European climate in 2016
Climate Indicator Bulletins (CIBs) are user-driven climate information products which provide simple, effective and timely knowledge abstractions from the large amount of observation and reanalyses data available in UERRA. The bulletins focus on user groups in sectors such as disaster prevention, health, energy, water resources, ecosystems, forestry, agriculture, transport, tourism and biodiversity at European, national and local levels.
This bulletin presents an overview of the European climate in 2016 based on a large number of measurements.
Last update: 16 November 2016.
Annual mean air temperature
As described in a provisional report by the WMO,global annual mean air temperature likely reached its highest level in 2016, since the start of the global air temperature records in the late nineteenth century. First estimates suggest that global annual mean air temperature anomaly (with respect to the 1981-2010 climatology) reached 1.2°C above pre-industrial era, breaking the 1°C level for the first time. The causes behind this first-highest record anomaly can be mainly associated with the combination of the very powerful El Niño event in 2015-2016 along with the global warming trend hypothetically linked to the current new records of carbon dioxide concentrations in the atmosphere (>400 ppm -parts per million-)
The annual mean air temperature anomaly across Europe for 2016, however, was not record-breaking but it is just outside the top 5 of warmest years in the series, which stretches back to the 1950s (Fig. 1). With a temperature of 0.58°C above the long-term average and at an absolute value of 10.89°C, it ranks 6. The 2016 European annual mean air temperature anomaly contrasts with 2014 and 2015 which were two consecutive years with a record-breaking air temperature anomalies.
Fig. 1: Annual (Jan-Dec) mean air temperature anomalies averaged across Europe, with respect to the 1981-2010 climatology (central figure). Temperatures below and above normal are in blue and red, respectively, with the 2016 value in green. The spatial distribution of the sign and magnitude of monthly mean air temperature anomalies (with respect to the 1981-2010 climatology) are shown on top (Jan-Jun) and bottom (Jul-Dec) The colour scale runs from -6.5°C (dark blue) to 6.5°C (dark red)
Near-surface air temperatures are measured at a widespread network of stations in Europe. These measurements are collected and aggregated into a European air temperature database. The annual mean values in this E-OBS dataset are presented in Fig. 1 for the land area bounded between 35°-75°N and 25°W-45°E, where the December 2016 temperature is compiled from measurements (up to the 15th) and the ECMWF forecast. The green bar represents data for 2016.
The grey bars in the panel indicate the estimated uncertainties which take into account the errors introduced by spatial interpolation over areas without observing stations, and inhomogeneities in the air temperature data that mainly result from (i) station relocations, (ii) instrumentation malfunctions, (iii) instrumentation changes, (iv) different sampling intervals, and (v) observing environment changes (e.g., urbanisation), as documented in Van der Schrier et al., 2013 and Chrysanthou et al., 2014. The uncertainties tell us that although we are not 100% certain about the ranking of individual years, the overall positive trend is very pronounced since the 1980s.
During 2016, mean air temperature in January and February stand out (Fig. 2). Firstly, much cooler air temperatures than normal were experienced across eastern Europe during January (see Fig. 1, top panel). This resulted from a prevalence of easterly winds across the region throughout the month, which brought average temperature conditions of around 5°C lower than normal. Secondly, prevailing winds shifted to a southerly direction across eastern Europe in February, which led to significantly warmer conditions than normal, with a mean air temperature being up to 5°C warmer than average for the region. Both Figures 1 and 2 also display a dominance of daily mean air temperatures anomalies averaged across Europe warmer than normal until September, whereas since then periods of air temperatures colder than average have prevailed across the region.
Fig. 2: Daily mean air temperature averaged over Europe, along with the long-term mean of 1981-2010. Temperatures below and above normal are in blue and red, respectively.
Fig.3 shows the spatial distribution of the annual mean air temperature anomalies for 2016 with respect to the 1981-2010 long-term average, denoting that most of Europe was warmer than average in 2016, being the strongest warming more evident in the eastern part of Europe, with air temperatures reaching to 2.5°C above the long-term average value.
Fig. 3: Annual mean air temperature anomalies across Europe for 2016, with respect to the 1981-2010 climatology.
Exceptional air temperature events in 2016
Although the air temperature averaged over the whole Europe will not break any records in 2016, there were three extreme events which were exceptional and occurred over large areas across Europe. Maps shown below for each episode reveal the large contrasts between warm and cold conditions within the territory.
Warm nights and warm day-times
The daily minimum air temperature has seen some records in 2016. On average daily minimum air temperatures are recorded in the early hours of the morning, and may be taken to represent nighttime conditions. Especially in the month of June, nighttime air temperatures have been at an all-time high, with the highest June nighttime air temperature up to 5°C higher than the long-term average in southern Sweden, northern Germany, the Netherlands and along the Adriatic coast in Croatia. Fig. 7 shows the ranking of average nighttime air temperatures for June 2016, indicating that a large area in western Europe stretching out over the Balkan peninsula into the Middle East have seen record-breaking nighttime air temperatures in June 2016.
Fig. 7: Ranking of averaged minimum air temperature in June 2016 (1 means that June nights have been the warmest since 1950, 2 means June nights second warmest since 1950, etc.).
Over the course of the last decades, the trend in the number of warm nights across Europe has been markedly different from the trend in the number of warm day-times (the latter related to the daily maximum air temperature which is usually reached in mid-afternoon). Fig. 8 shows the difference in trends for the number of warm nights and the number of warm day-times over the 1979-2015 period for summer. Stations with positive values are those where the rise in the number of warm nights has been steeper than the rise in the number of warm day-times. Fig. 8 shows that in Spain, France, the UK, the Low Countries and southern Scandinavia, the number of warm nights in summer have been rising faster than the number of warm day-times since 1979. In the Balkan Peninsula, the reverse seems to be the case. The high June nighttime air temperatures observed over western Europe are consistent with the trend observed in the increase of the number of warm nights. There are several hypotheses why the number of warm nights increase faster than the number of warm day-times, like the Urban heat Island, but a clear view on the causes relating to the observed pattern is lacking.
Fig. 8: Difference in trends between the number of warm nights and the number of warm day-times over the 1979-2015 period for summer (June-July-August). Values are plotted if the air temperature series are qualified as homogeneous and if the trend in either the warm nights or the warm day-times is significant at the 75% level.
The annual precipitation amount over Europe for 2016 was for the Balkan peninsula, Portugal, northeastern Italy and parts of eastern Europe wetter than usual. Northwestern Europe was drier than usual in 2016 and the drought in the circum-Mediterranean, with its emphasis in the eastern Mediterranean, persists in 2016.
Fig. 9: Annual precipitation sum for 2016 as a fraction of the 1981-2010 long-term mean.
The Severe Flood Event in May/June 2016
During the course of the period 26th May to 4th June, large amounts of rain fell over southeastern/central France, Belgium, the southern part of the Netherlands and southern Germany in connection with a slow moving low pressure system (Fig. 10 left panel). The characteristic shape of this pressure pattern is particularly clear when averaged over 29-31 May 2016 (Fig. 10, right panel). It shows a low pressure system over Germany transporting moist and unstable air from eastern and southeastern Europe westward. Across northeastern France these severe showers followed a wet spring season, causing severe flooding in many river basins in the region. Notably, the river Seine in Paris peaked on 3rd June at a height greater than 6m - a height not seen since 1982. In South Germany, flash flooding also occurred during this event and was particularly severe in parts of Baden-Württemberg and Bavaria, where the station Hohenpeißenberg saw 52.5 mm in only one hour on 29 May 2016.
Fig. 10: Daily precipitation amounts in the period 29 May - 1 June 2016 (left panel, source: E-OBS). Precipitation maps for individual days from 1950 until 2016 can be found here. Right panel shows mean sea level pressure field averaged over the period of 29-31 May 2016. Blue (red) isobars indicate a (anti)cyclonic circulation system.
Heavy rainfall events as the one in the 29 May - 4 June period are rare across this region in the summer. Fig. 11 shows that the precipitation in this short period was for areas nearly twice the total May precipitation. Fig. 12 shows the time series for the maximum one-day precipitation amount in summer of a selection of stations. The one-day precipitation amount observed in the May-June 2016 period for these stations was record breaking for two of these stations. A rapid attribution study indicated that the probability of such extreme rainfall in this season has increased by about a factor 2.3 on the Seine a factor 2.0 on the Loire since 1960 and demonstrated that the flooding across the Seine river basin could be attributed to anthropogenic climate change.
Fig. 11: Precipitation sum for 29 May - 4 June 2016 as a fraction of the long-term average May monthly precipitation.
Fig. 12: Maximum one-day precipitation sums for Summer for the stations Venlo (Nl), Breitem (B) and Orleans (F). The maximum one-day precipitation values for the 29 May - 4 June 2016 period, which is plotted as the 2016 value, are among the highest on record.
Winter NAO and extratropical cyclones
During winter 2015/2016 (DJFM) the North Atlantic Oscillation (NAO) station-based index continued in its positive phase which started in 2013/2014 (see Fig. 13). This atmospheric circulation index strongly controls climate variability across northern Europe, particularly in winter. Positive phases of NAO enhance westerly winds that bring warmer, wetter and windier conditions than normal ones; almost opposite conditions prevail under positive phases across the Mediterranean region. The most noteworthy feature of the winter 2015/2016 NAO index is the extreme positive value reached in December 2015 (4.22), which represents the highest positive NAO index recorded in this month during the almost 200-year records (since 1823). This highest positive NAO phase led to the occurrence of strong low-level wind gusts associated with the development of deep extratropical cyclones, which produced large amount of rainfall in some north European countries (e.g., United Kingdom and Ireland) causing flooding. For instance, windstorms Desmond (3rd-8th December), Eva (22nd-25th December) and Frank (28th-31st December) with daily peak wind gusts up to 140 km/h are good examples of the strong westerly winds linked to this strong positive NAO phase. Even though the NAO phase were not so strongly positive in January, February and March, other very powerful windstorms crossed north Europe as Gertrude (29th January; 169 km/h) or Katie (28th March; 171 km/h), among others.
Fig. 13. Winter NAO index (December to March average) calculated as the difference between the normalized sea level pressure over Gibraltar and South Iceland according to Jones et al. (1997). Source: Climatic Research Unit.
Haylock, M.R., N. Hofstra, A.M.G. Klein Tank, E.J. Klok, P.D. Jones, M. New. 2008: A European daily high-resolution gridded dataset of surface temperature and precipitation. J. Geophys. Res., 113, D20119, doi:10.1029/2008JD10201
Authors: Richard Cornes, Christiana Photiadou, Antonello Squintu, Else van den Besselaar, Gerard van der Schrier, Igor Stepanov, Cesar Azorin-Molina, Gé Verver (KNMI, The Netherlands).
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