An extreme value analysis of the flow of Burbage Brook

An extreme value analysis of the flow of Burbage Brook is carried out by modelling peaks over a high threshold. The aims are to illustrate recently developed statistical techniques and to report on interesting features of the flow of the brook over a 58-year period. Peak flows are found to show marked seasonal variation and a downward trend. Then-year return level is estimated for various values ofn, and the reliability of the estimates is assessed.     

Visual pollution in a national park

National Parks in Britain are not in areas of wilderness, but inhabited and farmed land. This makes management of the Parks difficult and insufficient moral and financial support from local authorities has led to their progressive deterioration. They are designed for the enjoyment of the public, but can they survive ‘people pollution’?     

Reply to Discussion of “Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example”*

ABSTRACT

Ertsen discusses the representation of reality and uncertainty in our paper, raising three critical points. In response to the first, we agree that discussion of different interpretations of the concept of uncertainty is important when developing perceptual models – making different uncertainty interpretations explicit was a key motivation behind our method. Secondly, we do not, as Ertsen suggests, deny anyone who is not a “certified” scientist to have relevant knowledge. The elicitation of diverse views by discussing perceptual models is a basis for open discussion and decision making. Thirdly, Ertsen suggests that it is not useful to treat socio-hydrological systems as if they exist. We argue that we act as “pragmatic realists” in most practical applications by treating socio-hydrological systems as an external reality that can be known. But the uncertainty that arises from our knowledge limitations needs to be recognized, as it may impact on practical decision making and associated costs.     

Large-sample hydrology: recent progress,guidelines for new datasets and grand challenges

ABSTRACT

Large-sample hydrology (LSH) relies on data from large sets (tens to thousands) of catchments to go beyond individual case studies and derive robust conclusions on hydrological processes and models. Numerous LSH datasets have recently been released, covering a wide range of regions and relying on increasingly diverse data sources to characterize catchment behaviour. These datasets offer novel opportunities, yet they are also limited by their lack of comparability, uncertainty estimates and characterization of human impacts. This article (i) underscores the key role of LSH datasets in hydrological studies, (ii) provides a review of currently available LSH datasets, (iii) highlights current limitations of LSH datasets and (iv) proposes guidelines and coordinated actions to overcome these limitations. These guidelines and actions aim to standardize and automatize the creation of LSH datasets worldwide, and to enhance the reproducibility and comparability of hydrological studies.     

Small oil spill kills 10–20 000 seabirds in North Norway

An estimated 10–20 000 seabirds were killed by a very small oil spill off the coast of North Norway in March 1979. Despite the fact that over 90% of these were Brunnich's Guillemots Uria lomvia, the breeding population of this species was not considered to have been seriously threatened by this spill. On the other hand, this episode did illustrate how extremely vulnerable certain seabird species are to oil.     

Ophiolitic breccias associated with allochthonous oceanic crustal rocks in the East Ligurian Apennines,Italy — a comparison with observations from rifted oceanic ridges

In the East Ligurian segment of the North Apennines, eugeosynclinal sequences which contain ophiolitic rocks have been tectonically emplaced onto approximately coeval miogeosynclinal sediments. These allochthonous sequences represent the floor of a Mesozoic ocean which closed during the early Tertiary. The ophiolitic rocks consist of serpentinite, gabbro, pillowed and massive basalts, and breccias derived from these lithologies. They are overlain with depositional contacts by Upper Jurassic-Cretaceous pelagic cherts, limestones, and a shale/limestone sequence.The ophiolitic breccias attain thicknesses up to 100 m and strike lengths up to a few kilometres, and consist largely of unorganized accumulations of sand- to block-sized clasts. Compositions at specific horizons may range from oligomict breccias containing gabbro, basalt, or serpentinite fragments, to polymict breccias consisting of any mixture of these lithologies. Most of the breccias probably represent slow talus accumulations at the base of major submarine fault scarps which have exposed gabbro and serpentinite to submarine erosion. Direct exposure of gabbro and serpentinite on the ocean floor is also indicated by the occurrence of stratigraphically intact contacts between these lithologies and overlying pelagic sediments (generally cherts). The distribution and thickness of the breccias and volcanics, and the distribution of the gabbro and serpentinite, can vary greatly within distances of a few kilometres, thus producing complex heterogeneous sequences consisting of laterally impersistent lithological units.Recent observations and deep drilling of the Mid-Atlantic Ridge and other rifted ridges have revealed occurrences of significant thicknesses of basaltic, serpentinitic, and gabbroic breccias upon and within the volcanic layer of the oceanic crust, as well as the direct submarine exposure of plutonic rocks. It is therefore likely that the East Ligurian sequences represent parts of rifted ridge-generated crust. If so, then the complexity of the East Ligurian sequences suggests that the upper part of rifted ridge-generated crust may in places possess large variations in its stratigraphy over small (<10 km²) areas.Smooth, non-rifted (fast-spreading) ridges, which have very reduced topography and lack major fault scarps, should form ophiolitic complexes deficient in breccias containing fragments of plutonic igneous rocks. Most large ophiolitic complexes do not contain plutonic rock-bearing breccias, and were therefore probably formed at smooth ridges. The apparently preferential preservation of this type of ophiolitic complex, as opposed to the rifted ridge-type crust in East Liguria, may be related to the less pervasive and less intense fracturing of smooth ridges. This resulted in greater “cohesion” and lateral continuity of smooth ridge-generated crust during later tectonic emplacement into allochthonous positions in orogenic belts.     

Hydrologic characteristics of lake‐ and stream‐side riparian wetted margins in the McMurdo Dry Valleys,Antarctica

Water is a limiting factor for life in the McMurdo Dry Valleys (MDV), Antarctica. The active layer (seasonally thawed soil overlying permafrost) accommodates dynamic hydrological and biological processes for 10–16 weeks per year. Wetted margins (visually wetted areas with high moisture content) adjacent to lakes and streams are potential locations of great importance in the MDV because of the regular presence of liquid water, compared with the rest of the landscape where liquid water is rare. At 11 plots (four adjacent to lakes, seven adjacent to streams), soil particle size distribution, soil electrical conductivity, soil water content and isotopic signature, width of the wetted margin, and active layer thaw depth were characterised to determine how these gradients influence physicochemical properties that determine microbial habitat and biogeochemical cycling. Sediments were generally coarse‐grained in wetted margins adjacent to both lakes and streams. Wetted margins ranged from 1·04 to 11·01 m in average length and were found to be longer at lakeside sites than streamside. Average thaw depths ranged from 0·12 to 0·85 m, and were found to be deepest under lake margins. Lake margins also had much higher soil electrical conductivity, steeper topographic gradients, but more gradual soil moisture gradients than stream margins. Patterns of soil water δ¹⁸O and δD distribution indicate capillary action and evaporation from wetted margins; margin pore waters generally demonstrated isotopic enrichment with distance from the shore, indicating evaporation of soil water. Lake margin pore waters were significantly more negative in D_XS (D_XS = δD‐8δ¹⁸O) than streamside pore waters, indicating a longer history of evaporation there. Differences between lake and stream margins can be explained by the more consistent availability of water to lake margins than stream margins. Differences in margin characteristics between lakes and streams have important consequences for the microbial habitat of these margins and their functional role in biogeochemical cycling at these terrestrial–aquatic interfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

The initial responses of hot liquid water released under low atmospheric pressures: Experimental insights

Experiments have been performed to simulate the shallow ascent and surface release of water and brines under low atmospheric pressure. Atmospheric pressure was treated as an independent variable and water temperature and vapor pressure were examined as a function of total pressure variation down to low pressures. The physical and thermal responses of water to reducing pressure were monitored with pressure transducers, temperature sensors and visible imaging. Data were obtained for pure water and for solutions with dissolved NaCl or CO₂. The experiments showed the pressure conditions under which the water remained liquid, underwent a rapid phase change to the gas state by boiling, and then solidified because of removal of latent heat. Liquid water is removed from phase equilibrium by decompression. Solid, liquid and gaseous water are present simultaneously, and not at the 611 Pa triple point, because dynamic interactions between the phases maintain unstable temperature gradients. After phase changes stop, the system reverts to equilibrium with its surroundings. Surface and shallow subsurface pressure conditions were simulated for Mars and the icy satellites of the outer Solar System. Freezing by evaporation in the absence of wind on Mars is shown to be unlikely for pure water at pressures greater than c. 670 Pa, and for saline solutions at pressures greater than c. 610 Pa. The physical nature of ice that forms depends on the salt content. Ice formed from saline water at pressures less than c. 610 Pa could be similar to terrestrial sea ice. Ice formed from pure water at pressures less than c. 100 Pa develops a low thermal conductivity and a ‘honeycomb’ structure created by sublimation. This ice could have a density as low as c. 450 kg m⁻³ and a thermal conductivity as low as 1.6 W m⁻¹ K⁻¹, and is highly reflective, more akin to snow than the clear ice from which it grew. The physical properties of ice formed from either pure or saline water at low pressures will act to reduce the surface temperature, and hence rate of sublimation, thereby prolonging the lifespan of any liquid water beneath.     

Radiative acceleration in Schwarzschild space–times

We examine the radial motion of a material particle in the intense radiation field of a static spherically symmetric compact object with spherical emitting surface outside the Schwarzschild radius. This paper generalizes previous work which dealt with radial motion in the Thomson limit, where the radiation force is simply proportional to the radiative flux. In the general case the average time component of the 4-momentum transferred to the particle is not negligible compared with its rest mass. Consequently, we find that the frequency dependence of the radiation force owing to Compton scattering for highly energetic photons gives rise to an increase in the effective mass of the test particle. In this work we outline the effects of this frequency dependence and compare these with the results in the Thomson limit. We present the frequency dependent saturation velocity curves for a range of stellar luminosities and radiation frequencies and present the resulting phase-space diagrams corresponding to the radial test particle trajectories. In particular, the stable equilibrium points which exist in the Thomson limit are found to be absent in the general case.     

Thirteen plus one: a comparison of global climate policy architectures

We critically review the Kyoto Protocol and thirteen alternative policy architectures for addressing the threat of global climate change. We employ six criteria to evaluate the policy proposals: environmental outcome, dynamic efficiency, cost-effectiveness, equity, flexibility in the presence of new information, and incentives for participation and compliance. The Kyoto Protocol does not fare well on a number of criteria, but none of the alternative proposals fare well along all six dimensions. We identify several major themes among the alternative proposals: Kyoto is “too little, too fast”; developing countries (DCs) should play a more substantial role and receive incentives to participate; implementation should focus on market-based approaches, especially those with price mechanisms; and participation and compliance incentives are inadequately addressed by most proposals. Our investigation reveals tensions among several of the evaluative criteria, such as between environmental outcome and efficiency, and between cost-effectiveness and incentives for participation and compliance.