Risk Analysis | Year: 2013
Many attempts are made to assess future changes in extreme weather events due to anthropogenic climate change, but few studies have estimated the potential change in economic losses from such events. Projecting losses is more complex as it requires insight into the change in the weather hazard but also into exposure and vulnerability of assets. This article discusses the issues involved as well as a framework for projecting future losses, and provides an overview of some state-of-the-art projections. Estimates of changes in losses from cyclones and floods are given, and particular attention is paid to the different approaches and assumptions. All projections show increases in extreme weather losses due to climate change. Flood losses are generally projected to increase more rapidly than losses from tropical and extra-tropical cyclones. However, for the period until the year 2040, the contribution from increasing exposure and value of capital at risk to future losses is likely to be equal or larger than the contribution from anthropogenic climate change. Given the fact that the occurrence of loss events also varies over time due to natural climate variability, the signal from anthropogenic climate change is likely to be lost among the other causes for changes in risk, at least during the period until 2040. More efforts are needed to arrive at a comprehensive approach that includes quantification of changes in hazard, exposure, and vulnerability, as well as adaptation effects. © 2012 Society for Risk Analysis.
Journal of Flood Risk Management | Year: 2014
Within the context of the Dutch Delta Programme, economically efficient flood protection standards for the entire Netherlands were calculated using a recently developed methodology for cost-benefit analysis and up-to-date insights into flood risk assessment. This results in economically efficient flood protection standards for different parts of the Netherlands that significantly differ from current legal flood protection standards. The cost-benefit analysis shows that it is economically efficient to raise protection standards especially along the rivers Rhine and Meuse, while for many dike ring areas in the coastal region, existing legal flood protection standards seem relatively high. An additional Monte Carlo analysis shows that in light of many uncertainties, these are also robust conclusions. The cost-benefit analysis does not support a general increase of the legal flood protection standards for all flood-prone areas in the Netherlands by (at least) a factor 10, as was recommended by the (second) Delta Committee in 2008. © 2012 The Chartered Institution of Water and Environmental Management (CIWEM) and John Wiley & Sons Ltd.
Van der Westhuysen A.J.,Deltares
Coastal Engineering | Year: 2012
Hindcast studies for the Dutch Wadden Sea using the spectral wind wave model SWAN have shown the significant influence of currents on wave predictions in the tidal inlets. In a number of cases with strong gradients in opposing, partially blocking current, wave heights are significantly overestimated. Ris and Holthuijsen (1996) propose that such overestimations are due to insufficient steepness dissipation of waves on an opposing current gradient. The present paper presents a new formulation for the enhanced breaking dissipation of waves on negative current gradients (accelerating opposing current; decelerating following current). Nonlinear effects are not included in detail for these partial blocking conditions, but handled parametrically. Unlike the expression by Ris and Holthuijsen (1996), the proposed expression isolates the steepening effect of the current gradient on the waves, so that inherently steep young wind sea is not overly dissipated. This expression contains one additional unknown parameter, which was calibrated using laboratory observations. Validation of this enhanced dissipation term for field cases of the Amelander Zeegat tidal inlet (Dutch Wadden Sea) shows an improvement in the tidal channel for both opposing and following current situations with negative gradients. In particular, the results for the young wind sea on the tidal flats are not significantly affected, as desired, unlike with the expression of Ris and Holthuijsen (1996). However, since the remaining dissipation terms in SWAN have been calibrated without this enhanced dissipation term, the addition of the proposed formulation results in some deterioration of the overall statistics. © 2012 Elsevier B.V.
Page S.E.,University of Leicester |
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2016
Peatlands are a significantcomponent of the global carbon (C) cycle, yet despite their role as a long-term C sink throughout the Holocene, they are increasingly vulnerable to destabilization. Nowhere is this shift from sink to source happening more rapidly than in Southeast Asia, and nowhere else are the combined pressures of land-use change and fire on peatland ecosystem C dynamics more evident nor the consequences more apparent. This review focuses on the peatlands of this region, tracing the link between deforestation and drainage and accelerating C emissions arising from peat mineralization and fire. It focuses on the implications of the recent increase in fire occurrence for air quality, human health, ecosystem resilience and the global C cycle. The scale and controls on peat-driven C emissions are addressed, noting that although fires cause large, temporary peaks in C flux to the atmosphere, year-round emissions frompeat mineralization are of a similarmagnitude. The reviewconcludes by advocating land management options to reduce future fire risk as part of wider peatland management strategies, while also proposing that this region’s peat fire dynamic could become increasingly relevant to northern peatlands in a warming world. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
Van Der Westhuysen A.J.,Deltares
Journal of Geophysical Research: Oceans | Year: 2010
Recent studies have shown that the spectral wind wave model SWAN (Simulating Waves Nearshore) underestimates wave heights and periods in situations of finite depth wave growth. In this study, this inaccuracy is addressed through a rescaling of the Battjes and Janssen (1978) bore-based model for depth-induced breaking, considering both sloping bed surf zone situations and finite depth wave growth conditions. It is found that the variation of the model error with the breaker index γBJ in this formulation differs significantly between the two types of conditions. For surf zones, clear optimal values are found for the breaker index. By contrast, under finite depth wave growth conditions, model errors asymptotically decrease with increasing values of the breaker index (weaker dissipation). Under both the surf zone and finite depth wave growth conditions, optimal calibration settings of γBJ were found to correlate with the dimensionless depth k pd (where kp is the spectral peak wave number and d is the water depth) and the local mean wave steepness. Subsequently, a new breaker index, based on the local shallow water nonlinearity, expressed in terms of the biphase of the self-interactions of the spectral peak, is proposed. Implemented in the bore-based breaker model of Thornton and Guza (1983), this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations. Hence, the proposed expression yields a significant improvement in model accuracy over the default Battjes and Janssen (1978) model for finite depth growth situations, while retaining good performance for sloping bed surf zones. © 2010 by the American Geophysical Union.