: Brillouin Thermometry Versus Microthermometry     

Emmanuel Guillerm  Vronique Gardien  Daniel Ariztegui  Frdric Caupin 《Geostandards and Geoanalytical Research》2020,44(2):243-264

Halite traps inclusions of the mother fluid when precipitating. When unchanged, the density of these fluid inclusions (FIs) records the water temperature T_f at the time of crystal formation. As halite is ubiquitous on Earth and geological time, its FIs possess a high potential as temperature archives. However, the use of FIs in halite as an accurate palaeothermometer has been hampered due to limitations of microthermometry, the most commonly used analytical method. Here, we show how Brillouin spectroscopy in halite FIs bypasses these limitations and allows recovering T_f to within 1 °C or less. To demonstrate this, we measured samples synthesised at 24.6 ± 0.5 °C and 33 ± 1 °C, and obtained 24.8 ± 0.4 °C and 31.9 ± 0.4 °C, respectively. This novel approach thus provides an accurate palaeothermometer for lacustrine and marine environments. Moreover, Brillouin spectroscopy solves the long‐standing debate on damage of halite fluid inclusions through quantifying the acceptable temperature excursion for preserving elastic behaviour: [l/(1 µm)]^?0.64 × (90 °C), where l is the FI size. This threshold is lower for FIs close to the surface of the host crystal or to another FI. We also list ‘best practices’ for applying both microthermometry and Brillouin thermometry.  相似文献   

Single-element Anomaly Mapping from Stream Sediment Geochemical Landscapes Aided by Digital Terrain Analysis          下载免费PDF全文

XIANG Jie  XIA Peng  XIAO Keyan  Emmanuel John M. CARRANZA  CHEN Jianping 《《地质学报》英文版》2023,97(1):149-162

The identification of anomalies within stream sediment geochemical data is one of the fastest developing areas in mineral exploration. The various means used to achieve this objective make use of either continuous or discrete field models of stream sediment geochemical data. To map anomalies in a discrete field model of such data, two corrections are required: background correction and downstream dilution correction. Topography and geomorphology are important factors in variations of element con...  相似文献