Spring‐summer droughts in the Czech Land in 1805–2012 and their forcings

ABSTRACT Drought is an extreme meteorological phenomenon involving serious economic consequences. In the Czech Lands, it is reflected in significant reductions in agricultural productivity, lack of water for hygiene and industry, and impacts of forest management. Mean monthly temperature and precipitation series created for the Czech Lands for 1805–2012 were used to calculate spring (MAM) and summer (JJA) drought indices (SPI‐1, SPI‐12, SPEI‐1, SPEI‐12, Z‐index and PDSI), which were then used for further analyses. Fluctuations in drought indices demonstrate an increasing long‐term dryness in the Czech climate, statistically significant for SPEI‐12 and PDSI in MAM and JJA (in MAM as well for SPEI‐1 and Z‐index). A significant concentration of drought episodes before 1880 may be attributed to a lack of precipitation, whereas the droughts of recent decades (particularly 2004–2012) are more strongly related to high temperatures. The effects of droughts are reflected in significant reductions in winter wheat and spring barley yields in the eastern province of Moravia. Regression analysis of drought forcings discloses the importance of the North Atlantic Oscillation phase and the aggregate effect of anthropogenic forcing (driven largely by increases in CO2 concentration). Their magnitude of influence varies strongly with the type of drought index and season of the year. Other factors, such as solar irradiation and the Southern Oscillation phase make only minor contributions to drought variability. The effects of volcanic activity and the Atlantic Multidecadal Oscillation are even weaker and statistically insignificant.