Intensification of weather extremes is currently emerging as one of the most important facets of climate change. Research frontiers are in analyzing (i) the consequences for the hydrological cycle and (ii) the effects of multi-factor scenarios on ecosystems. However, in all theoretical and experimental scenarios, challenges arise as to how precipitation regimes translate into variation in soil moisture. Here, we explore soil moisture response to  experimental changes in the precipitation regime in Central Europe over a period of 5 years, particularly focusing on the effects of recurrent extreme weather events.

Intra-annual difference in weekly precipitation sums imposed by extreme drought or heavy rainfall manipulations clearly exceeded inter-annual variation in the ambient precipitation pattern during the growing season between 2005 and 2009. However, soil moisture variability in the experimental plots did not clearly reflect any altered patterns to the  manipulated precipitation regime. Natural variation in soil moisture between years was similar to within-season differences between manipulations. Strong differences in soil moisture dynamics during the growing season can however be generated by changing the temporal distribution of rainfall events while keeping the magnitude of the precipitation sum constant.

Our findings confirm a common methodological dilemma in precipitation change experiments searching for a logical way to determine how precipitation change affects communities and ecosystems on relatively short time scales: Alteration of weather regimes according to extreme value statistics and future scenarios or systematic alteration of soil moisture. For central Europe, our data suggest that other factors rather than the magnitude of rainfall exclusion or addition would appear to be decisive for ecosystem response to more extreme precipitation regimes. Response of soil moisture on frequency, return interval and timing of events is a promising approach for further exploration. In addition, buffer capacity of the ecosystem under study has to be taken into account.