Improved water table dynamics in MODFLOW

The standard formulation of a block-centered finite-difference model, such as MODFLOW, uses the center of the cell as the location of a cell node. Simulations of a dynamic water table can be improved if the node of a cell containing the water table is located at the water table rather than at the center of the cell. The LPF package of MOD-FLOW-2000 was changed to position a cell's node at the water table in convertible cells with a water table. Improved accuracy in the upper regions of an unconfined aquifer is demonstrated for pumping from a partially penetrating well. The change introduces a nonlinearity into the solution of the flow equations that results in slightly slower convergence of the flow solution, 7% slower in the presented demonstration. Accuracy of simulations is improved where vertical flow is dominated by a moving water table, but not when a large water table gradient dominates over the water table movement.     

Estimating australian forest fire danger under conditions of doubled carbon dioxide concentrations

The most appropriate indices with which to quantify Australian bushfire danger are the McArthur fire danger meters. These meters use meteorological information to produce a fire danger index that is directly related to the chance of a fire starting - and to the severity of a fire once it has started. The Mark 5 forest-fire danger meter uses air temperature, relative humidity and wind speed, plus a drought factor that is calculated using daily rainfall and temperature information.Three years of daily data generated from the CSIRO four-level general circulation model, and thirty years of daily data generated from the CSIRO nine-level model were used to estimate the daily McArthur forest fire danger index for simulations corresponding to present conditions, and to those corresponding to doubled atmospheric CO₂. The performance of these models with respect to fire danger was tested by comparing the fire danger index for Sale (in the Eastern part of Victoria, South-eastern Australia) calculated from analysis of daily climatological data with the modelled annual cumulative forest fire danger index for the grid point that was representative of Sale. Data from both models for all Australian grid points were also examined. Both models predict an increase in fire danger over much of Australia for their doubled CO₂ scenarios.The results from the models confirm that annually averaged daily relative humidity is the single most important variable in the estimation of forest fire danger on an annual basis, yet the models tend to produce relative humidities that are slightly too low so that the fire danger is overestimated. A simple one-box model of evaporation indicates that the value of relative humidity to be expected under an altered climatic regime depends on the modelled relation between actual and potential evaporation, the present values of relative humidity and evaporation rate, as well as on the expected changes in wind speed.     

Assessing the effectiveness of non-structural flood management measures in the Thames Estuary under conditions of socio-economic and environmental change

Risk analysis and appraisal of the benefits of structural flood risk management measures such as embankments is well established. Here, a method to quantify, over extended timescales, the effectiveness of non-structural measures such as land use spatial planning, insurance and flood resilient construction is presented. The integrated approach couples socio-economic and climate change scenarios with long term land use modelling and flood risk analysis to generate maps and time series of expected annual damages. The analysis has been applied on a case study in the Thames Estuary in the UK. Stakeholders helped develop a number of scenarios that might lead to substantial changes in existing planning and insurance policies in the UK. The effectiveness of these changes was analysed and showed the substantial benefits in terms of reduction of future flood risks that are achievable with changes in planning policy, financial incentives and resilient property construction in the floodplain. Moreover, the reward can be increased through earlier action. Subsequently, the benefits of a range of policies are explored under the UK Foresight socio-economic scenarios. Different structural and non structural flood management interventions are tested and the results demonstrate that despite the potential for large increases in flood risk in the Thames Estuary, in all scenarios substantial flood risk reductions are possible. The effectiveness of non-structural measures is however sensitive to socio-economic changes and governance arrangements. The analysis described here will help to identify portfolios of non-structural and structural options that are robust to uncertainties.     

A proposal for a new scenario framework to support research and assessment in different climate research communities

In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities.     

Towards the detection and attribution of an anthropogenic effect on climate

It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered [R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO₂ forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined sulfate aerosol/CO₂ experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of control run used to estimate natural variability noise properties. The R (t) trends for the CO₂-only signal are not significant in any season. C (t) trends for signals from both the CO₂-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here. The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless, we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global mean) components of a combined CO₂/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the detailed spatial signature in response to combined CO₂ and sulfate aerosol forcing, but not in response to CO₂ forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO₂-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change. Received: 10 November 1994 / Accepted: 19 July 1995     

Land use change under conditions of high population pressure: the case of Java

A long history of increases in population pressure in Java has caused agricultural land use to expand and intensify. More recent land use changes caused the conversion of prime agricultural land into residential and industrial area. Results of a dynamic, regional-scale, land use change model are presented, defining the spatial distribution of these land use changes. The model is based on multi-scale modelling of the relations between land use and socio-economic and biophysical determinants. Historical validation showed that the model can adequately simulate the pattern of land use change. Future patterns of land use change between 1994 and 2010 are simulated assuming further urbanization. The results suggest that most intensive land use changes will occur in Java's lowland areas.     

Detection of iodine monoxide radicals in the marine boundary layer using laser induced fluorescence spectroscopy

A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere. An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of the IO A²Π_3/2 ← X²Π_3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N₂O/CF₃I/N₂ mixtures with O₃ actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer) campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF.     

Enhancing the relevance of Shared Socioeconomic Pathways for climate change impacts,adaptation and vulnerability research

This paper discusses the role and relevance of the shared socioeconomic pathways (SSPs) and the new scenarios that combine SSPs with representative concentration pathways (RCPs) for climate change impacts, adaptation, and vulnerability (IAV) research. It first provides an overview of uses of social–environmental scenarios in IAV studies and identifies the main shortcomings of earlier such scenarios. Second, the paper elaborates on two aspects of the SSPs and new scenarios that would improve their usefulness for IAV studies compared to earlier scenario sets: (i) enhancing their applicability while retaining coherence across spatial scales, and (ii) adding indicators of importance for projecting vulnerability. The paper therefore presents an agenda for future research, recommending that SSPs incorporate not only the standard variables of population and gross domestic product, but also indicators such as income distribution, spatial population, human health and governance.     

Reflections on the current state of global climate response

What is the significance of the 2007 United Nations Climate Change Conference in Bali? The formal outcomes, especially the ‘Bali Action Plan’, are described and commented on, along with the challenges for negotiating a post-2012 agreement in Copenhagen during 2008 and 2009. The article concludes that the outcome of the Bali meeting is insufficient when compared to the nature of the challenge posed by climate change. However, it can nevertheless be considered a success in terms of ‘Realpolitik’ in paving the way for the negotiations ahead, because some real changes have been discerned in the political landscape. The challenges for the road towards Copenhagen are manifold: the sheer volume and complexity of the issues and the far-reaching nature of decisions such as differentiation between non- Annex I countries pose significant challenges in themselves, while the dependency on the electoral process in the USA introduces a high element of risk into the whole process. The emergence of social justice as an issue turns climate policy into an endeavour to improve the world at large—thereby adding to the complexity. And, finally, the biggest challenge is the recognition that the climate problem requires a global solution, that Annex I and non-Annex I countries are mutually dependent on each other and that only cooperation regarding technology in combination with significant financial support will provide the chance to successfully tackle climate change.