2.2 Observed event Ewc estimates from forest plot studies
in temperate locations
Studies relevant to UK conditions with forest plot CWB Ewcobservations were identified. Relevant studies were defined
climatologically using the revised Köppen climate classification (Chen
& Chen, 2013) with the recognition that the classification provides
general climatic classes within which there is a large degree of
variability. Although this variability exists, Köppen climate
classifications were used with the rationale that hydrometerological
conditions will have similarities to those of UK mountainous regions
during large and extreme rainfall events. The specific classifications
deemed acceptable for the purposes of this study were: Cfa (mild
temperate; fully humid; hot summer), Cfb (mild temperate; fully humid;
warm summer), Cfc (mild temperate; fully humid; cool summer), Csb (mild
temperate; dry summer; warm summer), Dfb (snow; fully humid; warm
summer), Dfc (snow; fully humid; cool summer), Dfd (snow; fully humid;
cold summer): the classifications Cfb and Cfc encompass all mountainous
regions of the UK. For the climate classes where snow can form a
significant part of winter precipitation (i.e. Dfb, Dfc and Dfd), care
was taken not to include data affected by snow falls: in most cases this
was already carried out in the original study.
From the studies identified as relevant (Table Supp. 1), only CWBEwc observations reported on a rainfall event basis or as a daily
total were collated for analyses. For consistency, events reported to be
over 24 hours (but no more than 48 hours) duration were standardised by
calculating a normalised 24-hour rainfall (i.e.\(Pg=\ 24\left(\frac{\text{Pe}}{\text{De}}\right)\)) wherePe is the total event precipitation and De is
event duration in hours): note that, in the text below, 𝑃𝑔 relates to a
daily or normalised daily total rainfall unless otherwise stated. It is
accepted that using daily observations is somewhat artificial in as much
as the duration of rainfall events may be truncated where they span
multiple days; it is also recognised that both daily and event data may
include periods without rain. Event-based data where event duration was
not reported were also collated and are presented separately.
Data were gathered using values provided in tables or by digitising data
presented as figures in published material and by abstracting data from
field log sheets; in the case of Aussenac (1968) and Reynolds and
Henderson (1967) Pg-Ewc relationships were digitised.
Where observations were obtained from digitised figures, and where there
were many data points, obscured or overlapping data will have resulted
in some values not being included; these data were, however, invariably
for relatively low 𝑃𝑔 magnitudes. In some cases, the dates associated
with individual rainfall events were not provided in the published
material, which does not allow separation by season (or by leafed or
leafless period for deciduous species). Furthermore, as event data were
limited and data for deciduous forest plots were very few, all events
irrespective whether they were evergreen or deciduous were combined for
the comparison with theoretical estimates, but are identified separately
in figures.