Key climate indices in Switzerland; expected changes in a future climate

Climate indices facilitate the interpretation of expected climate change impacts for many sectors in society, economy, and ecology. The new localized data set of climatic change signals for temperature and precipitation presented by Zubler et al. (Clim Change, 2013) is applied for an analysis of frequently used climate indices in Switzerland. The indices considered are: number of summer days and tropical nights, growing season length, number of frost days and ice days, heating and cooling degree days, and the number of days with fresh snow. For the future periods 2020-49, 2045-74 and 2070–2099 the indices are computed using a delta-change approach based on the reference period 1980–2009 for the emission scenarios A1B, A2, and RCP3PD. The scenario data suggest the following relevant findings: (1) a doubling of the number of summer days by the end of the century under the scenarios A1B and A2, (2) an appearance of tropical nights even above 1500 m asl, (3) a possible reduction of the number of frost days by more than 3 months at altitudes higher than 2500 m asl, (4) a decline of heating degree days by about 30 % until the end of the century, and (5) the near disappearance of days with fresh snow at low altitudes. It is also shown that the end-of-the-century projections of all indices strongly depend on the chosen emission scenario.     

Teleconnection–extreme precipitation relationships over the Mediterranean region

The relationship between five teleconnection patterns (North Atlantic Oscillation (NAO), Arctic Oscillation (AO), East Atlantic/Western Russian (EAWR) pattern, Scandinavian (SCAND) pattern, and El Niño Southern Oscillation (ENSO)) and the frequency of occurrence of days (per month) with extreme precipitation in the Euro-Mediterranean region is investigated with National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data. To quantify the teleconnection–precipitation relationships over the Euro-Mediterranean region, linear correlations are calculated between the monthly teleconnection indices for the five patterns and time series at each grid point of the monthly frequency of days with extreme precipitation, focusing on daily precipitation amounts that exceed a particular threshold value (a 90 % threshold is used). To evaluate dynamical processes, the teleconnection indices are also correlated with the frequencies of days with extreme values of dynamic tropopause pressure and precipitable water. The former quantity is used as a proxy for potential vorticity intrusions and the latter to identify regions of enhanced moisture. The results of this analysis indicates positive, statistically significant correlations between the NAO, AO, and SCAND indices and the frequency of extreme precipitation in the western Mediterranean; positive (negative) correlations between the EAWR index and the extreme precipitation frequency in the eastern (western) Mediterranean; and a positive correlation between the Niño3.4 index and the extreme precipitation frequency over the Iberian Peninsula and the Middle East. For all of the teleconnection patterns other than ENSO, the dynamic tropopause pressure correlation patterns resemble those for the precipitation. In contrast, similar precipitation and precipitable water correlation patterns are observed only for ENSO. These findings suggest that the teleconnections affect the interannual variation of the frequency of days with extreme precipitation over a large part of the Euro-Mediterranean region through their impact on the spatial distribution of regions with enhanced potential vorticity and air moisture.     

Salt-marsh foraminifera in Ho Bugt,western Denmark,and their use as sea-level indicators

Twenty-seven surface samples were collected from the Kjelst Enge salt marsh in Ho Bugt, Jutland, to investigate the potential use of salt-marsh foraminifera as sea-level indicators in Holocene intertidal deposits. Previous work from many coastlines around the world has shown that the vertical distribution of salt-marsh foraminifera is strongly controlled by the duration of tidal flooding (or height relative to tide level). Concentrations of foraminifera in Kjelst Enge salt marsh are low, especially in the high marsh, but a strong correlation was found between relative abundances of foraminiferal species and tidal elevation for 16 samples containing more than 30 specimens per 5 cc of sediment (r² = 0.80, root mean square error = 0.16 m). Sediment pH also has a strong influence on the distribution of the foraminifera, but salinity appears to be insignificant.     

Comparing expert judgement and numerical criteria for hydrograph evaluation

Abstract

This paper investigates the relationship between expert judgement and numerical criteria when evaluating hydrological model performance by comparing simulated and observed hydrographs. Using a web-based survey, we collected the visual evaluations of 150 experts on a set of high- and low-flow hydrographs. We then compared these answers with results from 60 numerical criteria. Agreement between experts was found to be more frequent in absolute terms (when rating models) than in relative terms (when comparing models), and better for high flows than for low flows. When comparing the set of 150 expert judgements with numerical criteria, we found that most expert judgements were loosely correlated with a numerical criterion, and that the criterion that best reflects expert judgement varies from expert to expert. Overall, we identified two groups of 10 criteria yielding an equivalent match with the expertise of the 150 participants in low and high flows, respectively. A single criterion common to both groups (the Hydrograph Matching Algorithm with mean absolute error) may represent a good indicator for the overall evaluation of models based on hydrographs. We conclude that none of the numerical criteria examined here can fully replace expert judgement when rating hydrographs, and that both relative and absolute evaluations should be based on the judgement of multiple experts.

Editor D. Koutsoyiannis     

Interpretation of a Pumping Test with Interference from a Neighboring Well

In confined aquifers, the influence of neighboring active wells is often neglected when interpreting a pumping test. This can, however, lead to an erroneous interpretation of the pumping test data. This paper presents simple methods to evaluate the transmissivity (T) and storativity (S) of a confined aquifer under Theis conditions, when an interfering well starts pumping in the neighborhood of the tested well before the beginning of the test. These new methods yield better estimates of the T and especially S values than when the interfering well influence is neglected. They also permit to distinguish between interfering wells and other deviations from the Cooper‐Jacob straight line, such as impermeable boundaries. The new methods were then applied on data obtained from a numerical model. The new methods require knowing the pumping rate of the interfering well and the time elapsed since the pumping started in each well, but contrary to previous methods, they do not require the aquifer natural level at the beginning of the test, which is often unknown if the interfering well has started pumping before the tested well.     

A noniterative design procedure for supplemental brace–damper systems in single‐degree‐of‐freedom systems

In this paper, a method for designing supplemental brace–damper systems in single‐degree‐of‐freedom (SDOF) structures is presented. We include the effects of the supporting brace stiffness in the dynamic response by using a viscoelastic Maxwell model. On the basis of the study of an SDOF under ground excitation, we propose a noniterative design procedure for simultaneously specifying both the damper and the brace while assuring a desired structural performance. It is shown that to increase the damper size beyond the value delivered by the proposed criteria will not provide any improvement but actually worsen the structural response. The design method presented here shows excellent agreement with the FEMA 273 design approach but offers solutions closer to optimality. Copyright © 2013 John Wiley & Sons, Ltd.     

Energetic electron observations of Rhea’s magnetospheric interaction

Saturn’s moon Rhea is thought to be a simple plasma absorber, however, energetic particle observations in its vicinity show a variety of unexpected and complex interaction features that do not conform with our current understanding about plasma absorbing interactions. Energetic electron data are especially interesting, as they contain a series of broad and narrow flux depletions on either side of the moon’s wake. The association of these dropouts with absorption by dust and boulders orbiting within Rhea’s Hill sphere was suggested but subsequently not confirmed, so in this study we review data from all four Cassini flybys of Rhea to date seeking evidence for alternative processes operating within the moon’s interaction region. We focus on energetic electron observations, which we put in context with magnetometer, cold plasma density and energetic ion data. All flybys have unique features, but here we only focus on several structures that are consistently observed. The most interesting common feature is that of narrow dropouts in energetic electron fluxes, visible near the wake flanks. These are typically seen together with narrow flux enhancements inside the wake. A phase-space-density analysis for these structures from the first Rhea flyby (R1) shows that Liouville’s theorem holds, suggesting that they may be forming due to rapid transport of energetic electrons from the magnetosphere to the wake, through narrow channels. A series of possibilities are considered to explain this transport process. We examined whether complex energetic electron drifts in the interaction region of a plasma absorbing moon (modeled through a hybrid simulation code) may allow such a transport. With the exception of several features (e.g. broadening of the central wake with increasing electron energy), most of the commonly observed interaction signatures in energetic electrons (including the narrow structures) were not reproduced. Additional dynamical processes, not simulated by the hybrid code, should be considered in order to explain the data. For the small scale features, the possibility that a flute (interchange) instability acts on the electrons is discussed. This instability is probably driven by strong gradients in the plasma pressure and the magnetic field magnitude: magnetometer observations show clearly signatures consistent with the (expected) plasma pressure loss due to ion absorption at Rhea. Another potential driver of the instability could have been gradients in the cold plasma density, which are, however, surprisingly absent from most crossings of Rhea’s plasma wake. The lack of a density depletion in Rhea’s wake suggests the presence of a local cold plasma source region. Hybrid plasma simulations show that this source cannot be the ionized component of Rhea’s weak exosphere. It is probably related to accelerated photoelectrons from the moon’s negatively charged surface, indicating that surface charging may play a very important role in shaping Rhea’s magnetospheric interaction region.     

Interpreting nested storm event suspended sediment-discharge hysteresis relationships at large catchment scales

Reducing soil erosion and sediment delivery into rivers is a major aim for land management in New Zealand. Therefore, it is important to identify areas of sediment generation and their relationship to in-stream suspended sediment concentrations and water quality attributes. It is possible to infer and assess sediment sources and dynamics using storm event suspended sediment concentration-discharge hysteresis shape and loop direction. Research in small catchments has achieved some success; however, research in larger (>10³ km²) catchments has shown the inherent difficulty of interpreting hysteresis patterns at larger scales. In this paper, we use a nested, long-term suspended sediment monitoring program across a large catchment (3,903 km²: Manawatū in New Zealand) to address these challenges. We evaluate the hysteresis patterns of five major tributaries (subcatchment areas 329–1,298 km²) of the Manawatū River together with the hysteresis patterns at the gauged catchment outlet. Hysteresis patterns of the Manawatū subcatchments can be characterized as predominantly clockwise, that is, high hysteresis index (HI) value. Larger storms (discharge >2 × 10⁷ m³) increase the likelihood of clockwise hysteresis directions, whereas smaller storms (discharge <2 × 10⁷ m³) are more likely to be anticlockwise. The link between suspended sediment concentration-discharge hysteresis and subcatchment sediment sources becomes increasingly attenuated within the larger subcatchments. High antecedent discharge negatively correlates to HI values, suggesting conditions immediately before the storm have an influence on whether the catchment is “primed” or “exhausted” with available sediment. The different storm categories indicate that within this catchment, whereas hysteresis patterns vary due to the spatial origin of discharge and sediment to some extent, storm magnitude has a stronger impact on hysteresis dynamics than spatial origin.     

Seemingly disparate temperatures recorded in coexisting granulite facies lithologies

Phase equilibrium modelling of a conformable sequence of supracristal lithologies from the Bushmanland Subprovince of the Namaqua–Natal Metamorphic Complex (South Africa) reveals a disparity of some 60–70°C in estimated peak metamorphic temperature. Aluminous metapelites were equilibrated at ~770–790°C, whereas two‐pyroxene granulite and garnet–orthopyroxene–biotite gneiss record distinctly higher conditions of ~830–850°C. Semi‐pelite and Mg–Al‐rich gneisses yield poorly constrained estimates that span the range derived from other lithologies. All samples record peak pressure of ~5–6 kbar, and followed a roughly isobaric heating path from andalusite‐bearing greenschist/lower amphibolite facies conditions through a tight clockwise loop at near‐peak conditions, followed by near‐isobaric cooling. The disparity in peak temperatures appears to be robust, as the low‐variance assemblages in all samples reflect well‐known melting reactions that only occur over narrow temperature intervals. The stable coexistence of both products and reactants of these melting reactions indicates that they did not go to completion before metamorphism waned. Calculated pressure–enthalpy diagrams show that the melting reactions are strongly endothermic and therefore buffer temperature while heat is consumed by melting. Because the respective reactions occur at distinct P–T conditions and have different reactant assemblages, individual lithologies are thermally buffered at different temperatures and to different degrees, depending on the occurrence and abundance of reactant minerals. Our calculations show that all lithologies received essentially the same suprasolidus heat budget of 19 ± 1 kJ/mol, which led to the manifestation of lower peak temperatures in the more fertile and strongly buffered aluminous metapelites compared with more refractory rock types. If little to no thermal communication is assumed, this implies that lithology exerts a first‐order control over the heating path and the peak temperature that can be attained for a specific heat budget. Our results caution that the metamorphic conditions derived from pelitic granulites should not be assumed or extrapolated to larger sections of an orogenic crust that consist of other, more refractory lithologies.