Although drought trends are obvious (Figures 22.1 and 22.2) and clearly attributable to anthropogenic activities, it is important to estimate potential changes in the length, frequency, and intensity of the future droughts. To evaluate the impact of climate change on the values of the selected indicators, we tested the change in the number of days with drought stress in the topsoil layer during the period from April to June. For each 500 m grid, the weather data were modified based on the expected climate change conditions for the region. To be able to assess the development of conditions during the 2021-2040 period, we modified 1981-2010 daily weather data using a delta approach and five global circulation models. These models were selected as representations of mean values (IPSL-model of Institute of Pierre Simon Laplace, France) and to best capture the variability of expected changes in precipitation and temperature (BNU-Beijing Normal University, China; MRI-Meteorological Research Institute, Japan; CNMR-National Centre for Meteorological Research, France; and HadGEM-Hadley Centre Global Environment Model, UK). The five selected GCMs represent variability of 40 circulation models available in the CMIP5 database (Taylor et al. 2012). The RCP 4.5 (representative concentration pathway) greenhouse gas concentration trajectory and a climatic sensitivity of 3.0 K were used. As Figure 22.5 illustrates, the drought risk in the near future will not remain stable, and all five GCMs (Figure 22.5b through f) show a marked increase in the number of days with drought stress in the topsoil compared to the baseline period. The area with mean occurrence of a lack of water longer than 1 month is about 11.4 percent under the baseline climate but increases to 18-27 percent, with a fairly significant area with a water shortage on average lasting 55 days or more. Such changes would mean profound increases in the overall drought hazard. In the southeast region of the Czech Republic,
Number of days with reduced soil moisture for the 1981-2015 (baseline) period and the change in comparison with the baseline estimated using five representative GCMs for the 2021-2040 period and RCP 4.5. (a) Present climatic conditions: 1981-2015 (b-f) Expected climatic conditions: 2021-2040, RCP 4.5, 5 global circulation models (GCM).
the expansion of the highest hazard area occurs in a northward direction, while in the west the expansion covers the Elbe river lowland. Both areas are presently considered the most fertile regions in the country. An additional factor of concern is the occurrence of drought spots across the entire country, with the only exception being the northeast region. The increased incidence of drought at these sites is driven primarily by a lower soil waterholding capacity. These results indicate that hazard levels are not static and are likely to change in the future. In addition, this dynamic (i.e., hazard levels in relation to climatic change) must be considered when areas most at risk are defined. What is surprising, however, is the magnitude of the predicted changes that could occur over such a short time frame in the near future. The probability of extreme drought increases considerably under predicted future climate conditions, and these changes may occur more quickly than previously anticipated. This finding is of great concern and suggests the urgency of improving drought resilience.