Joanna Wibig Dept. of Meteorology and Climatology University of Lodz

Precipitation variability in the second half of the 20thcentury: changes in seasonality and extremes. Joanna Wibig Dept. of Meteorology and Climatology University of Lodz

INSPIRATIONS: • According to TAR IPCC (Folland et. al, 2001) precipitation in land areas of the Northern Hemisphere middle latitudes has increased. This increase was estimated on 12%. • The changes in precipitation totals are connected with changes in their distribution between seasons. • There are some indications that in warmer climate extreme precipitation events can be more frequent and the share of heavy precipitation events in annual totals shoud be greater.

The aim of this presentation is to check these statements • Has the total precipitation in Europe increased or decreased significantly and where such changes occurred? • Has the seasonal distribution of precipitation changed significantly? • Have the highest daily totals increased? • Have the share of heavy precipitation events in total precipitation changed significantly? • Are these changes related to circulation variability? • Are these changes related to global or regional warming trends?

DATA: The daily precipitation data in the period 1951-2000, mainly from the ECAD (European Climate Assessment Dataset) Klein Tank, A.M.G., et al., 2002. Daily dataset of 20th-century surface air temperature and precipitation series for the European Climate Assessment. Int. J. Climatol., 22: 1441-1453. Polish records: Lodz, Szczecin, Suwalki, Wroclaw, Przemysl (Institute of Meteorology and Water Management)

Data localization

Temperature indices: • Global temperature anomalies (monthly and annual data) • Northern Hemisphere temperature anomalies (monthly and annual data • 30-60N band temperature anomalies (monthly data) Climate Research Unit Jones, P.D. and Moberg, A., 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001. J. Climate 16, 206-223. KNMI Climate Explorer Vinnikov global temperature monthly index (RusData-TMZ_global).htm K.M.Lugina, 1999: Some features of zonal changes in the surface air temperatures under the global warming.Bulletin of St. Petersburg University, series 7, Geology and Geography, vol. 4, No 28.St. Petersburg. [in Russian]

Circulation index: Index of the NAO based on the difference of normalized sea level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur/Reykjavik, Iceland calculated on the base on three-monthly data (the interesting one and two earlier).The NAO Index Data were provided by the Climate Analysis Section, NCAR, Boulder, USA, Hurrell J W, 1995: Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation,Science:269: 676-679.

Mann – Kendall test where

Under the null hypothesis of randomness the S has a normal distribution with the mean value μs and variance σs2 given by:

Spearman rank-order correlation coefficient Ri, Si – rank series of analysed series

CHANGES in PRECIPITATION TOTALS expressed in Mann-Kendall test values - values greater (lower) than 1.66 (-1.66) mean statisticaly significant increase (decrease)

WINTER

SPRING

SUMMER

AUTUMN

Indices of seasonality: Amplitude R max – the greatest monthly total R min – the lowest monthly total

Quotient of winter to summer precipitation Quotient of autumn to spring precipitation R DJF, R MAM, R JJA, R SON – winter, spring, summer and autumn total precipitation, respectively

expressed in Mann-Kendall test values - values greater (lower) than 1.66 (-1.66) mean statisticaly significant increase (decrease)

Rank correlation coefficients between annual precipitation totals and mean temperature of the zone 30-60 NH, all NH and global, respectively

Regions of significant relations between annual precipitation totals and mean temperature of the zone 30-60 NH, all NH and global, respectively

The greatest one-day precipitation related to NH temperature anomalies

The share of 10 daily extremes in annual total in relation to NH temperature anomalies

CONCLUSIONS: The annual precipitation totals have a tendency to an increase in in the north of Europe and a decrease at the south, but these changes are statistically significant over the very small area of continent only. Within seasons: the annual pattern is present on winter maps (DJFM). Tendency to drying in summer (generally nonsignificant but with warming tendency can be related to significant water deficit). In autumn tendency to wetter climate has appeared whereas during spring slight dryness can be observed (April and May). There is a tendency to seasonal redistribution of precipitation during the year. The proportion of winter to summer precipitation inceases in the north and decreases at the south. The opposite is true when the proportion of autumn to spring precipitation is considered.

The idea that the greater proportion of precipitation falls in heavy precipitation events is not confirmed in Europe. There is an evident tendency that in warmer climate more precipitation will fall in the north and less in the south of Europe. This pattern is present also in winter and spring. During winter the NAO is related to above normal precipitation in the central and northern part of Europe and below normal at the south. In summer and autumn the dry conditions dominate over southern and central Europe and only over the north it is a tendency to wetter conditions.

The work was supported by the Polish Ministry of Education and Sciences Under Grant PBZ-KBN-086/P04/2003

Joanna Wibig Dept. of Meteorology and Climatology University of Lodz