D4 Julkaistu kehittämis- tai tutkimusraportti tai -selvitys
Occurrence of meteorological summer dry spells and dry days in northern Europe during the 20th century
Tekijät: Hohenthal Johanna, Venäläinen Ari, Ylhäisi Jussi, Jylhä Kirsti, Käyhkö Jukka
Kustantaja: Ilmatieteen laitos
Julkaisuvuosi: 2014
Journal: Raportteja - ilmatieteen laitos
Vuosikerta: 2014
Numero: 1
ISBN: 978-951-697-807-2
eISBN: 978-951-697-808-9
eISSN: 0782-6079
Verkko-osoite: https://helda.helsinki.fi/handle/10138/44694
Tiivistelmä
Abstract
In spite of the relatively humid climate of Northern Europe, prolonged meteorological dry
spells do occasionally cause problems for the water supply in different sectors of society.
During recent decades, total annual precipitation has increased in the region, especially
during winter. A linear change in total precipitation does not necessarily indicate a change in
the occurrence of meteorological drought across different time scales. In this study,
temporal changes of meteorological summer (May-August) dry spells (MDS) and dry days
(MDD) are analysed using measured precipitation observations from 12 weather stations
located around Northern Europe. The statistics studied are the number of MDDs (<1.0 and
<0.1 mm) per selected periods, plus the lengths of the longest MDSs during which the total
accumulated precipitation remains under certain thresholds, namely 10 and 100 mm. The
results suggest that, in general, the lengths of the longest MDSs and the numbers of MDDs
do not differ remarkably between the stations, median value being 26/80 days (<10/<100
mm rain) and 87/70 days (<1.0/<0.1 mm/day), respectively. A distinct exception is Bergen,
in Norway, where the lengths of the longest MDSs are shorter (19 and 41 days, on average)
and the numbers of MDDs lower (ca. 64 and 50 days) than at the other stations. During the
period of homogeneous instrumental precipitation observations, the occurrence of summer
MDSs and MDD have remained the same at most of the stations. Only a few statistically
significant increasing temporal trends appear in the time series of MDDs in the southern
parts of the region. In the north, one statistically significant decreasing trend has been
detected.
In spite of the relatively humid climate of Northern Europe, prolonged meteorological dry spells do occasionally cause problems for the water supply in different sectors of society. During recent decades, total annual precipitation has increased in the region, especially during winter. A linear change in total precipitation does not necessarily indicate a change in the occurrence of meteorological drought across different time scales. In this study, temporal changes of meteorological summer (May-August) dry spells (MDS) and dry days (MDD) are analysed using measured precipitation observations from 12 weather stations located around Northern Europe. The statistics studied are the number of MDDs (<1.0 and <0.1 mm) per selected periods, plus the lengths of the longest MDSs during which the total accumulated precipitation remains under certain thresholds, namely 10 and 100 mm. The results suggest that, in general, the lengths of the longest MDSs and the numbers of MDDs do not differ remarkably between the stations, median value being 26/80 days (<10/<100 mm rain) and 87/70 days (<1.0/<0.1 mm/day), respectively. A distinct exception is Bergen, in Norway, where the lengths of the longest MDSs are shorter (19 and 41 days, on average) and the numbers of MDDs lower (ca. 64 and 50 days) than at the other stations. During the period of homogeneous instrumental precipitation observations, the occurrence of summer MDSs and MDD have remained the same at most of the stations. Only a few statistically significant increasing temporal trends appear in the time series of MDDs in the southern parts of the region. In the north, one statistically significant decreasing trend has been detected.
Abstract
In spite of the relatively humid climate of Northern Europe, prolonged meteorological dry
spells do occasionally cause problems for the water supply in different sectors of society.
During recent decades, total annual precipitation has increased in the region, especially
during winter. A linear change in total precipitation does not necessarily indicate a change in
the occurrence of meteorological drought across different time scales. In this study,
temporal changes of meteorological summer (May-August) dry spells (MDS) and dry days
(MDD) are analysed using measured precipitation observations from 12 weather stations
located around Northern Europe. The statistics studied are the number of MDDs (<1.0 and
<0.1 mm) per selected periods, plus the lengths of the longest MDSs during which the total
accumulated precipitation remains under certain thresholds, namely 10 and 100 mm. The
results suggest that, in general, the lengths of the longest MDSs and the numbers of MDDs
do not differ remarkably between the stations, median value being 26/80 days (<10/<100
mm rain) and 87/70 days (<1.0/<0.1 mm/day), respectively. A distinct exception is Bergen,
in Norway, where the lengths of the longest MDSs are shorter (19 and 41 days, on average)
and the numbers of MDDs lower (ca. 64 and 50 days) than at the other stations. During the
period of homogeneous instrumental precipitation observations, the occurrence of summer
MDSs and MDD have remained the same at most of the stations. Only a few statistically
significant increasing temporal trends appear in the time series of MDDs in the southern
parts of the region. In the north, one statistically significant decreasing trend has been
detected.
In spite of the relatively humid climate of Northern Europe, prolonged meteorological dry spells do occasionally cause problems for the water supply in different sectors of society. During recent decades, total annual precipitation has increased in the region, especially during winter. A linear change in total precipitation does not necessarily indicate a change in the occurrence of meteorological drought across different time scales. In this study, temporal changes of meteorological summer (May-August) dry spells (MDS) and dry days (MDD) are analysed using measured precipitation observations from 12 weather stations located around Northern Europe. The statistics studied are the number of MDDs (<1.0 and <0.1 mm) per selected periods, plus the lengths of the longest MDSs during which the total accumulated precipitation remains under certain thresholds, namely 10 and 100 mm. The results suggest that, in general, the lengths of the longest MDSs and the numbers of MDDs do not differ remarkably between the stations, median value being 26/80 days (<10/<100 mm rain) and 87/70 days (<1.0/<0.1 mm/day), respectively. A distinct exception is Bergen, in Norway, where the lengths of the longest MDSs are shorter (19 and 41 days, on average) and the numbers of MDDs lower (ca. 64 and 50 days) than at the other stations. During the period of homogeneous instrumental precipitation observations, the occurrence of summer MDSs and MDD have remained the same at most of the stations. Only a few statistically significant increasing temporal trends appear in the time series of MDDs in the southern parts of the region. In the north, one statistically significant decreasing trend has been detected.
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