Holocene flood frequency across the Central Alps – solar forcing and evidence for variations in North Atlantic atmospheric circulation

The frequency of large-scale heavy precipitation events in the European Alps is expected to undergo substantial changes with current climate change. Hence, knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections. We present a comprehensive Holocene (10,000 years) reconstruction of the flood frequency in the Central European Alps combining 15 lacustrine sediment records. These records provide an extensive catalog of flood deposits, which were generated by flood-induced underflows delivering terrestrial material to the lake floors. The multi-archive approach allows suppressing local weather patterns, such as thunderstorms, from the obtained climate signal. We reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high-altitude study sites do inhibit the generation of flood layers. We found that flood frequency was higher during cool periods, coinciding with lows in solar activity. In addition, flood occurrence shows periodicities that are also observed in reconstructions of solar activity from C-14 and Be-10 records (2500-3000, 900-1200, as well as of about 710, 500, 350, 208 (Suess cycle), 150, 104 and 87 (Gleissberg cycle) years). As atmospheric mechanism, we propose an expansion/shrinking of the Hadley cell with increasing/decreasing air temperature, causing dry/wet conditions in Central Europe during phases of high/low solar activity. Furthermore, differences between the flood patterns from the Northern Alps and the Southern Alps indicate changes in North Atlantic circulation. Enhanced flood occurrence in the South compared to the North suggests a pronounced southward position of the Westerlies and/or blocking over the northern North Atlantic, hence resembling a negative NAO state (most distinct from 4.2 to 2.4 kyr BP and during the Little Ice Age). South-Alpine flood activity therefore provides a qualitative record of variations in a paleo-NAO pattern during the Holocene. Additionally, increased South Alpine flood activity contrasts to low precipitation in tropical Central America (Cariaco Basin) on the Holocene and centennial time scale. This observation is consistent with a Holocene southward migration of the Atlantic circulation system, and hence of the ITCZ, driven by decreasing summer insolation in the Northern hemisphere, as well as with shorter-term fluctuations probably driven by solar activity. (C) 2013 Elsevier Ltd. All rights reserved.

Lake sediments as archives of recurrence rates and intensities of past flood events

Palaeoflood hydrology is an expanding field as the damage potential of flood and flood-related processes are increasing with the population density and the value of the infrastructure. Assessing the risk of these hazards in mountainous terrain requires knowledge about the frequency and severness of such events in the past. A wide range of methods is employed using diverse biologic, geomorphic or geologic evidences to track past flood events. Impact of floods are studied and dated on alluvial fans and cones using for example the growth disturbance of trees (Stoffel and Bollschweiler 2008; Schneuwly-Bollschweiler and Stoffel 2012: this volume) or stratigraphic layers deposited by debris flows, allowing to reconstruct past flood frequencies (Bardou et~al. 2003). Further downstream, the classical approach of palaeoflood hydrology (Kochel and Baker 1982) utilizes geomorphic indicators such as overbank sediments, silt lines and erosion features of floods along a river (e.g. Benito and Thorndycraft 2005). Fine-grained sediment settles out of the river suspension in eddies or backwater areas, where the flow velocity of the river is reduced. Records of these deposits at different elevations across a river’s profile can be used to assess the discharge of the past floods. This approach of palaeoflood hydrology studies was successfully applied in several river catchments (e.g. Ely et al. 1993; Macklin and Lewin 2003; O’Connor et al. 1994; Sheffer et al. 2003; Thorndycraft et al. 2005; Thorndycraft and Benito 2006). All these different reconstruction methods have their own advantages and disadvantages, but often these studies have a limited time coverage and the records are potentially incomplete due to lateral limits of depositional areas and due to the erosional power of fluvial processes that remove previously deposited flood witnesses. Here, we present a method that follows the sediment particle transported by a flood event to its final sink: the lacustrine basin.

Reconstruction of a flash flood with large wood transport and its influence on hazard patterns in an ungauged mountain basin

The reconstruction of past flash floods in ungauged basins leads to a high level of uncertainty, which increases if other processes are involved such as the transport of large wood material. An important flash flood occurred in 1997 in Venero Claro (Central Spain), causing significant economic losses. The wood material clogged bridge sections, raising the water level upstream. The aim of this study was to reconstruct this event, analysing the influence of woody debris transport on the flood hazard pattern. Because the reach in question was affected by backwater effects due to bridge clogging, using only high water mark or palaeostage indicators may overestimate discharges, and so other methods are required to estimate peak flows. Therefore, the peak discharge was estimated (123 ± 18 m3 s–1) using indirect methods, but one-dimensional hydraulic simulation was also used to validate these indirect estimates through an iterative process (127 ± 33 m3 s–1) and reconstruct the bridge obstruction to obtain the blockage ratio during the 1997 event (~48%) and the bridge clogging curves. Rainfall–Runoff modelling with stochastic simulation of different rainfall field configurations also helped to confirm that a peak discharge greater than 150 m3 s–1 is very unlikely to occur and that the estimated discharge range is consistent with the estimated rainfall amount (233 ± 27 mm). It was observed that the backwater effect due to the obstruction (water level ~7 m) made the 1997 flood (~35-year return period) equivalent to the 50-year flood. This allowed the equivalent return period to be defined as the recurrence interval of an event of specified magnitude, which, where large woody debris is present, is equivalent in water depth and extent of flooded area to a more extreme event of greater magnitude. These results highlight the need to include obstruction phenomena in flood hazard analysis.

A review of dendrogeomorphological research applied to flood risk analysis in Spain

Over the last forty years, applying dendrogeomorphology to palaeoflood analysis has improved estimates of the frequency and magnitude of past floods worldwide. This paper reviews the main results obtained by applying dendrogeomorphology to flood research in several case studies in Central Spain. These dendrogeomorphological studies focused on the following topics: (1) anatomical analysis to understand the physiological response of trees to flood damage and improve sampling efficiency; (2) compiling robust flood chronologies in ungauged mountain streams, (3) determining flow depth and estimating flood discharge using two-dimensional hydraulic modelling, and comparing them with other palaeostage indicators; (4) calibrating hydraulic model parameters (i.e. Manning roughness); and (5) implementing stochastic-based, cost–benefit analysis to select optimal mitigation measures. The progress made in these areas is presented with suggestions for further research to improve the applicability of dendrogeochronology to palaeoflood studies. Further developments will include new methods for better identification of the causes of specific types of flood damage to trees (e.g. tilted trees) or stable isotope analysis of tree rings to identify the climatic conditions associated with periods of increasing flood magnitude or frequency.

A new methodological protocol for the use of dendrogeomorphological data in flood risk analysis

Dendrogeomorphology uses information sources recorded in the roots, trunks and branches of trees and bushes located in the fluvial system to complement (or sometimes even replace) systematic and palaeohydrological records of past floods. The application of dendrogeomorphic data sources and methods to palaeoflood analysis over nearly 40 years has allowed improvements to be made in frequency and magnitude estimations of past floods. Nevertheless, research carried out so far has shown that the dendrogeomorphic indicators traditionally used (mainly scar evidence), and their use to infer frequency and magnitude, have been restricted to a small, limited set of applications. New possibilities with enormous potential remain unexplored. New insights in future research of palaeoflood frequency and magnitude using dendrogeomorphic data sources should: (1) test the application of isotopic indicators (16O/18O ratio) to discover the meteorological origin of past floods; (2) use different dendrogeomorphic indicators to estimate peak flows with 2D (and 3D) hydraulic models and study how they relate to other palaeostage indicators; (3) investigate improved calibration of 2D hydraulic model parameters (roughness); and (4) apply statistics-based cost–benefit analysis to select optimal mitigation measures. This paper presents an overview of these innovative methodologies, with a focus on their capabilities and limitations in the reconstruction of recent floods and palaeofloods.

The determinants of physician and pharmacist utilization and equity of access under Korean universal health insurance

This study examines the social and behavioral determinants of two types of primary care, seeing a physician or a pharmacist, for Koreans and evaluates the equity of the Korean national health insurance system. The study applies the Aday and Andersen access framework to cross-sectional data from the 1992 Korean National Health Interview Survey (N = 21,841).^ The study found that in Korea, the elderly were most likely, and children least likely, to have used physician services. Women, household heads, those in small families, and the less educated were more likely than their counterparts to use physician and pharmacist services. Health status and need were important determinants of Koreans seeing a doctor or a pharmacist. Differences in need substantially accounted for the original differences observed between subgroups. Resources associated with having insurance coverage, a regular source of care, and place of residence (rural/urban) ameliorated to some extent the subgroup differences in the use of physicians' and pharmacists' services among Koreans. They were also major independent predictors of access. Having insurance remains a particularly important predictor of who uses physician services. Among the insured, trade-offs in the use of physician and pharmacist services were found in the current system, i.e., uninsured and poor Koreans were more likely to use pharmacist services, while insured and rural Koreans were more likely to use doctor services. Among the insured, cost sharing rates are lower for physician than for pharmacist services. Self-employed persons were less likely than government and industrial workers to use physician services. An underlying expectation under universal health insurance was that the Korean health care system would be equitable. The research results, however, did not fully support this expectation.^ The policy implications of these findings are that measures are required to extend insurance coverage to the uninsured, to equalize differences in benefit packages between health plans, and to expand the availability of physicians in rural areas. Further research is also needed to understand those who do not currently have a regular source of care and why and the access barriers that may exist for selected demographic subgroups (those in large families and unmarried or divorced/widowed persons). ^

Source of health insurance and immunization rates: Findings from the 1996 Texas immunization survey

This study was a further investigation of the 1996 Texas Immunization Survey conducted by the Associateship for Disease Control and Prevention of the Texas Department of Health. The 1996 survey was conducted through 4,599 completed telephone interviews of families with a child between the ages of 3–35 months concerning the immunization status of Texas children. The present study determined differences in immunization rates for children aged 3–35 months for the last shot in the immunization series that should be completed before 2 years of age, a total of four shots, both overall and for different health insurance groups. Life tables were used to determine the percentage and distribution over time of completed vaccination rates for each shot. Emphasis was placed on the proportion of children that were immunized at the end of the recommended range of the immunization schedule, and at 2 years of age. Univariate and multivariate analysis was also performed in order to ascertain which risk factors predict whether or not a child will be immunized. RESULTS: Between 80–90% were immunized for the last shot of Hepatitis B; Measles, Mumps, and Rubella; and Polio at 2 years of age. Approximately 2/3 of the sample was immunized for Diphtheria, Pertussis, and Tetanus. Most of the children were immunized by the end of the recommended range of the immunization schedule except for Measles, Mumps, and Rubella. Children of parents with private indemnity insurance were significantly more likely to have received two of the four shots; children of uninsured parents were significantly less likely to have received three of the four shots. In multivariate analysis, maternal education was the only variable that consistently predicted immunization status for the different shots. Results indicate that a substantial gap exists for immunization rates between children with private insurance and uninsured children, despite recent policy changes to provide immunizations free of charge. Health care providers should pay extra attention to the poor and uninsured to make sure that all children receive timely immunizations. ^

Combining Wireless Sensor Networks and Machine Learning for Flash Flood Nowcasting

This paper addresses an investigation with machine learning (ML) classification techniques to assist in the problem of flash flood now casting. We have been attempting to build a Wireless Sensor Network (WSN) to collect measurements from a river located in an urban area. The machine learning classification methods were investigated with the aim of allowing flash flood now casting, which in turn allows the WSN to give alerts to the local population. We have evaluated several types of ML taking account of the different now casting stages (i.e. Number of future time steps to forecast). We have also evaluated different data representation to be used as input of the ML techniques. The results show that different data representation can lead to results significantly better for different stages of now casting.

Retrospective analysis of a nonforecasted rain-on-snow flood in the Alps – a matter of model limitations or unpredictable nature?

A rain-on-snow flood occurred in the Bernese Alps, Switzerland, on 10 October 2011, and caused significant damage. As the flood peak was unpredicted by the flood forecast system, questions were raised concerning the causes and the predictability of the event. Here, we aimed to reconstruct the anatomy of this rain-on-snow flood in the Lötschen Valley (160 km2) by analyzing meteorological data from the synoptic to the local scale and by reproducing the flood peak with the hydrological model WaSiM-ETH (Water Flow and Balance Simulation Model). This in order to gain process understanding and to evaluate the predictability. The atmospheric drivers of this rain-on-snow flood were (i) sustained snowfall followed by (ii) the passage of an atmospheric river bringing warm and moist air towards the Alps. As a result, intensive rainfall (average of 100 mm day-1) was accompanied by a temperature increase that shifted the 0° line from 1500 to 3200 m a.s.l. (meters above sea level) in 24 h with a maximum increase of 9 K in 9 h. The south-facing slope of the valley received significantly more precipitation than the north-facing slope, leading to flooding only in tributaries along the south-facing slope. We hypothesized that the reason for this very local rainfall distribution was a cavity circulation combined with a seeder-feeder-cloud system enhancing local rainfall and snowmelt along the south-facing slope. By applying and considerably recalibrating the standard hydrological model setup, we proved that both latent and sensible heat fluxes were needed to reconstruct the snow cover dynamic, and that locally high-precipitation sums (160 mm in 12 h) were required to produce the estimated flood peak. However, to reproduce the rapid runoff responses during the event, we conceptually represent likely lateral flow dynamics within the snow cover causing the model to react "oversensitively" to meltwater. Driving the optimized model with COSMO (Consortium for Small-scale Modeling)-2 forecast data, we still failed to simulate the flood because COSMO-2 forecast data underestimated both the local precipitation peak and the temperature increase. Thus we conclude that this rain-on-snow flood was, in general, predictable, but requires a special hydrological model setup and extensive and locally precise meteorological input data. Although, this data quality may not be achieved with forecast data, an additional model with a specific rain-on-snow configuration can provide useful information when rain-on-snow events are likely to occur.

Heterogeneous Beliefs and the Demand for D&O Insurance by Listed Companies

This paper introduces a new rationale for the existence of “Directors’ and Officers’” (D&O) insurance. We use a model with volatile stock markets where shareholders design compensation schemes that incentivize managers to stimulate short-term increases in stock prices that do not maximize long run stock market value. We show that D&O insurance provides a convenient instrument for the initial shareholders of a company to take advantage of differences in beliefs between insiders and outsiders in capital markets. The empirical results support the idea that both the insurance coverage and the premium are higher in the presence of new shareholders and volatile markets. The results prove robust in various empirical model specifications.

Predictors of Weight Loss Maintenance following an Insurance-Sponsored Weight Management Program

Intentional weight loss among overweight and obese adults (body mass index ≥ 25 kg/m2) is associated with numerous health benefits, but weight loss maintenance (WLM) following participation in weight management programming has proven to be elusive. Many individuals attempting to lose weight join formal programs, especially women, but these programs vary widely in focus, as do postprogram weight regain results. We surveyed 2,106 former participants in a community-based, insurance-sponsored weight management program in the United States to identify the pre, during, and post-intervention behavioral and psychosocial factors that lead to successful WLM. Of 835 survey respondents (39.6% response rate), 450 met criteria for inclusion in this study. Logistic regression analyses suggest that interventionists should assess and discuss weight loss and behavior change perceptions early in a program. However, in developing maintenance plans later in a program, attention should shift to behaviors, such as weekly weighing, limiting snacking in the evening, limiting portion sizes, and being physically active every day.

A physical approach on flood risk vulnerability of buildings

The design of efficient hydrological risk mitigation strategies and their subsequent implementation relies on a careful vulnerability analysis of the elements exposed. Recently, extensive research efforts were undertaken to develop and refine empirical relationships linking the structural vulnerability of buildings to the impact forces of the hazard processes. These empirical vulnerability functions allow estimating the expected direct losses as a result of the hazard scenario based on spatially explicit representation of the process patterns and the elements at risk classified into defined typological categories. However, due to the underlying empiricism of such vulnerability functions, the physics of the damage-generating mechanisms for a well-defined element at risk with its peculiar geometry and structural characteristics remain unveiled, and, as such, the applicability of the empirical approach for planning hazard-proof residential buildings is limited. Therefore, we propose a conceptual assessment scheme to close this gap. This assessment scheme encompasses distinct analytical steps: modelling (a) the process intensity, (b) the impact on the element at risk exposed and (c) the physical response of the building envelope. Furthermore, these results provide the input data for the subsequent damage evaluation and economic damage valuation. This dynamic assessment supports all relevant planning activities with respect to a minimisation of losses, and can be implemented in the operational risk assessment procedure.

Hochwasser-«Katastrophen» in Basel vom 13. bis 21. Jahrhundert Rekonstruktion, Deutung und Lerneffekte

Magnitudes of peak discharges of 43 non-instrumentally measured Rhine river floods at Basel were reconstructed. The methodology is based on a range of different historic sources, containing flood information (including traditional urban inundation reference points from flood reports of medieval and early modern period chroniclers as well as 19th century journalists, flood marks, paintings and drawings, town maps, longitudinal and cross profiles etc.). These traditional pre-instrumental “flood information systems” still existed in the 19th century, when in 1808 the first instrumental hydrological measurements started. They thus could be calibrated with instrumental measurements in the 19th century overlapping period. The result is a 743 year long quantified Rhine river flood series. Floods of both periods (pre-instrumental as well as instrumental) can thus be directly compared for the very first time. The long-range consequences of rivers Kander and Aare deviations in 1714 and 1878 are reflected in a distinct change of magnitudes of peak discharges in Basel. A clear flood “disaster gap” appears in the 20th century. The lack of any extreme floods for such a long time is completely unique during the 743-year period of analysis. This result will influence the statistical assessment of once-in-a-century events, which might be of great interest for insurance campanies.