3Institute of Geography, Masaryk University, Brno, Czech Republic /18 European Geosciences Union General Assembly 2019, Vienna, Austria, 7–12 April 2019 Role of teleconnections in establishing European drought variability patterns Jiří Mikšovský1,4, Miroslav Trnka2,4, Rudolf Brázdil3,4 , Michal Belda 1 1Department of Atmospheric Physics, Charles University, Prague, Czech Republic 2Department of Agrosystems and Bioclimatology, Mendel University, Brno, Czech Republic 3Institute of Geography, Masaryk University, Brno, Czech Republic 4Global Change Research Institute, Czech Academy of Sciences, Brno, Czech Republic jiri@miksovsky.info http://www.miksovsky.info/EGU2019.pptx

Standardized Precipitation Evapotranspiration Index (SPEI): /18 Charles University Prague Standardized Precipitation Evapotranspiration Index (SPEI): Data source, calculation and general properties Separation of components correlated with individual climate variability modes: Point-wise application of multiple linear regression SPEI responses to NAO, SO, AMO and PDO Role of temperature and precipitation in establishing the SPEI response patterns Deviations from linearity: How justified is purely linear approach? Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Standardized Precipitation Evapotranspiration Index (SPEI) /18 Charles University Prague Standardized Precipitation Evapotranspiration Index (SPEI) Index of meteorological drought defined from standardized difference between precipitation and potential evapotranspiration Positive values for wet conditions, negative for dry SPEI data here: calculated from monthly CRU TS gridded precipitation and potential evapo- transpiration series, in 0.5°x0.5° horizontal resolution, over the 1901-2016 period SPEI series for three sample locations (central Spain, south England, east Austria) 40.25°N, 5.25°W 51.75°N, 0.25°W 48.25°N, 16.25°E Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

/18 Charles University Prague Analysis setup Multiple linear regression between local values of SPEI, temperature or precipitation and a set of five explanatory variables; standardized regression coefficients shown Monthly data, division into cold (October-March) and warm (April-September) half-year Statistical significance evaluated by moving-block bootstrap and shown for the 95% level Explanatory variables: Linear trend North Atlantic Oscillation (NAO) index by Jones et al. (normalized pressure difference between Reykjavik and Gibraltar) Atlantic Multidecadal Oscillation (AMO) index from NOAA ESRL (detrended mean sea surface temperature (Kaplan SST v2) in northern Atlantic) Southern Oscillation (SO) index by Ropelewski & Jones (normalized pressure difference between Darwin (Australia) and Tahiti) Pacific Decadal Oscillation (PDO) index from JISAO (detrended first principal component of sea surface temperature in northern Pacific) Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Imprints of variability modes in SPEI: North Atlantic Oscillation /18 Charles University Prague Imprints of variability modes in SPEI: North Atlantic Oscillation Distinct multipolar structure, shifting between cold and warm season SPEI responses less prominent in transitory zones, making NAO less influential in some regions, e.g. near southern Baltic Sea Regression coefficients between SPEI and NAO October-March Regression coefficients between SPEI and NAO April-September Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: NAO-related responses, October to March Temperature vs. NAO Effect of precipitation boosted by temperature in most of central and southern Europe, but weakened in the north and north-west Local combination of responses Precipitation vs. NAO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: NAO-related responses, April to September Temperature vs. NAO Effect of precipitation boosted by temperature in most of Europe, except in much of Scandinavia, Scotland and Ireland Local combination of responses Precipitation vs. NAO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Imprints of variability modes in SPEI: Atlantic Multidecadal Osc. /18 Charles University Prague Imprints of variability modes in SPEI: Atlantic Multidecadal Osc. During cold part of the year, scattered imprint of AMO in the Balkans and eastern Europe (more clear when just spring is considered) During warm part of the year, significant responses especially in Iberia and France Regression coefficients between SPEI and AMO October-March Regression coefficients between SPEI and AMO April-September Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: AMO-related responses, October to March Temperature vs. AMO Effect of precipitation amplified by temperature in several small regions with significant SPEI response, but weakened in the Balkans and southern Russia Local combination of responses Precipitation vs. AMO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: AMO-related responses, April to September Temperature vs. AMO Precipitation responses largely non-significant in Iberia and France, but their combination with response in temperature results in a more significant SPEI anomaly Local combination of responses Precipitation vs. AMO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Imprints of variability modes in SPEI: Southern Oscillation /18 Charles University Prague Imprints of variability modes in SPEI: Southern Oscillation Only weak and scattered responses, statistically significant mostly in eastern Europe and the adjacent parts of Asia Somewhat stronger patterns associated with SST-based NINO indices instead of SO, but collinearity with PDO increases in such configurations Regression coefficients between SPEI and SO October-March Regression coefficients between SPEI and SO April-September Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Imprints of variability modes in SPEI: Pacific Decadal Oscillation /18 Charles University Prague Imprints of variability modes in SPEI: Pacific Decadal Oscillation Cold season: Strong geographical contrast of significant responses in Scandinavia, intermittent signal in the rest of Europe Warm season: Significant signal mostly in central Balkans and southern Russia Regression coefficients between SPEI and PDO October-March Regression coefficients between SPEI and PDO April-September Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: PDO-related responses, October to March Temperature vs. PDO SPEI responses largely following the precipitation pattern, bolstered by temperature especially in Sweden and England Local combination of responses Precipitation vs. PDO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Role of temperature and precipitation: /18 Charles University Prague Role of temperature and precipitation: PDO-related responses, April to September Temperature vs. PDO Temperature-related strengthening of SPEI responses over southern Russia and central Balkans, but suppression over central France Local combination of responses Precipitation vs. PDO standardized regression coefficient Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Deviations from linearity? /18 Charles University Prague Deviations from linearity? Responses in linear regression assumed to be directly proportional to the explanatory variables - but are they really? Even simple nonlinearity-sensitive statistics reveal differences from strict linearity, although highly variable between different regions Difference of SPEI-to-NAO regression coefficients pertaining to NAO+ and NAO- phases, October-March Difference of SPEI-to-AMO regression coefficients pertaining to AMO+ and AMO- phases, October-March Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

/18 Charles University Prague Conclusions The role NAO is generally strong, but its imprint in SPEI is diminished in some locations by mutually opposite contributions from precipitation and temperature Other variability modes are less prominent overall, but project significant influences regionally, including: AMO especially in eastern Europe during the cold half-year, in south-western Europe during the warm season PDO especially in Scandinavia during the cold season, in the Balkans and southern Russia during the warm season Notable deviations from linearity can only be found in some areas and seasons, but for these regions, application of nonlinear mappings has potential to provide more realistic picture of the local effects of teleconnections and of their possible interactions Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx

Thank you for your attention Charles University Prague Thank you for your attention jiri@miksovsky.info http://www.miksovsky.info/EGU2019.pptx Mikšovský et al.: Role of teleconnections in establishing European drought variability patterns http://www.miksovsky.info/EGU2019.pptx