Neil Macdonald

Changing climate shifts timing of European floods

Flooding along the river Will a warming climate affect river floods? The prevailing sentiment is yes, but a consistent signal in flood magnitudes has not been found. Blöschl et al. analyzed the timing of river floods in Europe over the past 50 years and found clear patterns of changes in flood timing that can be ascribed to climate effects (see the Perspective by Slater and Wilby). These variations include earlier spring snowmelt floods in northeastern Europe, later winter floods around the North Sea and parts of the Mediterranean coast owing to delayed winter storms, and earlier winter floods in western Europe caused by earlier soil moisture maxima. Science, this issue p. 588 see also p. 552 Climate change is affecting the timing of river flooding across Europe. A warming climate is expected to have an impact on the magnitude and timing of river floods; however, no consistent large-scale climate change signal in observed flood magnitudes has been identified so far. We analyzed the timing of river floods in Europe over the past five decades, using a pan-European database from 4262 observational hydrometric stations, and found clear patterns of change in flood timing. Warmer temperatures have led to earlier spring snowmelt floods throughout northeastern Europe; delayed winter storms associated with polar warming have led to later winter floods around the North Sea and some sectors of the Mediterranean coast; and earlier soil moisture maxima have led to earlier winter floods in western Europe. Our results highlight the existence of a clear climate signal in flood observations at the continental scale.

Reassessment of flood frequency using historical information for the River Ouse at York, UK (1200–2000)

Abstract The reassessment of flood risk at York, UK, is pertinent in light of major flooding in November 2000, and heightened concerns of a perceived increase in flooding nationally. Systematic flood level readings from 1877 and a wealth of documentary records dating back as far as 1263 AD give the City of York a long and rich history of flood records. This extended flood record provides an opportunity to reassess estimates of flood frequency over a time scale not normally possible within flood frequency analysis. This paper re-evaluates flood frequency at York, considering the strengths and weaknesses in estimates resulting from four contrasting methods of analysis and their corresponding data: (a) single-site analysis of gauged annual maxima; (b) pooled analysis of multi-site gauged annual maxima; (c) combined analysis of systematic annual maxima augmented with historical peaks, and (d) analysis of only the very largest peaks using a Generalized Pareto Distribution. Use of the historical information was found to yield risk estimates which were lower and considered to be more credible than those achieved using gauged records alone. Citation Macdonald, N. & Black, A. R. (2010) Reassessment of flood frequency using historical information for the River Ouse at York, UK (1200–2000). Hydrol. Sci. J. 55(7), 1152–1162.

Trends in flood seasonality of the River Ouse (Northern England) from archive and instrumental sources since AD 1600

The last decade has witnessed an increase in the application of historical records (historical and documentary) in developing a more complete understanding of high-magnitude flood frequency; but little consideration has been given to the additional information that documentary accounts contain, particularly relating to flood seasonality. This paper examines the methods and approaches available in long-term flood seasonality analysis and applies them to the River Ouse (Yorkshire) in Northern England since AD 1600. A detailed historical flood record is available for the City of York consisting of annual maxima flood levels since AD 1877, with documentary accounts prior to this. A detailed analysis of long-term flood seasonality requires confidence in the accuracy and completeness of flood records; as a result the augmented flood series are analysed using three strategies: firstly, considering all recorded floods since AD 1600; secondly, through detailed analysis of the more complete record since AD 1800; and finally, applying a threshold to focus on high-magnitude flood events since AD 1800. The results identify later winter flooding, particularly in the second half of the twentieth century, with a notable reduction in summer flood events at York during the twentieth century compared to previous centuries. Flood generating mechanisms vary little between the periods considered, with a general pattern of stability in the ratio of floods incorporating a snowmelt component.

The significance of Gilbert F. White’s 1945 paper ‘Human adjustment to floods’ in the development of risk and hazard management:

Few publications may claim to have transcended the original field in which they were written, by shaping a wide range of research areas and philosophies. In this short paper we reflect on the manner in which Gilbert F. White’s 1945 publication ‘Human adjustment to floods’ has not only shaped how we study and perceive flooding, but has also had a significance beyond its original aims, revolutionizing the ways in which hazard and risk are conceptualized more generally. Before considering the impact of ‘Human adjustment to floods’, we briefly review academic understanding of floods in the decades leading up to the 1940s and later place the 1945 paper in the context of White’s subsequent contributions to research which both developed and built on his ideas.

Current understanding of hydrological processes on common urban surfaces

Understanding the rainfall-runoff behaviour of urban land surfaces is an important scientific and practical issue as storm water management policies increasingly aim to manage flood risk at local scales within urban areas, whilst controlling the quality and quantity of runoff that reaches receiving water bodies. By reviewing field measurements reported within the literature on runoff, infiltration, evaporation and storage on common urban surfaces, this study describes a complex hydrological behaviour with greater rates of infiltration than often assumed, contradicting a commonly adopted, but simplified classification of the hydrological properties of urban surfaces. This shows that the term impervious surface, or impermeable surface, referring to all constructed surfaces (e.g. roads, roofs, footpaths, etc.) is inaccurate and potentially misleading. The hydrological character of urban surfaces is not stable through time, with both short (seasonal) and long term (decadal) changes in hydrological behaviour, as surfaces respond to variations in seasonal characteristics and degradation in surface condition. At present these changing factors are not widely incorporated into hydrological modelling or urban surface water management planning, with static values describing runoff and assumptions of imperviousness often used. Developing a greater understanding of the linkages between urban surfaces and hydrological behaviour will improve the representation of diverse urban landscapes within hydrological models.

Hydrological thresholds and basin control over paleoflood records in lakes

The scarcity of long-term hydrological data is a barrier to reliably determining the likelihood of floods becoming more frequent and/or intense in a warmer world. Lake sediments preserve characteristic event layers, offering the potential to develop widely distributed and unique chronologies of historical floods. Inferring flood magnitude remains a greater challenge, previously overcome in part by analyzing sharply laminated polar or alpine sequences. Here we demonstrate an approach to obtain flood frequency and magnitude data from an unexploited resource, the largely visually homogeneous, organic sediments that typify most temperate lakes. The geochemical composition and end-member modeling of sediment trap and adjacent short core particle size data for Brotherswater (northwest England) discriminates the signature of infrequent, coarse-grained flood deposits from seasonal and longer term allogenic (enhanced discharge and sediment supply during winter) and autogenic (summer productivity, thermal mixing) depositional processes. Comparing the paleoflood reconstruction to local river discharges shows that hydrological thresholds censor event signature preservation, with 4 yr recurrence intervals detectable in delta-proximal sediments declining to 9 yr in the lake center. Event threshold (discharge) and process characterization are essential precursors to discerning flood magnitude from sediment archives. Implementation of our approach in globally prevalent temperate lakes offers a vast, unique repository of long-term hydrological data for hydrologists, climate modelers, engineers, and policy makers addressing future flood risks.

A 2D MODEL OF WAVES AND UNDERTOW IN THE SURF ZONE

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Examining the social consequences of extreme weather: the outcomes of the 1946/1947 winter in upland Wales, UK

Extreme forms of weather are predicted to become more frequent experiences in the future. However, the hardest event to mitigate against is the unexpected. In the UK, the occurrence of winter snowfall is difficult to predict, highly variable, both spatially and temporally and predicted to become less common in the future. This paper examines the consequences of the severe winter of 1946/1947 at the local scale through a Welsh case study of Cwm Tywi, a community of upland sheep farms. This community had shown great resilience during the snowiest winter on record in comparison with other, more urban communities, but the inhabitants eventually abandoned their homes because of the emotional distress caused by the loss of a large proportion of the livestock. In addition to the severity of the snow, perceptions of the extreme nature of this event and the community’s ability to mitigate as a result of rurality, self-sufficiency and remoteness are investigated through the analysis of interviews, oral histories, and other documentary accounts. This case study provides an insight into the complexity of understanding vulnerability, adaptation and resilience, which are temporally and spatially specific.

Reconstructed annual precipitation series for Scotland (1861 – 1991): Spatial and temporal variations, and links to the atmospheric circulation

Abstract This paper constructs annual homogenised precipitation series for 13 locations in Scotland (1861 – 1991) from non-standard sources. Whilst the British Rainfall series represents the backbone of most UK rainfall records before the middle of the twentieth century, this paper returns to the original records to examine spatial and temporal variations in Scottish precipitation. The records were subjected to trend analysis and principal components analysis (PCA), and then related to atmospheric circulation parameters to understand the synoptic-scale mechanisms involved. Upward (downward) trends in precipitation were noted in western (eastern) Scotland over the period 1870 – 1991. Precipitation variability in western (eastern) Scotland is best explained by fluctuations in the westerly circulation (pressure), with the west-east precipitation gradient closing in those years with below average pressure, and a greater frequency of northerly and/or easterly winds. Precipitation trends cannot be explained by changes in atmospheric circulation patterns, suggesting that other factors must be involved.

The inclusion of sustainable drainage systems in flood management in the post‐industrial city: A case study of Glasgow

Abstract The management of urban stormwater and flooding is challenging, particularly within older, post‐industrial urban environments where infrastructure, housing and businesses already operate. The urban environment constrains opportunities for the development and integration of new approaches to drainage management, particularly the use of sustainable drainage systems (SuDS). These issues are investigated through a case study of Glasgow. The northeast of the city suffered significant urban flooding in July 2002 following an intense con‐vective summer storm. This event overloaded the urban drainage system, which was heavily integrated and led to the back flow of foul water into streets and homes. This study examines the response to this event and the construction of an integrated drainage management plan for the city, the Glasgow Strategic Drainage Plan (GSDP), which includes greater use of SuDS in tackling the citys capacity problems. Reflecting on the interdisciplinary nature of urban drainage management, this study adopts a social science method, undertaking semi‐structured interviews with key actors involved in producing the GSDP.