Scaling of the Vertical Spreading of a Plume of a Passive Tracer in a Rough-Wall Neutral Boundary Layer

The influence of surface roughness on the dispersion of a passive scalar in a rough wall turbulent boundary layer has been studied using wind-tunnel experiments. The surface roughness was varied using different sizes of roughness elements, and different spacings between the elements. Vertical profiles of average concentration were measured at different distances downwind of the source, and the vertical spread of the plume was computed by fitting a double Gaussian profile to the data. An estimate of the integral length scale is derived from the turbulence characteristics of the boundary layer and is then used to scale the measured values of plume spread. This scaling reduces the variability in the data, confirming the validity of the model for the Lagrangian integral time scale, but does not remove it entirely. The scaled plume spreading shows significant differences from predictions of theoretical models both in the near and in the far field. In the region immediately downwind of the source this is due to the influence of the wake of the injector for which we have developed a simple model. In the far field we explain that the differences are mainly due to the absence of large-scale motions. Finally, further downwind of the source the scaled values of plume spread fall into two distinct groups. It is suggested that the difference between the two groups may be related to the lack of dynamical similarity between the boundary-layer flows for varying surface roughness or to biased estimates of the plume spread.     

Evaluation of a high-resolution regional climate simulation over Greenland

A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model (RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than 60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations.     

On the Retrieval of Volcanic Sulfur Dioxide Emissions from GOME Backscatter Measurements

We focus on the retrieval of volcanic sulfur dioxide (SO₂) emissions from an analysis of atmospheric UV backscatter spectra obtained by the Global Ozone Monitoring Experiment (GOME) spectrometer on board the ESA European Remote Sensing Satellite (ERS-2). Here, the last major eruptions of Mt. Etna on Sicily (Italy) in July/August 2001 and October/November 2002 provided an excellent opportunity to study the retrieval of SO₂ columnar amounts from ground-based, LIDAR and satellite measurements. Our study shows that the bulk of emitted SO₂ was confined in the troposphere, mainly between 700 hPa and 400 hPa which is confirmed by trajectory analysis, by LIDAR observations and AVHRR observations. The area of influence of Mt. Etna eruptions ranges from the Western Saharan Desert to Greece and the near east states and even down to the basin of Tschad, Africa. Our analysis revealed that information about the plume height of volcanic eruptions and aerosol parameters is necessary for a reliable quantitative retrieval of SO₂ from space-borne sensor data at periods perturbed by volcanic eruptions.     

Assessing market and non-market costs of freshwater flooding due to climate change in the community of Fredericton, Eastern Canada

There is a general consensus that climate change will increase the frequency and severity of freshwater flooding in many parts of the world. Communities prone to such flooding have struggled to understand the manner in which this will affect them (in both economic and social terms) and the appropriate way to adapt. In this study, we conduct a case-study investigation into the costs of freshwater flooding due to climate change along the Saint John River in Fredericton, NB, Canada. We develop a four-step framework that combines extreme event analysis, downscaled general circulation models, hydrologic analysis, and the contingent valuation method. Using this framework, together with primary data on a 2005 flooding event, we estimate market and non-market annual average flood damage under a number of climate and population scenarios. We find that non-market costs can represent up to 50% of total household costs of flooding events, and 23–42% of the total costs of flooding due to climate change, depending on the different climate and population scenarios considered. Incorporating such costs into flood adaptation planning may substantially increase support for active adaptation activities, especially in ‘worst case’ climate scenarios.     

Top-down and bottom-up modelling to support low-carbon scenarios: climate policy implications

Bottom-up and top-down models are used to support climate policies, to identify the options required to meet GHG abatement targets and to evaluate their economic impact. Some studies have shown that the GHG mitigation options provided by economic top-down and technological bottom-up models tend to vary. One reason for this is that these models tend to use different baseline scenarios. The bottom-up TIMES_PT and the top-down computable general equilibrium GEM-E3_PT models are examined using a common baseline scenario to calibrate them, and the extend of their different mitigation options and its relevant to domestic policy making are assessed. Three low-carbon scenarios for Portugal until 2050 are generated, each with different GHG reduction targets. Both models suggest close mitigation options and locate the largest mitigation potential to energy supply. However, the models suggest different mitigation options for the end-use sectors: GEM-E3_PT focuses more on energy efficiency, while TIMES_PT relies on decrease carbon intensity due to a shift to electricity. Although a common baseline scenario cannot be ignored, the models’ inherent characteristics are the main factor for the different outcomes, thereby highlighting different mitigation options.

Policy relevance

The relevance of modelling tools used to support the design of domestic climate policies is assessed by evaluating the mitigation options suggested by a bottom-up and a top-down model. The different outcomes of each model are significant for climate policy design since each suggest different mitigation options like end-use energy efficiency and the promotion of low-carbon technologies. Policy makers should carefully select the modelling tool used to support their policies. The specific modelling structures of each model make them more appropriate to address certain policy questions than others. Using both modelling approaches for policy support can therefore bring added value and result in more robust climate policy design. Although the results are specific for Portugal, the insights provided by the analysis of both models can be extended to, and used in the climate policy decisions of, other countries.     

Perceptions and responses to climate policy risks among California farmers

This paper considers how farmers perceive and respond to climate change policy risks, and suggests that understanding these risk responses is as important as understanding responses to biophysical climate change impacts. Based on a survey of 162 farmers in California, we test three hypotheses regarding climate policy risk: (1) that perceived climate change risks will have a direct impact on farmer's responses to climate policy risks, (2) that previous climate change experiences will influence farmer's climate change perceptions and climate policy risk responses, and (3) that past experiences with environmental policies will more strongly affect a farmer's climate change beliefs, risks, and climate policy risk responses. Using a structural equation model we find support for all three hypotheses and furthermore show that farmers’ negative past policy experiences do not make them less likely to respond to climate policy risks through participation in a government incentive program. We discuss how future research and climate policies can be structured to garner greater agricultural participation. This work highlights that understanding climate policy risk responses and other social, economic and policy perspectives is a vital component of understanding climate change beliefs, risks and behaviors and should be more thoroughly considered in future work.     

The Inclusion of Stakeholder Knowledge and Perspectives in Integrated Assessment of Climate Change

Over the past few decades Integrated Assessment (IA) has emerged as an approach to link knowledge and action in a way that is suitable to accommodate uncertainties, complexities and value diversities of global environmental risks. Responding to the complex nature of the climate problem and to the changing role of climate change in the international climate policy process, the scientific community has started to include stakeholder knowledge and perspectives in their assessments. Participatory Integrated Assessment (PIA) is in its early stage of development. Methodology varies strongly across PIA projects. This paper analyzes four recent IA projects of climate change that included knowledge or perspectives from stakeholders in one-way or another. Approaches and methods used turn out to differ in whether stakeholders are involved actively or passively, whether the approach is bottom-up or top-down, and whether the different functions in the IA process are open or closed to stakeholder input. Also, differences can be seen in the degree to which boundaries are pre-set that limit the roles and domains of competencies attributed to each scientific or non-scientific participant (so-called boundary work). The paper discusses pros and cons of the various approaches identified, and outlines heuristics and considerations to assist those who plan, design or fund new IA processes with stakeholder input on what approaches best to choose in view of the objectives for stakeholder involvement, in view of the role that the IA plays in the overall risk management process and in view of considerations regarding boundary work.     

Flexural subsidence by 29 Ma on the NE edge of Tibet from the magnetostratigraphy of Linxia Basin, China

This study provides a detailed magnetostratigraphic record of subsidence in the Linxia Basin, documenting a 27 Myr long sedimentary record from the northeastern edge of the Tibetan Plateau. Deposition in the Linxia Basin began at 29 Ma and continued nearly uninterruptedly until 1.7 Ma. Increasing rates of subsidence between 29 and 6 Ma in the Linxia Basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to Late Oligocene–Late Miocene time. By Late Miocene–Early Pliocene time, a decrease in subsidence rates in the Linxia Basin associated with thrust faulting and a 10° clockwise rotation in the basin indicates that the deformation front of the Tibetan plateau had propagated into the currently deforming region northeast of the plateau.     

An environmental assessment of the Charleston Ocean Dredged Material Disposal Site and surrounding areas after partial completion of the Charleston Harbor Deepening Project

A project to deepen shipping and entrance channels in Charleston Harbor was conducted from 1999 to 2002. This generated approximately 22 million cubic yards of sediment for offshore disposal. Assessments of biological and physical conditions in the Charleston Ocean Dredged Material Disposal Site and surrounding areas were conducted prior to deepening (1993-94), and partway through the disposal period (2000). Results from the 2000 survey are presented and compared to the baseline survey. The study area was composed of the disposal zone and surrounding areas and divided into 20 one square mile strata. Within each stratum, benthic grab samples were collected from ten random sites for analysis of sediment composition and contaminants and macrobenthic assemblages. No contaminant levels were above effects range low levels. Results revealed that sediments in the western strata had significantly higher silt/clay content in the 2000 survey when compared to baseline sediments, while sediments east of the disposal zone were similar to baseline. Analyses were performed on a subset of the benthic data that compared baseline to 2000 conditions in western and eastern strata. The benthic communities in western strata were altered following disposal operations. The benthic community east of the disposal area was not different from baseline conditions. These alterations in the benthic community were attributed to changes in bottom habitat characteristics rather than pollution effects.     

Deriving TDS values in coarse sediments from long normal and electromagnetic logs

This paper presents an empirical relationship of quantitatively linked electromagnetic (EM) borehole recordings of the total dissolved solids (TDS) in pore water in the Quaternary deposits of the Belgian coastal plain. First, the long normal (LN) logs are linked to EM logs, then the already developed relationships between LN resistivity measurements and the TDS values are rewritten for EM recordings. The main parameter in these equations is the formation factor, which is derived from ground water analyses and LN logs through Archie's law. The EM recording has several advantages compared to the LN logs. The EM analysis allows measuring in PVC-cased wells and is not hindered by the invasion zone around the well. Furthermore, it has a high vertical resolution. LN logs can be measured only once, after drilling a well; EM recordings can be repeated several times in monitoring wells, which allows the gathering of time-dependent data over a complete vertical cross section. Such data could be obtained with LN logs only in wells with screens over the full-depth interval, which causes a hydraulic short circuit. This short circuit can result in a large artificial flow through the well between different levels, resulting in a salinity profile, which is no longer representative for the studied site. Remediation against short circuiting is a reduction of the screened interval, which strongly reduces the gathered information. The application of the derived equations is one of setting up a monitoring network along the Belgian coast to monitor the trend in salinity levels and comparing present salinity levels with older LN recordings to investigate the salinity changes in the last 30 years. Deep wells already present in the Belgiancoastal plain can then be used to monitor both the fresh water head changes and the salt water evolution. The technique has also been used for parameter identification for which real concentration measurements were needed.