A multicriteria approach for flood risk mapping exemplified at the Mulde river,Germany

In this paper we develop a GIS-based multicriteria flood risk assessment and mapping approach. This approach includes flood risks which are not measured in monetary terms; it shows the spatial distribution of multiple risks, and it is able to deal with uncertainties in criteria values and to show their influence on the overall flood risk assessment. Additionally, the approach can be used to show the spatial allocation of the flood effects if risk reduction measures are implemented. The approach is applied to a pilot study for the River Mulde in Saxony, Germany, heavily affected by the hazardous flood in 2002. Therefore, a GIS database of economic, social and environmental risk criteria was created. Two different multicriteria decision rules, a disjunctive and an additive weighting approach, are utilised for an overall flood risk assessment in the area. For implementation, a software tool (FloodCalc) was developed supporting both, the risk calculation of the single criteria as well as the multicriteria analysis.

The graininess of dark matter haloes

We use the recently completed one billion particle Via Lactea II Λ cold dark matter simulation to investigate local properties like density, mean velocity, velocity dispersion, anisotropy, orientation and shape of the velocity dispersion ellipsoid, as well as the structure in velocity space of dark matter haloes. We show that at the same radial distance from the halo centre, these properties can deviate by orders of magnitude from the canonical, spherically averaged values, a variation that can only be partly explained by triaxiality and the presence of subhaloes. The mass density appears smooth in the central relaxed regions but spans four orders of magnitude in the outskirts, both because of the presence of subhaloes as well as of underdense regions and holes in the matter distribution. In the inner regions, the local velocity dispersion ellipsoid is aligned with the shape ellipsoid of the halo. This is not true in the outer parts where the orientation becomes more isotropic. The clumpy structure in local velocity space of the outer halo cannot be well described by a smooth multivariate normal distribution. Via Lactea II also shows the presence of cold streams made visible by their high 6D phase space density. Generally, the structure of dark matter haloes shows a high degree of graininess in phase space that cannot be described by a smooth distribution function.     

The evolution of star clusters: the resolved-star approach

We present the first results of a new technique to detect, locate, and characterize young dissolving star clusters. Using Hubble Space Telescope/Advanced Camera for Surveys archival images of the nearby galaxy IC2574, we performed stellar PSF photometry and selected the most massive stars as our first test sample. We used a group-finding algorithm on the selected massive stars to find cluster candidates. We then plot the color-magnitude diagrams for each group, and use stellar evolutionary models to estimate their age. So far, we found 79 groups with ages of up to about 100 Myr, displaying various sizes and densities.     

Multimass spherical structure models for N-body simulations

We present a simple and efficient method to set up spherical structure models for N -body simulations with a multimass technique. This technique reduces by a substantial factor the computer run time needed in order to resolve a given scale as compared to single-mass models. It therefore allows to resolve smaller scales in N -body simulations for a given computer run time. Here, we present several models with an effective resolution of up to  1.68 × 10⁹  particles within their virial radius which are stable over cosmologically relevant time-scales. As an application, we confirm the theoretical prediction by Dehnen that in mergers of collisionless structures like dark matter haloes always the cusp of the steepest progenitor is preserved. We model each merger progenitor with an effective number of particles of approximately 10⁸ particles. We also find that in a core–core merger the central density approximately doubles whereas in the cusp–cusp case the central density only increases by approximately 50 per cent. This may suggest that the central regions of flat structures are better protected and get less energy input through the merger process.     

对气候变化背景下中欧易北河流域可用水的评估

The Elbe region is representative of humid to semi-humid landscapes in Central Europe,where water availability during the summer season is the limiting factor for plant growth and crop yields.especially in the loess areas with high crop productivity having annual precipitation lower than 500 mm.This paper summarizes the results of the first phase of the GLOWA(GLObal WAter)-Elbe project and tries to assess the reliability of water supply in the German part of the Elbe river basin for the next 50 years,a time scale relevant for the implementation of water and land use management plans.One focus of the study was developing scenarios which are consistent with climate and land use changes considering possible uncertainties.The concluding result of the study is that nature and communities in parts of Central Europe will have to deal with considerably lower water resources under scenario conditions.     

Condensation and mixing in supernova ejecta

Low-density graphite spherules from the Murchison carbonaceous chondrite contain TiC grains and possess excess ²⁸Si and ⁴⁴Ca (from decay of short-lived ⁴⁴Ti). These and other isotopic anomalies indicate that such grains formed by condensation from mixtures of ejecta from the interior of a core-collapse supernova with those from the exterior. Using homogenized chemical and isotopic model compositions of the eight main burning zones as end-members, Travaglio et al. (1999) attempted to find mixtures whose isotopic compositions match those observed in the graphite spherules, subject to the condition that the atomic C/O ratio = 1. They were partially successful, but this chemical condition does not guarantee condensation of TiC at a higher temperature than graphite, which is indicated by the spherule textures. In the present work, model compositions of relatively thin layers of ejecta within the main burning zones computed by Rauscher et al. (2002) for Type II supernovae of 15, 21 and 25 M_? are used to construct mixtures whose chemical compositions cause equilibrium condensation of TiC at a higher temperature than graphite in an attempt to match the textures and isotopic compositions of the spherules simultaneously. The variation of pressure with temperature and the change in elemental abundances with time due to radioactive decay were taken into account in the condensation calculations. Layers were found within the main Ni, O/Ne, He/C and He/N zones that, when mixed together, simultaneously match the carbon, nitrogen and oxygen isotopic compositions, ⁴⁴Ti/⁴⁸Ti ratios and inferred initial ²⁶Al/²⁷Al ratios of the low-density graphite spherules, even at subsolar ¹²C/¹³C ratios. Due to the relatively large proportion of material from the Ni zone and the relative amounts of the two layers of the Ni zone required to meet these conditions, predicted ²⁸Si excesses are larger than observed in the low-density graphite spherules, and large negative δ⁴⁶Ti/⁴⁸Ti, δ⁴⁷Ti/⁴⁸Ti, δ⁴⁹Ti/⁴⁸Ti and δ⁵⁰Ti/⁴⁸Ti are produced, in contrast to the observed normal δ⁴⁶Ti/⁴⁸Ti and δ⁴⁷Ti/⁴⁸Ti, large positive δ⁴⁹Ti/⁴⁸Ti and smaller positive δ⁵⁰Ti/⁴⁸Ti. Although better matches to the observed δ⁴⁶Ti/⁴⁸Ti, δ⁴⁷Ti/⁴⁸Ti and ²⁸Si excesses can be found using much smaller amounts of Ni zone material and some Si/S zone material, it is very difficult to match simultaneously the Ti and Si isotopic compositions in any mixtures of material from these deep layers with He/C and He/N zone material, regardless of the condensation sequence. The occurrence of Fe-rich, Si-poor metal grains inside the graphite spherules does not have a satisfactory explanation.     

Carbon storage of headwater riparian zones in an agricultural landscape

Background

In agricultural regions, streamside forests have been reduced in age and extent, or removed entirely to maximize arable cropland. Restoring and reforesting such riparian zones to mature forest, particularly along headwater streams (which constitute 90% of stream network length) would both increase carbon storage and improve water quality. Age and management-related cover/condition classes of headwater stream networks can be used to rapidly inventory carbon storage and sequestration potential if carbon storage capacity of conditions classes and their relative distribution on the landscape are known.

Results

Based on the distribution of riparian zone cover/condition classes in sampled headwater reaches, current and potential carbon storage was extrapolated to the remainder of the North Carolina Coastal Plain stream network. Carbon stored in headwater riparian reaches is only about 40% of its potential capacity, based on 242 MgC/ha stored in sampled mature riparian forest (forest > 50 y old). The carbon deficit along 57,700 km headwater Coastal Plain streams is equivalent to about 25TgC in 30-m-wide riparian buffer zones and 50 TgC in 60-m-wide buffer zones.

Conclusions

Estimating carbon storage in recognizable age-and cover-related condition classes provides a rapid way to better inventory current carbon storage, estimate storage capacity, and calculate the potential for additional storage. In light of the particular importance of buffer zones in headwater reaches in agricultural landscapes in ameliorating nutrient and sediment input to streams, encouraging the restoration of riparian zones to mature forest along headwater reaches worldwide has the potential to not only improve water quality, but also simultaneously reduce atmospheric CO₂.     

A two‐step process for the reflooding of the Mediterranean after the Messinian Salinity Crisis

The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re‐visited onshore data from Italy and Turkey that lead to a new concept of a two‐step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600–900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub‐basins led to diachronous events such as the so‐called ‘Lago Mare’.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two‐step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies.