Using micro-catchment experiments for multi-local scale modelling of nature-based solutions

The Q-natural flood management project has co-developed with the Environment Agency 18 monitored micro-catchments (~1 km²) in Cumbria, UK installing calibrated flumes aimed at quantifying the potential shift in observed flows resulting from a range of nature-based-solutions installed by local organizations. The small-scale reduces the influence of variability characterizing larger catchments that would otherwise mask any such shifts, which we attempt to relate to a shift in model parameters. This paper demonstrates an approach to applying donor-parameter-shifts obtained from modelling two of the paired micro-catchments to a much larger scale, in order to understand the potential for improved distributed modelling of nature-based solutions in the form of additional tree-planting. The models include a rainfall-runoff model, Dynamic Topmodel, and a 2D hydrodynamic model, JFlow, permitting analysis of changes in hillslope processes and channel hydrodynamics resulting from a range of distributed measures designed to emulate natural hydrological processes that evaporate, store or infiltrate flows. We report on attempts to detect shift in hydrological response using one of the paired-micro-catchment moorland versus forestry sites in Lorton using Dynamic Topmodel. A donor-parameter-shift approach is used in a hypothetical experiment to represent new woodland in a much larger catchment, although testing all combinations of spatial planting strategies, responses to multiple-extremes, failure-modes and changes to synchronization becomes intractable to support good decision making. We argue that the problem can be re-framed to use donor-parameter-shifts at multi-local-scale catchments above communities known to be at risk, commensurate with most of the evidence of NbS impacts being effective at the small scale (ca. 10 km²). This might lead to more effective modelling to help catchment managers prioritize those communities-at-risk where there is more evidence that NbS might be effective.     

On accretion flow penetration of magnetospheres

We address the problem of plasma penetration of astrophysical magnetospheres, an important issue in a wide variety of contexts, ranging from accretion in cataclysmic variables to flows in protostellar systems. We point out that under well-defined conditions, penetration can occur without any turbulent mixing (driven, for example, by Rayleigh–Taylor or Kelvin–Helmholtz instabilities) caused by charge polarization effects, if the inflowing plasma is bounded in the direction transverse to both the flow velocity and the magnetic field. Depolarization effects limit the penetration depth, which nevertheless can, under specific circumstances, be comparable to the size of the magnetosphere. We discuss the effect of ambient medium on plasma propagation across the stellar magnetic field and determine the criteria for deep magnetosphere penetration. We show that, under conditions appropriate to magnetized white dwarfs in AM Her type cataclysmic variables, charge polarization effects can lead to deep penetration of the magnetosphere.     

A physical model of the high-frequency seismic signal generated by debris flows

We propose a physical model for the high-frequency (>1 Hz) spectral distribution of seismic power generated by debris flows. The modeled debris flow is assumed to have four regions where the impact rate and impulses are controlled by different mechanisms: the flow body, a coarser-grained snout, a snout lip where particles fall from the snout on the bed, and a dilute front composed of saltating particles. We calculate the seismic power produced by this impact model in two end-member scenarios, a thin-flow and thick-flow limit, which assume that the ratio of grain sizes to flow thicknesses are either near unity or much less than unity. The thin-flow limit is more appropriate for boulder-rich flows that are most likely to generate large seismic signals. As a flow passes a seismic station, the rise phase of the seismic amplitude is generated primarily by the snout while the decay phase is generated first by the snout and then the main flow body. The lip and saltating front generate a negligible seismic signal. When ground properties are known, seismic power depends most strongly on both particle diameter and average flow speed cubed, and also depends on length and width of the flow. The effective particle diameter for producing seismic power is substantially higher than the median grain size and close to the 73rd percentile for a realistic grain size distribution. We discuss how the model can be used to estimate effective particle diameter and average flow speed from an integrated measure of seismic power. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Object-oriented classification of very high resolution airborne imagery for the extraction of hedgerows and field margin cover in agricultural areas

The recent advancement in technology for the airborne collection and subsequent processing and analysis of digital remotely sensed data has been significant. An investigation into the contributions that recent developments have made to the assessment and extraction of hedgerow and field margins is presented. Research into the active legislation by which hedgerows and agricultural biodiversity in England are bound is brought together in the concept of an ideal classification. Using Leica Geosystems ADS40 data, collected for Berkshire (UK), the degree to which the ideal classification can be reached is investigated, focusing on the extraction of hedgerows and unploughed field margin protective boundary strips as image objects. Elevation data were derived from the ADS40 imagery data to accompany true-colour and colour-infrared spectral information. By buffering the detected hedgerow objects in a GIS, we facilitated an investigation of the presence of measures that satisfy the minimum hedgerow protection requirements stipulated by the UK Department for Environment, Food and Rural Affairs (DEFRA). In our study area, it was estimated that 68% of areas that need to be classified as ‘grassy hedgerow boundary strip’ to satisfy the minimum requirements of the legislation were established with low-lying grassy cover before the introduction of the legislation in July 2005. The implications of this research for the development of automated classification methods for field scale agricultural mapping are discussed.     

Atmospheric dispersion in the arctic: Winter-time boundary-layer measurements

The winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF₆ tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to 30 °C · (100 m)^-1) temperature inversions with light winds and a persistent weak (1 to 2 °C · (100 m)^-1) surface inversion with wind speeds up to 17 m s^-1. The absence of any diurnal atmospheric stability pattern during the study was due to the very limited solar insolation. Vertical profiles were measured with a multi-level mast from 1 to 17 m and with a Doppler acoustic sounder from 60 to 450 m. With high wind speeds, stable layers below 17 m and above 300 m were typically separated by a layer of neutral stability. Turbulence statistics and spectra calculated at a height of 33 m are similar to measurements reported for non-arctic, open terrain sites and indicate that the production of turbulence is primarily due to wind shear. The distribution of wind direction recorded at 1 Hz was frequently non-Gaussian for 1-hr periods but was always Gaussian for 5-min periods. We also observed non-Gaussian hourly averaged crosswind concentration profiles and assume that they can be modeled by calculating sequential short-term concentrations, using the 5-min standard deviation of horizontal wind direction fluctuations () to estimate a horizontal dispersion coefficient ( _y ), and constructing hourly concentrations by averaging the short-term results. Non-Gaussian hourly crosswind distributions are not unique to the arctic and can be observed at most field sites. A weak correlation between horizontal ( _v ) and vertical ( _w ) turbulence observed for both 1-hr and 5-min periods indicates that a single stability classification method is not sufficient to determine both vertical and horizontal dispersion at this site. An estimate of the vertical dispersion coefficient, _z , could be based on or a stability classification parameter which includes vertical thermal and wind shear effects (e.g., Monin-Obukhov length, L).     

Klimatische Tendenzen und Untersuchungen zur allgemeinen Zirkulation

Zusammenfassung Einige Beobachtungsdaten aus dem Winter 1962/63 werden sowohl in bezug auf neuere als auch auf langfristige klimatische Tendenzen diskutiert. Der Abkühlung der Weltklimate seit etwa 1940 ist bisher praktisch noch nicht viel Beachtung geschenkt worden, obwohl sie die Häufigkeit strengen Winterwetters beeinflußt hat. Dies ist vielleicht teilweise durch die künstliche Erwärmung der Städte zu erklären, die unter starken niedrig liegenden Temperaturinversionen im Winter am wirksamsten ist. Ferner wird über Untersuchungen der Änderungen der allgemeinen atmosphärischen Zirkulation berichtet. Diese zeigen den Mechanismus auf, durch den aufeinanderfolgende langfristige Klimaänderungen zustandegekommen sind: Die Abkühlung in den Jahren von 1300 bis 1600 und die Erwärmung in den Jahren von 1700 bis etwa 1930 werden mit einer Abschwächung beziehungsweise Verstärkung der Zirkulation bzw. mit entsprechenden Änderungen der Wellenlänge der zirkumpolaren Westdrift und einer Durchdringung der höchsten Breiten durch Warmluftzufuhr und Zyklonenzugbahnen in Verbindung gebracht. Eine Umkehr des Trends kann unter Verwendung dieser Zirkulations-Aspekte bereits früher entdeckt werden — schon 30 oder mehr Jahre früher — als durch Untersuchung der Temperaturen in der Arktis und anderswo, der Ausdehnung der Eisbedeckung usw. Es ist wahrscheinlich, daß die Abkühlung und die Zunahme des Eises, die jetzt speziell im europäischen Sektor zu beobachten sind, eine Reaktion darstellen auf die neuere Tendenz zu schwächerer zonaler Zirkulation hin und zu einer Westwärts-Verschiebung des Höhentroges im europäischen Sektor, die eine zunehmende Häufigkeit nördlicher Bodenwinde im Sektor zwischen Grönland und dem Ural begünstigt. Die Eislage in den nördlichen Meeren im Februar 1963 läßt sich nur mit den schlimmsten Jahren des 17. und 18. Jahrhunderts vergleichen.

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Summary Some figures for winter 1962/63 are examined in relation to both recent and long-term climatic trends. The cooling of world climates since about 1940 has not yet received much notice from the practical point of view, though it has affected the frequency of difficult winter weather. The oversight is perhaps partly explained by the increasing artificial warmth of the cities, which is most effective under strong low-level temperature inversions in winter. Studies of changes in the general atmospheric circulation are described. These show the mechanism by which successive long-term changes of climate have been achieved—cooling from 1300 to 1600 and warming from 1700 to about 1930—was associated respectively with weakening and strengthening circulation and corresponding changes of (a) wavelength in the circumpolar westerlies (b) penetration of the highest latitudes by advected warm air and depression tracks. Reversal of trend is detected earlier, already 30 years or more ago, in these aspects of the circulation than when one examines temperatures in the Arctic and elsewhere, extent of ice etc. It seems probable that the cooling and increase of ice now to be observed particularly in the European sector are a response to the recent trend towards weaker zonal circulation and a westward shift of the upper trough in the European sector which favours increased frequency of northerly surface winds in the sector between Greenland and the Urals. The ice situation on the northern seas in February 1963 appears fully comparable only with the worst years of the 17th and 18th centuries.

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Résumé On discute ici quelques observations de l'hiver 1962–1963 à la lumière de tendances climatologiques tant récentes qu'à long terme. Jusqu'ici, on n'a pas accordé beaucoup d'attention au refroidissement des climats de notre globe depuis 1930, bien que ce refroidissement ait influencé déjà le nombre des hivers rigoureux. Ce peu d'attention s'explique peutêtre par le chauffage artificiel des villes, chauffage qui est particulièrement efficace au-dessous de fortes inversions thermiques situées en hiver à basse altitude. On rapporte en outre sur des recherches concernant des changements de la circulation atmosphérique générale. Ces changements montrent le mécanisme par lequel les modifications successives du climat à long terme se sont produites. On met le refroidissement des années 1300 à 1600 en relation avec un ralentissement de la circulation et le réchauffement de 1700 à 1930 avec une accélération de cette circulation. On peut faire le même raprochement pour des modifications similaires de la longueur d'ondes du courant circumpolaire d'ouest et la pénétration des afflux d'air chaud et des trajectoires des cyclones aux latitudes les plus grandes. Une inversion de la tendance du climat peut être reconnue bien à l'avance—30 ans et plus—en utilisant ces nouveaux aspects de la circulation, qu'en utilisant les températures de l'arctique et d'ailleurs, l'extension de la calotte glaciaire, ou d'autres critères. Il est probable que le refroidissement et l'augmentation de la glace, visibles actuellement surtout dans le secteur européen, ne sont qu'une réaction aux nouvelles tendances de ralentissement de la circulation zonale et d'un déplacement vers l'ouest du creux dépressionnaire en altitude du secteur européen, ce qui favorise une fréquence accrue des vents du nord au sol entre le Groenland et l'Oural. La position des glaces dans les mers du nord en février 1963 ne peut être comparée qu'aux pires années des 17ème et 18ème siècles.

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Fluid inclusions in Adirondack granulites: Implications for the retrograde P-T path

Investigation of fluid inclusions in granitic and cale-silicate gneisses from the Adirondack Mountains, New York, has revealed the presence of various types, including: (1) CO₂-rich, (2) mixed H₂O–CO₂±salt and (3) aqueous inclusions with no visible CO₂. Many, if not all, of these inclusions were trapped or modified after the peak of granulite facies metamorphism, as shown by textural relations or by the lack of agreement between the composition of the fluids found in some inclusions and the composition of the peak-metamorphic fluid as estimated from mineral equilibria. Many fluid inclusions record conditions attained during retrograde cooling and uplift, with minimum pressures and temperatures of 2 to 3 kbar and 200 to 300°C. The temperatures and pressures derived from the investigation of these inclusions constrain the retrograde P-T path, and the results indicate that a period of cooling with little or no decompression.     

A system-level modelling perspective of the KwaZulu-Natal Bight ecosystem,eastern South Africa

The KwaZulu-Natal Bight comprises the only sizeable shelf region on the eastern coast of South Africa, and is influenced by both the Agulhas Current on its seaward side and rivers and estuaries on its landward side. Established knowledge of the effect of the Agulhas Current includes the influence on nutrient concentrations in the bight of a semi-permanent upwelling cell at its northern border (St Lucia) and, to a much lesser extent, of a semi-permanent eddy feature at its southern extremity. Current modelling efforts, however, point to a very important role of land-derived nutrients, which supplement the productivity of food webs of the bight. This connectivity of the bight to its adjacent ecosystems has various implications. First, its productivity has traditionally been viewed via phytoplankton growth, whereas ecosystem modelling efforts point to a very high reliance on imported detritus (mainly land-derived) in order to sustain especially the rich benthic food web. The benthos in the bight dominates the food web, and is in marked contrast to the upwelling system of the west coast of South Africa (Atlantic Ocean) where water-column productivity dominates. Second, the importance of the connectivity of the Thukela Bank prawn-trawling ground to estuarine nursery areas, which has been modelled quantitatively, highlights the significance of this particular ecosystem connectivity for fisheries and also for the Thukela Bank food web. Heterogeneity across the bight is apparent for nutrient turnover rates (carbon, nitrogen, phosphorus), CNP content and stoichiometry, whereas nitrogen is a limiting nutrient across the entire bight. The food web near the Thukela River is richer in nutrient content and more active (higher turnover rates) compared to the northern and southern parts of the bight. This environmental heterogeneity was also apparent from the CNP content and stoichiometry of the various species and species groups in the bight. Requirements to take the hydrodynamic, biogeochemical and first ecosystem modelling efforts towards a meaningful predictive capability are discussed. The importance of adopting a system-level view of the bight and its connected systems for realistic exploration of global change scenarios is highlighted.     

Methane emission measurements in urban areas in Eastern Germany

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m²/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States.     

Have applications of continuous rainfall–runoff simulation realized the vision for process‐based flood frequency analysis?

Keith Beven was amongst the first to propose and demonstrate a combination of conceptual rainfall–runoff modelling and stochastically generated rainfall data in what is known as the ‘continuous simulation’ approach for flood frequency analysis. The motivations included the potential to establish better links with physical processes and to avoid restrictive assumptions inherent in existing methods applied in design flood studies. Subsequently, attempts have been made to establish continuous simulation as a routine method for flood frequency analysis, particularly in the UK. The approach has not been adopted universally, but numerous studies have benefitted from applications of continuous simulation methods. This paper asks whether industry has yet realized the vision of the pioneering research by Beven and others. It reviews the generic methodology and illustrates applications of the original vision for a more physically realistic approach to flood frequency analysis through a set of practical case studies, highlighting why continuous simulation was useful and appropriate in each case. The case studies illustrate how continuous simulation has helped to offer users of flood frequency analysis more confidence about model results by avoiding (or exposing) bad assumptions relating to catchment heterogeneity, inappropriateness of assumptions made in (UK) industry‐standard design event flood estimation methods, and the representation of engineered or natural dynamic controls on flood flows. By implementing the vision for physically realistic analysis of flood frequency through continuous simulation, each of these examples illustrates how more relevant and improved information was provided for flood risk decision‐making than would have been possible using standard methods. They further demonstrate that integrating engineered infrastructure into flood frequency analysis and assessment of environmental change are also significant motivations for adopting the continuous simulation approach in practice. Copyright © 2016 John Wiley & Sons, Ltd.