Since the spring 2018, a large part of Europe has been in the midst of a record-setting drought. Using long-term observations, we demonstrate that the occurrence of the 2018-2019 (consecutive) summer drought is unprecedented in the last 250 years, and its combined impact on the growing season vegetation activities is stronger compared to the 2003 European drought. Using a suite of climate model simulation outputs, we underpin the role of anthropogenic warming on exacerbating the future risk of such a consecutive drought event. Under the highest Representative Concentration Pathway, (RCP 8.5), we notice a seven-fold increase in the occurrence of the consecutive droughts, with additional 40 (± 5) million ha of cultivated areas being affected by such droughts, during the second half of the twenty-first century. The occurrence is significantly reduced under low and medium scenarios (RCP 2.6 and RCP 4.5), suggesting that an effective mitigation strategy could aid in reducing the risk of future consecutive droughts. Human-induced climate change is evident and it poses a great concern to society, primarily due to its potential to intensify extreme events around the globe 1,2. In the past 2 decades, Europe experienced an increased frequency of droughts 3,4 with estimated loss of about EUR 100 billion 5. One such devastating event was the drought in summer 2003, which was an exceptionally warm and dry year across most of central and western Europe. Historical reconstructions since 1500 C.E. suggest that it was one of the hottest summers 6 , and the event was estimated to result in a 30% reduction in gross primary production compared to previous years between 1998-2002 3. Although, the 2003 drought event was rare and exceptional, even in a multi-centennial time window, its likelihood is expected to increase in the near future 7 , mainly due to the anthropogenic warming 8-11. In the summer of 2018, temperature anomaly broke the record again in several locations across Europe, but with distinct spatial patterns. While in summer 2003 the increase in temperature was more concentrated in central and southern Europe (Fig. 1a), summer 2018 was characterised by an anomalous increase in central and northeastern Europe (Fig. 1b). Unlike the 2003 event-where the temperature anomaly (Supplementary Fig. S1) and the ecosystem carbon and energy fluxes recovered early after the summer 12 , the extreme event of 2018 persisted to the subsequent year 2019 (Fig. 1c). For all these years, the impact was strongest in the Central European region, where the increase in temperature was accompanied by concurrent significant reduction of summer precipitation (Fig. 1d-f), which led to extreme drought conditions. The intensity and spatial extent of droughts significantly affects the plant and agricultural productivity 13,14 , underlying the severity of the drought impact in Central European region, where the focus on agriculture is strong 3,7,15-17. With the use of remote sensing data-sets 18 , we find that the concurrent increased temperature with de...

Early 21st-century droughts in Europe have been broadly regarded as exceptionally severe, substantially affecting a wide range of socio-economic sectors. These extreme events were linked mainly to increases in temperature and record-breaking heatwaves that have been influencing Europe since 2000, in combination with a lack of precipitation during the summer months. Drought propagated through all respective compartments of the hydrological cycle, involving low runoff and prolonged soil moisture deficits. What if these recent droughts are not as extreme as previously thought? Using reconstructed droughts over the last 250 years, we show that although the 2003 and 2015 droughts may be regarded as the most extreme droughts driven by precipitation deficits during the vegetation period, their spatial extent and severity at a long-term European scale are less uncommon. This conclusion is evident in our concurrent investigation of three major drought types – meteorological (precipitation), agricultural (soil moisture) and hydrological (grid-scale runoff) droughts. Additionally, unprecedented drying trends for soil moisture and corresponding increases in the frequency of agricultural droughts are also observed, reflecting the recurring periods of high temperatures. Since intense and extended meteorological droughts may reemerge in the future, our study highlights concerns regarding the impacts of such extreme events when combined with persistent decrease in European soil moisture.

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Abstract. Information on extreme precipitation for future climate is needed to assess the changes in the frequency and intensity of flooding. The primary source of information in climate change impact studies is climate model projections. However, due to the coarse resolution and biases of these models, they cannot be directly used in hydrological models. Hence, statistical downscaling is necessary to address climate change impacts at the catchment scale. This study compares eight statistical downscaling methods (SDMs) often used in climate change impact studies. Four methods are based on change factors (CFs), three are bias correction (BC) methods, and one is a perfect prognosis method. The eight methods are used to downscale precipitation output from 15 regional climate models (RCMs) from the ENSEMBLES project for 11 catchments in Europe. The overall results point to an increase in extreme precipitation in most catchments in both winter and summer. For individual catchments, the downscaled time series tend to agree on the direction of the change but differ in the magnitude. Differences between the SDMs vary between the catchments and depend on the season analysed. Similarly, general conclusions cannot be drawn regarding the differences between CFs and BC methods. The performance of the BC methods during the control period also depends on the catchment, but in most cases they represent an improvement compared to RCM outputs. Analysis of the variance in the ensemble of RCMs and SDMs indicates that at least 30% and up to approximately half of the total variance is derived from the SDMs. This study illustrates the large variability in the expected changes in extreme precipitation and highlights the need for considering an ensemble of both SDMs and climate models. Recommendations are provided for the selection of the most suitable SDMs to include in the analysis.

[1] The generalized extreme value (GEV) distribution has often been used to describe the distribution of daily maximum precipitation in observed and climate model data. The model developed in this paper allows the GEV location parameter to vary over the region, while the dispersion coefficient (the ratio of the GEV scale and location parameters) and the GEV shape parameter are assumed to be constant over the region. This corresponds with the index flood assumption in hydrology. It is further assumed that all three GEV parameters vary with time, such that the relative change in a quantile of the distribution is constant over the region. This nonstationary model is fitted to the 1-day summer and 5-day winter precipitation maxima in the Rhine basin in a simulation of the Regional Atmospheric Climate Model (RACMO) for the period 1950-2099, and the results are compared with gridded observations. Except for an underestimation of the dispersion coefficient of the 5-day winter maxima by about 35%, the GEV parameters obtained from the observations are reasonably well reproduced by RACMO. A positive trend in the dispersion coefficient is found in the summer season, which implies that the relative increase of a quantile increases with increasing return period. In the winter season there is a positive trend in the location parameter and a negative trend in the shape parameter. For large quantiles the latter counterbalances the effect of the increase of the location parameter. It is shown that the standard errors of the parameter estimates are significantly reduced in the regional approach compared to those of the estimated parameters from individual grid box values, especially for the summer maxima.

The observed increase in the frequency of droughts and heatwaves over the Northern Hemisphere in the 21st century poses immediate socio-economic threats affecting the well-being of the people by triggering negative health effects. These adverse hydro-meteorological conditions can lead to agricultural and ecological impacts such as crop losses, poor water quality conditions in water bodies, and wildfires. The reduction of the streamflow resulting from a drought event combined with high air temperatures also creates a threat to existing infrastructure. Several authors have reported cases of reduction of the cooling capacity in power plants, the reduction of tonnage in fluvial transportation, and the drop in reservoir storage leading to drinking water shortages (Naumann

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