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Among the variables that can be employed to characterize agricultural drought, soil drought is of particular importance. This contribution uses gridded soil-drought values calculated from the SoilClim model for the 1961-2019 period to analyse soil drought episodes (based on the 10th percentile) in four lowlands, relatively homogeneous regions in central Europe that provide a longitudinal transect over central Europe. These areas are predominantly located at altitudes of below 400 m asl and include central Bohemia, southern Moravia and an adjacent part of Slovakia, southern Slovakia and eastern Slovakia. The results indicate that, after 1990, such episodes occurred largely in the summer half-year (April-September), accompanied by an increasing linear trend in the 1961-2019 period, while the situation was reversed in the winter half-year (October-March). Selected drought episodes are further divided into three phases (Phase I - origin, Phase II - course, Phase III - end) and investigated separately in terms of precipitation and objective classification of circulation types based on flow strength, direction and vorticity. Decreases in the frequency of precipitation-rich cyclonic and the directional types associated with higher daily precipitation totals, together with increases in precipitation-poor anticyclonic types, were responsible for soil-drought Phases I and II, with the opposite pertaining to Phase III. Differences in the effects of circulation types on precipitation and soil-drought occurrence were considerable, particularly for central Bohemia compared with the other three regions. The results obtained are also discussed with respect to data uncertainty and their broader spatiotemporal context.

We assessed future changes in spring frost risk for the Aare river catchment that comprises the Swiss Plateau, the most important agricultural region of Switzerland. An ensemble of 15 bias-corrected regional climate model (RCM) simulations from the EXAR data set forced by the RCP 4.5 and RCP 8.5 concentration pathways were analysed for two future periods. Correlating actual meteorological observations and Swiss phenological spring index, we proposed and tested an RCM-compatible methodology (based on temperature data only) for estimating a start of spring and severity of frost events. In the historical climate, a significant advancement in start of spring was observed and frost events were more frequent in those years in which spring started sooner. In 2021&ndash, 2050, spring is projected to start eight (twelve) days earlier, considering the RCP 4.5 (8.5) scenario. Substantial changes were simulated for the 2070&ndash, 2099 period under RCP 8.5, when the total severity of frost events was projected to be increased by a factor of 2.1 compared to the historical climate. The study revealed the possible future increase of vegetation exposure to spring frost in Switzerland and that this phenomenon is noticeable even in the near future under the &lsquo, low concentration&rsquo, RCP 4.5 scenario.

The study examines climate change scenarios of Central European heat waves with a focus on related uncertainties in a large ensemble of regional climate model (RCM) simulations from the EURO-CORDEX and ENSEMBLES projects. Historical runs (1970–1999) driven by global climate models (GCMs) are evaluated against the E-OBS gridded data set in the first step. Although the RCMs are found to reproduce the frequency of heat waves quite well, those RCMs with the coarser grid (25 and 50 km) considerably overestimate the frequency of severe heat waves. This deficiency is improved in higher-resolution (12.5 km) EURO-CORDEX RCMs. In the near future (2020–2049), heat waves are projected to be nearly twice as frequent in comparison to the modelled historical period, and the increase is even larger for severe heat waves. Uncertainty originates mainly from the selection of RCMs and GCMs because the increase is similar for all concentration scenarios. For the late twenty-first century (2070–2099), a substantial increase in heat wave frequencies is projected, the magnitude of which depends mainly upon concentration scenario. Three to four heat waves per summer are projected in this period (compared to less than one in the recent climate), and severe heat waves are likely to become a regular phenomenon. This increment is primarily driven by a positive shift of temperature distribution, but changes in its scale and enhanced temporal autocorrelation of temperature also contribute to the projected increase in heat wave frequencies.

The aim of this study was to evaluate temperature and sea-level pressure (SLP) fields and to analyse a related anomalous flow over midlatitudes simulated by the CNRM-CM5.1 global climate model (GCM). Simulated flow over midlatitudes of the Northern Hemisphere was assessed through flow indices, classified into 11 circulation types. Reference data were taken from the NOAA-CIRES 20th Century Reanalysis, version 2c. CNRM-CM5.1 exhibited analogous temperature biases to those reported for the mean of the CMIP5 GCMs’ ensemble. The most prominent features were an erroneous temperature dipole pattern in the Atlantic Ocean and a warm bias over regions of deep water upwelling (locally exceeding 5°C). The latter feature was associated with negative SLP biases in those regions. Too low pressure was found over midlatitudes of the Northern Hemisphere, and CNRM-CM5.1 simulated too frequent zonal flow in these latitudes. The usage of three ensemble members with different initial conditions did not improve model’s outputs because the bias is found to be considerably larger compared to the ensemble members’ spread. The study showed that temperature and SLP biases are connected in certain regions, suggesting that improvement of GCMs and development of bias correction methods should be carried out with a complex insight.

Heat waves are one of the main concerns related to the impacts of climate change, because their frequency and severity are projected to increase in a future climate. The objectives of this work are to study the long-term variability of heat waves over Argentina and to estimate recurrence probability of the most severe 2008 heat wave in Buenos Aires. We used three definitions of heat waves that were based on (1) daily maximum temperature above the 90th percentile (MaxTHW), (2) daily minimum temperature above the 90th percentile (MinTHW) and (3) both maximum and minimum temperatures above the corresponding 90th percentiles (EHW). The minimum length of a heat wave was 3 days, and the analysis was performed over the October–March period. Decadal values in Buenos Aires experienced clear increases in heat waves according to MinTHW and EHW, with the highest frequency for both in the 2001–2010 decade, but at other stations, combinations of different trends and decadal variability resulted in some cases in a decrease of extreme heat waves. In the north-western part of the country, a strong positive change in the last decade was found, mainly due to the increment in the persistence of MinTHW but also accompanied by increases in MaxTHW. In general, other stations show a clear positive trend in MinTHW and decadal variability in MaxTHW, with the largest EHW cases in the last decade. We also estimated recurrence probability of the longest and most severe heat wave in Buenos Aires (over 1909–2010, according to intensity measured by the cumulative excess of maximum daily temperature above the 90th percentile) that occurred from 3 to 14 November 2008, by means of simulations with a stochastic first-order autoregressive model. The recurrence probability of such long and severe heat wave is small in the present climate but it is likely to increase substantially in the near future even under a moderate warming trend. Fil: Rusticucci, Matilde Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Kyselý, Jan. Academy of Sciences of the Czech Republic. Institute of Atmospheric Physics; República Checa. Academy of Sciences of the Czech Republic. Global Change Research Centre; República Checa Fil: Almeira, Gustavo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Lhotka, Ondřej. Academy of Sciences of the Czech Republic. Institute of Atmospheric Physics; República Checa. Academy of Sciences of the Czech Republic. Global Change Research Centre; República Checa. Charles University; República Checa