New paper finds 'strong correlation between floods and solar magnetic activity', no trend in British floods

A new paper under discussion for Hydrology and Earth System Sciences finds recent floods in Britain are "not exceptional," "there appears to be no shift in long term flood frequency," and 

"The principal finding of this work is that of the strong correlation between flood-rich phases and solar magnetic activity."

According to the author,

"The findings identify that whilst recent floods are notable, several comparable periods of increased flooding are identifiable historically, with periods of greater frequency (flood-rich periods) or/and larger floods. The use of historical records identifies that the largest floods often transcend single catchments affecting regions and that the current flood rich period is not exceptional."

The paper joins many others in the scientific literature linking the hydrological cycle, precipitation, floods & droughts to solar activity, one of many solar amplification mechanisms described in the literature. 

Excerpt:

Summary

The apparent increase in flooding witnessed over the last decade appears in consideration of the long term flood record to be unexceptional, whilst the period since 2000 is considered as flood-rich, the period 1970–2000 is relatively “flood poor”, which may partly explain why recent floods are often perceived as extreme events. The much publicised (popular media) apparent change in flood frequency since 2000 may reflect natural variability, as there appears to be no shift in long term flood frequency (Fig. 4). In reviewing the flood series for European systems for which long flood series have been reconstructed, a complex picture is identified, whilst flood rich phases appear synchronous across many systems (ca. 1600 and 1765–1780), others show less synchronicity (1920s), whilst a number of prominent flood-rich phases at a European scale appear subdued or are not evident in the British FI (e.g. ca. 1740–1750). 

The principal finding of this work is that of the strong correlation between flood-rich phases and solar magnetic activity, indicating a clear driver for flooding patterns across Britain, what is still unclear is the relationship between the spatial/temporal distribution of flood clusters and solar activity. This work suggests that flood-rich periods relate to both positive and negative NAOI, with reasonable correspondence with previously diagnosed periods of climatic variability identified from individual series from across Europe. The inclusion of historical flood information provides a better understanding of long-term flood patterns. The detection of flood-rich periods and attribution to periods of climatic change are tentative. The historical records still hold a wealth of untapped information within the records for which specific discharges cannot be estimated, but from which indices could be extracted (Barriendos and Coeur, 2004). The wealth of information presented by the historical records presents valuable new information for flood risk assessment and management (Kjeldsen et al., 2014); as new flood chronologies become available, more detailed and complete indices based chronologies will improve the resolution and enhancing understanding of flood-rich and -poor periods, presenting a more complete depiction of the role of climate and extreme floods.

Hydrol. Earth Syst. Sci. Discuss., 11, 10157-10178, 2014 www.hydrol-earth-syst-sci-discuss.net/11/10157/2014/ doi:10.5194/hessd-11-10157-2014 Millennial scale variability in high magnitude flooding across Britain

N. Macdonald
Department of Geography and Planning, University of Liverpool, Liverpool, L69 7ZT, UK
Abstract. The last decade has witnessed severe flooding across much of the globe, but have these floods really been exceptional? Globally, relatively few instrumental river flow series extend beyond 50 years, with short records presenting significant challenges in determining flood risk from high-magnitude floods. A perceived increase in extreme floods in recent years has decreased public confidence in conventional flood risk estimates; the results affect society (insurance costs), individuals (personal vulnerability) and companies (e.g. water resource managers – flood/drought risk). Here we show how historical records from Britain have improved understanding of high magnitude floods, by examining past spatial and temporal variability. The findings identify that whilst recent floods are notable, several comparable periods of increased flooding are identifiable historically, with periods of greater frequency (flood-rich periods) or/and larger floods. The use of historical records identifies that the largest floods often transcend single catchments affecting regions and that the current flood rich period is not exceptional.

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Also published today in the same journal, a paper finding cold periods such as the Little Ice Age were associated with increased extreme precipitation and flooding, the opposite of climate model assumptions. 

Hydrol. Earth Syst. Sci. Discuss., 11, 10085-10116, 2014 www.hydrol-earth-syst-sci-discuss.net/11/10085/2014/ doi:10.5194/hessd-11-10085-2014 Documentary evidence of historical floods and extreme rainfall events in Sweden 1400–1800

D. Retsö
Dept. of Economic History, Stockholm University, 10691 Stockholm, Sweden
Abstract. This article explores documentary evidence of floods and extreme rainfall events in Sweden in the pre-instrumental period (1400–1800). The survey shows that two subperiods can be considered as flood-rich, 1590–1670 and the early 18th century. The result is related to a low degree of human impact on hydrology during the period, and suggest that climatic factors, such as lower temperatures and increased precipitation connected to the so called Little Ice Age, should be considered as the main driver behind flood frequency and magnitude.