Entity

Time filter

Source Type

Skipton, United Kingdom

Forsythe N.,Newcastle University | Hardy A.J.,Aberystwyth University | Fowler H.J.,Newcastle University | Blenkinsop S.,Newcastle University | And 3 more authors.
Journal of Climate | Year: 2015

Clouds play a key role in hydroclimatological variability by modulating the surface energy balance and air temperature. This study utilizes MODIS cloud cover data, with corroboration from global meteorological reanalysis (ERA-Interim) cloud estimates, to describe a cloud climatology for the upper Indus River basin. It has specific focus on tributary catchments in the northwest of the region, which contribute a large fraction of basin annual runoff, including 65% of flow originating above Besham, Pakistan or 50 km3 yr-1 in absolute terms. In this region there is substantial cloud cover throughout the year, with spatial means of 50%-80% depending on the season. The annual cycles of catchment spatial mean daytime and nighttime cloud cover fraction are very similar. This regional diurnal homogeneity belies substantial spatial variability, particularly along seasonally varying vertical profiles (based on surface elevation). Correlations between local near-surface air temperature observations and MODIS cloud cover fraction confirm the strong linkages between local atmospheric conditions and near-surface climate variability. These correlations are interpreted in terms of seasonal and diurnal variations in apparent cloud radiative effect and its influence on near-surface air temperature in the region. The potential role of cloud radiative effect in recognized seasonally and diurnally asymmetrical temperature trends over recent decades is also assessed by relating these locally observed trends to ERA-Interim-derived trends in cloud cover fraction. Specifically, reduction in nighttime cloud cover fraction relative to daytime conditions over recent decades appears to provide a plausible physical mechanismfor the observed nighttime cooling of surface air temperature in summermonths. © 2015 American Meteorological Society. Source


Bendall B.,Lowestoft Laboratory | Moore A.,Lowestoft Laboratory | Maxwell D.,Lowestoft Laboratory | Davison P.,Lowestoft Laboratory | And 6 more authors.
Fisheries Management and Ecology | Year: 2012

Advances the field of telemetry techniques during the last few decades have greatly expanded our knowledge on migratory behaviour and provided the opportunity to obtapractically useful data for the conservation and management of salmonid populations. However, applying this information to the development of much needed population-based migration models has been limited. Furthermore, this research has generally been restricted to assessing the role of river flow on fish movement. Models derived from a 6-year telemetry study on the movements of Atlantic salmon, Salmo salar L., and sea trout, Salmo trutta L., the River Tyne are presented together with an assessment of counter data from the same river to highlight the importance of additional environmental and physiological parameters regulating fish movement. The data are discussed relation to the advantages of telemetry data, the need to develop predictive models, the statistical methods used and the potential direction of future work this area. © 2011 Crown copyright. Source


Archer D.R.,JBA Consulting Engineers and Scientists | Climent-Soler D.,Cranfield University | Holman I.P.,Cranfield University
Hydrology Research | Year: 2010

Despite substantial evidence that land use and management can enhance flood runoff at a local scale, evidence of increased flood risk based on peak discharges is lacking in catchments greater than 10 km2. This analysis is instead based on assessing changes in short-term rates of change in discharge. The influence of land use is demonstrated first on the small Coalburn catchment where changes in rates of rise are closely related to drainage and afforestation. For the larger Axe catchment (288 km2), changes in rates of rise are investigated by comparing annual maximum and peaks over a threshold flows for different periods, by comparing rates of rise associated with given daily rainfall and by adapting the method of flow variability analysis for use of rates of change rather than flow itself. All these methods demonstrate significant changes in river flow dynamics which seem to be in parallel with land use changes even when the influence of climate variability from year to year has been taken into account. Rates of change in discharge appear to respond to land use changes and thus provide a potential basis for application to land use management policies. © IWA Publishing 2010. Source


Forsythe N.,Newcastle University | Fowler H.J.,Newcastle University | Blenkinsop S.,Newcastle University | Burton A.,Newcastle University | And 4 more authors.
Journal of Hydrology | Year: 2014

Assessing local climate change impacts requires downscaling from Global Climate Model simulations. Here, a stochastic rainfall model (RainSim) combined with a rainfall conditioned weather generator (CRU WG) have been successfully applied in a semi-arid mountain climate, for part of the Upper Indus Basin (UIB), for point stations at a daily time-step to explore climate change impacts. Validation of the simulated time-series against observations (1961-1990) demonstrated the models' skill in reproducing climatological means of core variables with monthly RMSE of <2.0. mm for precipitation and ≤0.4. °C for mean temperature and daily temperature range. This level of performance is impressive given complexity of climate processes operating in this mountainous context at the boundary between monsoonal and mid-latitude (westerly) weather systems. Of equal importance the model captures well the observed interannual variability as quantified by the first and last decile of 30-year climatic periods.Differences between a control (1961-1990) and future (2071-2100) regional climate model (RCM) time-slice experiment were then used to provide change factors which could be applied within the rainfall and weather models to produce perturbed 'future' weather time-series. These project year-round increases in precipitation (maximum seasonal mean change:+27%, annual mean change: +18%) with increased intensity in the wettest months (February, March, April) and year-round increases in mean temperature (annual mean +4.8. °C). Climatic constraints on the productivity of natural resource-dependent systems were also assessed using relevant indices from the European Climate Assessment (ECA) and indicate potential future risk to water resources and local agriculture.However, the uniformity of projected temperature increases is in stark contrast to recent seasonally asymmetrical trends in observations, so an alternative scenario of extrapolated trends was also explored. We conclude that interannual variability in climate will continue to have the dominant impact on water resources management whichever trajectory is followed. This demonstrates the need for sophisticated downscaling methods which can evaluate changes in variability and sequencing of events to explore climate change impacts in this region. © 2014. Source


Rameshwaran P.,UK Center for Ecology and Hydrology | Naden P.S.,UK Center for Ecology and Hydrology | Lawless M.,JBA Consulting Engineers and Scientists
Earth Surface Processes and Landforms | Year: 2011

A key problem in computational fluid dynamics (CFD) modelling of gravel-bed rivers is the representation of multi-scale roughness, which spans the range from grain size, through bedforms, to channel topography. These different elements of roughness do not clearly map onto a model mesh and use of simple grain-scale roughness parameters may create numerical problems. This paper presents CFD simulations for three cases: a plane bed of fine gravel, a plane bed of fine gravel including large, widely-spaced pebble clusters, and a plane gravel bed with smaller, more frequent, protruding elements. The plane bed of fine gravel is modelled using the conventional wall function approach. The plane bed of fine gravel including large, widely-spaced pebble clusters is modelled using the wall function coupled with an explicit high-resolution topographic representation of the pebble clusters. In these cases, the three-dimensional Reynolds-averaged continuity and Navier-Stokes equations are solved using the standard k-ε turbulence model, and model performance is assessed by comparing predicted results with experimental data. For gravel-bed rivers in the field, it is generally impractical to map the bed topography in sufficient detail to enable the use of an explicit high-resolution topography. Accordingly, an alternative model based on double-averaging is developed. Here, the flow calculations are performed by solving the three-dimensional double-averaged continuity and Navier-Stokes equations with the spatially-averaged 〈k-ε〉 turbulence model. For the plane bed of fine gravel including large, widely-spaced pebble clusters, the model performance is assessed by comparing the spatially-averaged velocity with the experimental data. The case of a plane gravel bed with smaller, more frequent, protruding elements is represented by a series of idealized hypothetical cases. Here, the spatially-averaged velocity and eddy viscosity are used to investigate the applicability of the model, compared with using the explicit high-resolution topography. The results show the ability of the model to capture the spatially-averaged flow field and, thus, illustrate its potential for representing flow processes in natural gravel-bed rivers. Finally, practical data requirements for implementing such a model for a field example are given. © 2011 John Wiley & Sons, Ltd. Source

Discover hidden collaborations