255 research outputs found
Modelling landscape controls on dissolved organic carbon sources and fluxes to streams
Acknowledgments We thank the Natural Environment Research Council NERC (project NE/K000268/1) for funding. Iain Malcolm and staff at Marine Scotland (Pitlochry) are also thanked for the provision of data from the AWS as are the Scottish Environmental Protection Agency and British Atmospheric Data Centre for the provision of meteorological data.Peer reviewedPublisher PD
Stream water age distributions controlled by storage dynamics and nonlinear hydrologic connectivity : Modeling with high-resolution isotope data
Peer reviewedPublisher PD
Modelling storage-driven connectivity between landscapes and riverscapes : towards a simple framework for long-term ecohydrological assessment
Acknowledgements: We thank Iain Malcolm of Marine Scotland Science for access to data from the Girnock and the Scottish Environment Protection Agency for historical stage-discharge relationships. CS contributions on this paper were in part supported by the NERC/JPI SIWA project (NE/M019896/1).Peer reviewedPublisher PD
Continuous Dissolved Oxygen Measurements and Modelling Metabolism in Peatland Streams
Stream water dissolved oxygen was monitored in a 3.2km2 moorland headwater catchment in the Scottish Highlands. The stream consists of three 1st order headwaters and a 2nd order main stem. The stream network is fringed by peat soils with no riparian trees, though dwarf shrubs provide shading in the lower catchment. Dissolved oxygen (DO) is regulated by the balance between atmospheric re-aeration and the metabolic processes of photosynthesis and respiration. DO was continuously measured for >1 year and the data used to calibrate a mass balance model, to estimate primary production, respiration and re-aeration for a 1st order site and in the 2nd order main stem. Results showed that the stream was always heterotrophic at both sites. Sites were most heterotrophic in the summer reflecting higher levels of stream metabolism. The 1st order stream appeared more heterotrophic which was consistent with the evident greater biomass of macrophytes in the 2nd order stream, with resulting higher primary productivity. Comparison between respiration, primary production, re-aeration and potential physical controls revealed only weak relationships. However, the most basic model parameters (e.g. the parameter linking light and photosynthesis) controlling ecosystem processes resulted in significant differences between the sites which seem related to the stream channel geometry
Linking high-frequency DOC dynamics to the age of connected water sources
Acknowledgments The authors would like to thank our NRI colleagues for all their help with field and laboratory work, especially Audrey Innes, Jonathan Dick, and Ann Porter. We would like to also thank Iain Malcolm (Marine Scotland Science) for providing AWS data and the European Research Council ERC (project GA 335910 VEWA) for funding the VeWa project. Please contact the authors for access to the data used in this paper. We would also like to thank the Natural Environment Research Council NERC (project NE/K000268/1) for funding.Peer reviewedPublisher PD
Process-informed subsampling improves subseasonal rainfall forecasts in Central America
Subseasonal rainfall forecast skill is critical to support preparedness for hydrometeorological extremes. We assess how a process-informed evaluation, which subsamples forecasting model members based on their ability to represent potential predictors of rainfall, can improve monthly rainfall forecasts within Central America in the following month, using Costa Rica and Guatemala as test cases. We generate a constrained ensemble mean by subsampling 130 members from five dynamic forecasting models in the C3S multimodel ensemble based on their representation of both (a) zonal wind direction and (b) Pacific and Atlantic sea surface temperatures (SSTs), at the time of initialization. Our results show in multiple months and locations increased mean squared error skill by 0.4 and improved detection rates of rainfall extremes. This method is transferrable to other regions driven by slowly-changing processes. Process-informed subsampling is successful because it identifies members that fail to represent the entire rainfall distribution when wind/SST error increases
A simple topography-driven and calibration-free runoff generation module
Reading landscapes and developing calibration-free runoff
generation models that adequately reflect land surface heterogeneities
remains the focus of much hydrological research. In this study, we report a
novel and simple topography-driven runoff generation parameterization – the
HAND-based Storage Capacity curve (HSC), which uses a topographic index
(HAND, Height Above the Nearest Drainage) to identify hydrological similarity
and the extent of saturated areas in catchments. The HSC can be used as a
module in any conceptual rainfall–runoff model. Further, coupling the HSC
parameterization with the mass curve technique (MCT) to estimate root zone
storage capacity (SuMax), we developed a calibration-free runoff
generation module, HSC-MCT. The runoff generation modules of HBV and TOPMODEL
were used for comparison purposes. The performance of these two modules (HSC
and HSC-MCT) was first checked against the data-rich Bruntland Burn (BB)
catchment in Scotland, which has a long time series of field-mapped
saturation area extent. We found that HSC, HBV and TOPMODEL all perform well
to reproduce the hydrograph, but the HSC module performs better in
reproducing saturated area variation, in terms of correlation coefficient and
spatial pattern. The HSC and HSC-MCT modules were subsequently tested for 323
MOPEX catchments in the US, with diverse climate, soil, vegetation and
geological characteristics. In comparison with HBV and TOPMODEL, the HSC
performs better in both calibration and validation, particularly in the
catchments with gentle topography, less forest cover, and arid climate.
Despite having no calibrated parameters, the HSC-MCT module performed
comparably well with calibrated modules, highlighting the robustness of the
HSC parameterization to describe the spatial distribution of the root zone
storage capacity and the efficiency of the MCT method to estimate
SuMax. This novel and calibration-free runoff generation module
helps to improve the prediction in ungauged basins and has great potential to
be generalized at the global scale.</p
On The Injection Spectrum of Ultrahigh Energy Cosmic Rays in the Top-Down Scenario
We analyze the uncertainties involved in obtaining the injection spectra of
UHECR particles in the top-down scenario of their origin. We show that the
DGLAP evolution of fragmentation functions (FF) to (mass of the X
particle) from their initial values at low is subject to considerable
uncertainties. We therefore argue that, for x\lsim 0.1 (the region of
interest for most large values of interest, being the
scaled energy variable), the FF obtained from DGLAP evolution is no more
reliable than that provided, for example, by a simple Gaussian form (in the
variable ) obtained under the Modified Leading Log Approximation
(MLLA). Additionally, we find that for x\gsim0.1, the evolution in of
the singlet FF, which determines the injection spectrum, is ``minimal'' -- the
singlet FF changes by barely a factor of 2 after evolving it over 14
orders of magnitude in . We, therefore, argue that as long as the
measurement of the UHECR spectrum above \sim10^{20}\ev is going to remain
uncertain by a factor of 2 or larger, it is good enough for most practical
purposes to directly use any one of the available initial parametrisations of
the FFs in the region x\gsim0.1 based on low energy data even without
evolving them to the requisite value.Comment: Minor changes, added a reference, version to appear in Phys. Rev.
Crossover quintessence and cosmological history of fundamental "constants"
Crossover quintessence predicts that the time variation of fundamental
couplings is substantially faster at redshift than over the past
few billion years. This could reconcile the reported time variation of the fine
structure constant from quasar absorption lines with severe bounds from
archeo-nuclear physics and high precision tests of the equivalence principle.
We present a model that is consistent with all present data on time varying
couplings, tests of the equivalence principle and cosmology.Comment: numerical example adapted to WMAP,published version,9 pages,LaTe
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