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# Conference Report 1st European Hail Workshop

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## Abstract

The 1st European Hail workshop took place in Bern in June 2014. The workshop was organized into five topical session i) Convection and hail in a changing climate, ii) Microphysics and dynamics of hailstorms, iii) Hail damage and hail damage prevention, iv) Local probabilities and long-term statistics of hail, and v) Nowcasting and forecasting of hail. This report summarizes the scientific contributions presented and the open scientific questions discussed at the workshop. Available: http://www.schweizerbart.de/papers/metz/detail/24/84733/Conference_Report_1st_European_Hail_Workshop?l=EN
BMeteorologische Zeitschrift,Vol.24, No. 4, 441–442 (published online April 13, 2015) Conference Paper
Conference Report 1st European Hail Workshop
Olivia Martius1, Michael Kunz3, Luca Nisi1,2and Alessandro Hering2
1Oeschger Centre for Climate Change Research, Mobiliar Lab for Natural Risks and Institute of Geography,
University of Bern, Switzerland
2MeteoSwiss, Radar, Satellite and Nowcasting division, Locarno-Monti, Switzerland
3Institute for Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology, Germany
(Manuscript received January 9, 2015; in revised form March 6, 2015; accepted March 16, 2015)
Abstract
The 1st European Hail workshop took place in Bern in June 2014. The workshop was organized into ﬁve
topical session i) Convection and hail in a changing climate, ii) Microphysics and dynamics of hailstorms,
iii) Hail damage and hail damage prevention, iv) Local probabilities and long-term statistics of hail, and
v) Nowcasting and forecasting of hail. This report summarizes the scientiﬁc contributions presented and the
open scientiﬁc questions discussed at the workshop.
Keywords: hail
Introduction
In recent years, hail damage has increased substantially
in several European regions. Despite the high damage
potential of large hail in the order of billions of Euros,
knowledge on hail frequency, microphysical processes
and temporal variability is still limited. To foster the sci-
entiﬁc exchange on this topic, the Oeschger Centre for
Climate Change Research (OCCR), the Karlsruhe Insti-
tute of Technology (KIT), the Mobiliar Lab, and Meteo-
Swiss jointly organized the 1st European Hail Workshop,
which took place at the University of Bern from 25 to
27 June 2014. The overall aim of the workshop was
to bring together scientists working on hail-related re-
search questions as well as practitioners from the oper-
ational weather forecast community and from the insur-
ance industry. The topical scope was intentionally very
broad ranging from fundamental research topics to var-
ious application aspects. The workshop – attended by
more than 130 participants from 18 different countries
and from 21 different operational weather services – was
structured into the following ﬁve thematic sessions:
Convection and hail in a changing climate
Microphysics and dynamics of hailstorms
Hail damage and hail damage prevention
Local probabilities and long-term statistics of hail
Nowcasting and forecasting of hail
The detailed program of the workshop and PDFs of most
of the presentations and posters, as well as a recording
of the Nowcasting and Forecasting session are available
from the following website:
http://www.oeschger.unibe.ch/events/conferences/hail/
programme_en.html
Corresponding author: Olivia Martius, Oeschger Centre for Climate Change
Research, Mobiliar Lab for Natural Risks and Institute of Geography, Univer-
sity of Bern, Switzerland, Hallerstrasse 12, 3012 Bern, Switzerland, e-mail:
Olivia.martius@giub.unibe.ch
Convection and hail in a changing
climate
The workshop opened with contributions focusing on
the important topic of convection and hail in a changing
climate, which underlined the big research gap that is
still present in this ﬁeld of research. The scarce availabil-
ity of reliable long-term information of hail frequency
on the ground hampers the analysis of possible trends in
recent decades. Further on, there is a stark mismatch of
scales between the spatial resolution of state-of-the-art
climate model projections and the scale of the processes
that result in severe convection and hail.
One approach to tackle this problem is to identify the
meso-scale to synoptic-scale environment(s) beneﬁcial
for hailstorm formation and to use these parameters as
proxies for hail in reanalysis or climate model data. Cor-
responding analyses are performed based on local ob-
servations (e.g., sounding data) and gridded re-analysis
and climate model data sets (presentations by Sanderson
et al., Zhang and Li, Mohr and Kunz, Manzato, Pucik
et al., Stoll and Jordi). This approach, however, currently
does not include effects of changing aerosol concentra-
tions or changes in the microphysical processes.
Microphysics and dynamics of
hailstorms
Current challenges in modeling the microphysical pro-
cesses involved in hail formation and melting include
the diversity of ice nuclei (presentation by Hoose), the
representation of internally mixed (partly frozen – partly
liquid) hailstones and their properties (e.g., spongy ice)
(presentations by List, Sant and Seifert), and the fall
speed and terminal velocity of hail and graupel (presen-
tation by Heymsﬁeld and Wright). These challenges can
be addressed through combined efforts in model devel-
opment and high-quality in-situ and laboratory measure-
ments. The further development of improved hail micro-
DOI 10.1127/metz/2015/0667 Gebrüder Borntraeger Science Publishers, Stuttgart, www.borntraeger-cramer.com
442 O. Martius et al.: Conference Report 1st European Hail Workshop Meteorol. Z., 24, 2015
physics schemes is also of central importance for numer-
ical weather prediction (NWP) activities (presentations
by Milbrandt and Martynov et al.).
Hail damage and hail damage prevention
A detailed understanding of the microphysical proper-
ties of hail is also the basis for hail suppression at-
tempts. Several hail suppression programs, mainly run
in agriculture intensive areas, using aircraft or ground-
based systems for seeding with silver-iodide were pre-
sented at the workshop (presentations by Foris, Teschl
et al., Berthet and Dessens). All programs include a
combination of hailstorm nowcasting and monitoring
activities, insurance solutions and hail suppression tech-
niques. These programs provide some of the longest ob-
servations of hail occurrence and hailstone properties in
Europe.
Insurance companies have reported on increasing
trends in hail losses to properties and vehicles in re-
cent decades. The current focus is on the development of
sophisticated hail loss models (presentations by Geiss-
bühler and Ritz, Griesser et al., Schmidberger et al., Vic-
tor et al.). Challenges faced when constructing the loss
models include (i) a lack of direct observational data
(e.g., on hailstone sizes and shapes), (ii) the complex-
ity of the vulnerability of buildings and constructions to
hail (e.g., residential, industrial and commercial build-
ings), and (iii) consideration of the time of the year
(e.g., mature vs. premature crops) and of human ac-
tions (e.g., closing of window blinds) (presentations by
Imhof and Choffet, Heidemann). Hail loss models ap-
ply statistical methods to increase the number of severe
hail swaths beyond available observations (presentations
by Schmidberger et al., Geissbühler and Ritz, Griesser
et al.).
Local probabilities and long-term
statistics of hail
The statistical approach used for hail loss models is
complementary to a series of hail frequency climatolo-
gies that are currently being established in many coun-
tries, mainly based on single polarization radar observa-
tions covering the last 10 to 20 years (presentations by
Nisi et al., Meyer et al., Kunz et al., Lukach and Delobbe,
Rigo et al., Pocakal, Stolaki, Schemm et al.). Using such
data sets requires ground observations (e.g., hail pads,
insurance loss data) for calibration and veriﬁcation. Ad-
ditional observations are provided, for example, by the
comprehensive archive of the European Severe Weather
Database (ESWD, Dotzek et al., 2009, presentation by
Groenemeijer et al.) that collects hail reports from vol-
untary observers and weather services. Also relying on
voluntary hail reports is the crowdsourcing mPing smart
phone citizen science project, currently established in
the US (Elmore et al., 2014).
Nowcasting and forecasting of hail
The need for and importance of reliable ground obser-
vations have been underlined from the research commu-
nity, the insurance industry, but also from the weather
services. These observations are required for model cal-
ibration and veriﬁcation of radar- and numerical weather
prediction (NWP) model-based nowcasting tools, but
also for developing and extending radar-based hail prod-
ucts including new dual-polarization products. Now-
casting methods combine radar information with NWP
model output and statistical tools to provide partially
fully-automated hail warnings on time-scales from min-
utes up to a few hours (presentations by Hering et al.,
Auer et al., Winterrath, Kaltenboeck and Ryzhkov).
Nowcasting includes the tracking of hail cells and a pre-
diction of their path. Besides radar data other sources of
remote sensing information such as lightning- (poster by
Rigo and Pineda, presentations by Betz and Moehrlein,
Jurkovic and Mahovic, Schmid) and satellite-based es-
timates of effective radii have proven valuable for now-
casting purposes. Polarimetric radars, ﬁnally, offer the
potential to provide further information on the hailstone
size (e.g., Ryzhkov et al. 2013) and shape distribution
and falling behavior, but this still needs some veriﬁca-
tion (presentation by Lakshmanan).
Summary
The workshop demonstrated the valuable collaboration
between research and business in a ﬁeld with scarce data
availability. Research efforts in the next couple of years
should be dedicated to increase the quantity and quality
of hail observations. These efforts will be a combination
of rescuing and processing available data and exploit-
ing new data collection opportunities and new observ-
ing systems (e.g., automatic hail sensors, presentation by
Löfﬂer-Mang et al.). These data sets will be the founda-
tion for improved nowcasting and forecasting systems of
hail, for improved process understanding and the devel-
opment of novel microphysical schemes for NWP and
climate models, as well as for long-term hail frequency
and trend studies.
Acknowledgements
The organization committee would like to thank the
Mobiliar Lab for Natural Risks for substantial ﬁnancial
support and the Oeschger Centre for Climate Change
Research for administrative and logistic support. We
thank Hannes Sutter,Monika Wälti,andMichael
Rifﬂer for providing expert logistic support.
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... Hailstorms are local and rare events which cause high damages and economic losses to human infrastructure and agriculture in Central Europe (Martius et al. 2015;Munich Re 2007). It should be noted that climatological studies on hail are demanding due to the rather sparse measurement networks on the one hand and the local and short-term characteristics of hail events on the other hand. ...
... Kunz and Puskeiler (2010) combined radar-based hail detection with a cell tracking algorithm and insurance data for the German federal state of Baden-Wuerttemberg. Martius et al. (2015) give an overview about the current hail research in Europe. ...
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Overview of ESSL's severe convective storms research using the European Severe Weather Database ESWD.-Atmos
• N Dotzek
• P Groenemeijer
• D Feuerstein
• A M Holzer
Dotzek, N., P. Groenemeijer, D. Feuerstein, A.M. Holzer, 2009: Overview of ESSL's severe convective storms research using the European Severe Weather Database ESWD.-Atmos. Res 93, 575-586, DOI:10.1016/j.atmosres.2008.10.020