Long series of Swiss seasonal precipitation: regionalization, trends and influence of large‐scale flow

Quantifying precipitation variability and trends is difficult and merits regular reassessment. In the present study, the seasonal homogenized precipitation series in Switzerland is investigated for the period 1901–2013 in terms of trends, inter-annual variability and the influence of large-scale flow. An objective clustering is applied, resulting in 32 distinct precipitation regions. Trends are analysed for all 32 regions with moving trend windows, and statistical significance (p < 0.05) is assessed with Theil–Sen trend estimates and nonparametric Mann–Kendall trend tests. Inter-annual precipitation varies considerably regionally and seasonally. Of 2720 analysed trend windows of 33–113 years in length, 194 (7.1%) show a significantly positive trend and 10 (0.4%) a significantly negative trend. Most of the significantly positive trends are found for 50+ year series for winter, autumn and the year. 81% of the annual and 72% of the winter series show positive trends (0–3% per decade) for the 1901–2013 period. The trends are significant for 34% (22%) of the annual (winter) series. Long-term trends are generally in line with earlier estimates in literature considering somewhat shorter time periods. Significantly negative trends are only found for winter in the most recent decades. No significant trends are found for inter-annual variability and changes in the 10th and 90th percentile seasonal extreme precipitation thresholds. The influence of large-scale flow on precipitation variability is strongest in winter. The leading pattern for northern Switzerland (nS) is the Euro-Atlantic blocking pattern. For southern Switzerland (sS), the Eastern Atlantic (Scandinavian) pattern is dominant in winter (autumn). In nS, wet (dry) seasons are linked to south-westerly (north-easterly) flow. In sS, wet (dry) seasons are linked to southerly (northerly) flow. Strong evidence for imprints of atmospheric blocking on seasonal precipitation variability is found in winter and autumn. In spring, a high pressure anomaly stretching from the mid-Atlantic to central Europe is indicative of dryness in nS.

[1]  Dimitrios Gyalistras,et al.  North Atlantic Oscillation – Concepts And Studies , 2001 .

[2]  M. Kendall,et al.  Rank Correlation Methods , 1949 .

[3]  H. B. Mann.  Nonparametric Tests Against Trend , 1945 .

[4]  Daniel F. Rex,et al.  Blocking Action in the Middle Troposphere and its Effect upon Regional Climate II. The Climatology of Blocking Action , 1950 .

[5]  Martin Beniston,et al.  An analysis of regional climate change in Switzerland , 1994 .

[6]  Harald Lejenäs,et al.  Characteristics of northern hemisphere blocking as determined from a long time series of observational data , 1983 .

[7]  C. Appenzeller,et al.  Swiss alpine snow pack variability: Major patterns and links to local climate and large-scale flow , 2006 .

[8]  J. Hurrell.  Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation , 1995, Science.

[9]  P. Sen.  Estimates of the Regression Coefficient Based on Kendall's Tau , 1968 .

[10]  Michele Brunetti,et al.  Changes in total precipitation, rainy days and extreme events in northeastern Italy , 2001 .

[11]  A. Barnston,et al.  Classification, seasonality and persistence of low-frequency atmospheric circulation patterns , 1987 .

[12]  Arthur T. DeGaetano,et al.  Spatial grouping of United States climate stations using a hybrid clustering approach , 2001 .

[13]  F. James Rohlf,et al.  Biometry: The Principles and Practice of Statistics in Biological Research , 1969 .

[14]  A. Møller,et al.  Immunocompetence, ornamentation, and viability of male barn swallows (Hirundo rustica). , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[15]  P. Jones,et al.  The Twentieth Century Reanalysis Project , 2009 .

[16]  V. Ivanov,et al.  Investigating Interannual Variability of Precipitation at the Global Scale: Is There a Connection with Seasonality? , 2012 .

[17]  C. Frei,et al.  Trends of heavy precipitation and wet and dry spells in Switzerland during the 20th century , 2005 .

[18]  C. Schär,et al.  Detection Probability of Trends in Rare Events: Theory and Application to Heavy Precipitation in the Alpine Region , 2001 .

[19]  R. Stolarski,et al.  Climate Variability and Extremes during the Past 100 Years , 2008 .

[20]  C. Frei,et al.  Long‐term variations and trends of mesoscale precipitation in the Alps: recalculation and update for 1901–2008 , 2016 .

[21]  W. Briggs.  Statistical Methods in the Atmospheric Sciences , 2007 .

[22]  Rob J Hyndman,et al.  Sample Quantiles in Statistical Packages , 1996 .

[23]  C. Frei,et al.  The climate of daily precipitation in the Alps: development and analysis of a high‐resolution grid dataset from pan‐Alpine rain‐gauge data , 2014 .

[24]  C. Schär,et al.  A PRECIPITATION CLIMATOLOGY OF THE ALPS FROM HIGH-RESOLUTION RAIN-GAUGE OBSERVATIONS , 1998 .

[25]  R. Katz,et al.  Extreme events in a changing climate: Variability is more important than averages , 1992 .

[26]  Peter J. Rousseeuw,et al.  Finding Groups in Data: An Introduction to Cluster Analysis , 1990 .

[27]  R. Trigo,et al.  Climate impact of the European winter blocking episodes from the NCEP/NCAR Reanalyses , 2004 .

[28]  M. Begert,et al.  Homogeneous temperature and precipitation series of Switzerland from 1864 to 2000 , 2005 .

[29]  C. Schär,et al.  A principal component and long‐term trend analysis of daily precipitation in Switzerland , 1997 .

[30]  M. Rebetez,et al.  Regionalization of precipitation in Switzerland by means of principal component analysis , 1997 .

[31]  F. Molteni,et al.  Wintertime variability in the Euro‐Atlantic region in observations and in ECMWF seasonal ensemble experiments , 2000 .

[32]  H. Sodemann,et al.  Seasonal and inter‐annual variability of the moisture sources for Alpine precipitation during 1995–2002 , 2009 .

[33]  W. Cleveland.  Robust Locally Weighted Regression and Smoothing Scatterplots , 1979 .

[34]  H. Theil.  A Rank-Invariant Method of Linear and Polynomial Regression Analysis , 1992 .

[35]  C. Schär,et al.  Mesoscale precipitation variability in the region of the European Alps during the 20th century , 2002 .