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The water cycle in Czechia has been observed to be changing in recent years, with precipitation and evapotranspiration rates exhibiting a trend of acceleration. However, the spatial patterns of such changes remain poorly understood due to the heterogeneous network of ground observations. This study relied on multiple state-of-the-art reanalyses and hydrological modeling. Herein, we propose a novel method for benchmarking hydroclimatic data fusion based on water cycle budget closure. We ranked water cycle budget closure of 96 different combinations for precipitation, evapotranspiration, and runoff using CRU TS v4.06, E-OBS, ERA5-Land, mHM, NCEP/NCAR R1, PREC/L, and TerraClimate. Then, we used the best-ranked data to describe changes in the water cycle in Czechia over the last 60 years. We determined that Czechia is undergoing water cycle acceleration, evinced by increased atmospheric water fluxes. However, the increase in annual total precipitation is not as pronounced nor as consistent as evapotranspiration, resulting in an overall decrease in the runoff. Furthermore, non-parametric bootstrapping revealed that only evapotranspiration changes are statistically significant at the annual scale. At higher frequencies, we identified significant spatial heterogeneity when assessing the water cycle budget at a seasonal scale. Interestingly, the most significant temporal changes in Czechia occur during spring, while the spatial pattern of the change in median values stems from summer changes in the water cycle, which are the seasons within the months with statistically significant changes.

The fast depletion of soil moisture in the top soil layers characterizes flash drought events. Due to their rapid onset and intensification, flash droughts severely impact ecosystem productivity. Thus understanding their initialization mechanisms is essential for improving the skill of drought forecasting systems. Here, we examine the role of antecedent meteorological conditions that lead to flash droughts across Europe over the last 70 years (1950--2020) using ERA5 dataset. We find two major flash-drought types based on a sequence of development of antecedent hydro-meteorological conditions. The first type is characterized by a joint occurrence of two mechanisms, a decline of precipitation in conjunction with an increase of the evaporative demand, both occurring before the onset of a flash drought event. The second type, on the contrary, is characterized by high precipitation preceding the event's start, followed by a sudden precipitation deficit combined with an increase in evaporative demand at the onset of the drought. Both drought types showed increased occurrence and higher spatial coverage over the last 70 years; the second drought type has increased at a much faster rate compared to the first one specifically, over Central Europe and the Mediterranean region. Overall our study highlights the differences between the two types of flash droughts, related to varying antecedent meteorological conditions, and their changes under recent climate warming.

Study region The Morava River basin, Czech Republic, Danube Basin, Central Europe. Study focus Hydrological summer extremes represent a prominent natural hazard in Central Europe. River low flows constrain transport and water supply for agriculture, industry and society, and flood events are known to cause material damage and human loss. However, understanding changes in the frequency and magnitude of hydrological extremes is associated with great uncertainty due to the limited number of gauge observations. Here, we compile a tree-ring network to reconstruct the July–September baseflow variability of the Morava River from 1745 to 2018 CE. An ensemble of reconstructions was produced to assess the impact of calibration period length and trend on the long-term mean of reconstruction estimates. The final estimates represent the first baseflow reconstruction based on tree rings from the European continent. Simulated flows and historical documentation provide quantitative and qualitative validation of estimates prior to the 20th century. New hydrological insights for the region The reconstructions indicate an increased variability of warm-season flow during the past 100 years, with the most extreme high and low flows occurring after the start of instrumental observations. When analyzing the entire reconstruction, the negative trend in baseflow displayed by gauges across the basin after 1960 is not unprecedented. We conjecture that even lower flows could likely occur in the future considering that pre-instrumental trends were not primarily driven by rising temperature (and the evaporative demand) in contrast to the recent trends. &nbsp

Since the beginning of this century, Europe has been experiencing severe drought events (2003,2007, 2010, 2018 and 2019) which have had adverse impacts on various sectors, such as agriculture, forestry,water management, health and ecosystems. During the last few decades, projections of the impact of climatechange on hydroclimatic extremes have often been used for quantification of changes in the characteristics ofthese extremes. Recently, the research interest has been extended to include reconstructions of hydroclimaticconditions to provide historical context for present and future extremes. While there are available reconstructionsof temperature, precipitation, drought indicators, or the 20th century runoff for Europe, multi-century annualrunoff reconstructions are still lacking. In this study, we have used reconstructed precipitation and temperaturedata, Palmer Drought Severity Index and available observed runoff across 14 European catchments in orderto develop annual runoff reconstructions for the period 1500–2000 using two data-driven and one conceptuallumped hydrological model. The comparison to observed runoff data has shown a good match between thereconstructed and observed runoff and their characteristics, particularly deficit volumes. On the other hand,the validation of input precipitation fields revealed an underestimation of the variance across most of Europe,which is propagated into the reconstructed runoff series. The reconstructed runoff is available via Figshare,an open-source scientific data repository, under the DOI https://doi.org/10.6084/m9.figshare.15178107, (Sadafet al., 2021).

Since the beginning of this century, Europe has been experiencing severe drought events (2003, 2007, 2010, 2018 and 2019) which have had adverse impacts on various sectors, such as agriculture, forestry, water management, health and ecosystems. During the last few decades, projections of the impact of climate change on hydroclimatic extremes have often been used for quantification of changes in the characteristics of these extremes. Recently, the research interest has been extended to include reconstructions of hydroclimatic conditions to provide historical context for present and future extremes. While there are available reconstructions of temperature, precipitation, drought indicators, or the 20th century runoff for Europe, multi-century annual runoff reconstructions are still lacking. In this study, we have used reconstructed precipitation and temperature data, Palmer Drought Severity Index and available observed runoff across 14 European catchments in order to develop annual runoff reconstructions for the period 1500–2000 using two data-driven and one conceptual lumped hydrological model. The comparison to observed runoff data has shown a good match between the reconstructed and observed runoff and their characteristics, particularly deficit volumes. On the other hand, the validation of input precipitation fields revealed an underestimation of the variance across most of Europe, which is propagated into the reconstructed runoff series. The reconstructed runoff is available via Figshare, an open-source scientific data repository, under the DOI https://doi.org/10.6084/m9.figshare.15178107, (Sadaf et al., 2021).

Flash droughts are caused by a rapid depletion of soil moisture, which severely affect vegetation growth and agricultural production. Notwithstanding the growing importance of flash droughts under the warming climate, drivers of flash droughts across the Europe are not well understood. Here we estimate the changes in flash droughts characteristics across Europe using the latest release of ERA5 reanalysis for 1950--2019 period. We find a substantial increase in the frequency and spatial extent of flash droughts across Europe (with 79\% of the total area) during the growing season with at-least one fourth of domain showing two-fold increase in the recent decades. Increased occurrence of flash drought is largely attributed to frequent occurrence of warmer and drier co-occurring events, with a sharp gradient of changes being noticed in Mediterranean and Central European regions. Compound meteorological extremes causing the flash drought events across Europe are pre-dominantly driven by the recent climate warming. With unabated greenhouse gas emissions and current pace of climate warming, Europe is likely to face an increased occurrence of flash droughts, requiring prompt response for effective drought adaptation and management strategies.

During the period 2018–20, Europe experienced a series of hot and dry weather conditions with significant socioeconomic and environmental consequences. Yet, the extremity of these multi-year dry conditions is not recognized. Here, we provide a comprehensive spatio-temporal assessment of the drought hazard over Europe by benchmarking past exceptional events during the period from 1766–2020. We identified the 2018–20 drought event as a new benchmark having an unprecedented intensity that persisted for more than two years, exhibiting a mean areal coverage of 35.6% and an average duration of 12.2 months. What makes this event truly exceptional compared with past events is its near-surface air temperature anomaly reaching +2.8 K, which constitutes a further evidence that the ongoing global warming is exacerbating present drought events. Furthermore, future events based on climate model simulations (CMIP5) suggest that Europe should be prepared for events of comparable intensity as the 2018–20 event but with durations longer than any of those experienced in the last 250 years. Our study thus emphasizes the urgent need for adaption and mitigation strategies to cope with such multi-year drought events across Europe.

Drought is one of the main threats to food security and ecosystem productivity. During the past decades, Europe has experienced a series of droughts that caused substantial socioeconomic losses and environmental impacts. A key question is whether there are some similar characteristics in these droughts, especially when compared to the droughts that occurred further in the past. Answering this question is impossible with traditional single-index approaches and also short-term and often spatially inconsistent records. Here, using a multidimensional machine learning–based clustering algorithm and the hydrologic reconstruction of European drought, we determine the dominant drought types and investigate the changes in drought typology. We report a substantial increase in shorter warm-season droughts that are concurrent with an increase in potential evapotranspiration. If shifts reported here persist, then we will need new adaptive water management policies and, in the long run, we may observe considerable alterations in vegetation regimes and ecosystem functioning.

The recent dry and warm years in Europe are often assessed as extreme in terms of socio-economic and environmental losses. However, the impact of a drought is a function of its duration. This fact needs to be considered in the evaluation of a drought. In this study, we use a hydrological model to analyse the 2018 European drought, an event that significantly affected vegetation. We show that the severity of the soil moisture drought is high in Central Europe and Mediterranean, but it does not reach the levels observed in the first half of the 20th century. Nevertheless, we demonstrate that when the multi-year 2014-2018 period is considered, its soil moisture drought severity is exceptional in a 253-year period, especially for Central Europe. While single-year droughts can be sustained by ecosystems like forests, the repeated stress exposure of such multi-year droughts may have significant impacts on their functioning. This is already evident in some regions of Central Europe, e.g., in the Czech Republic, Germany, and Poland.

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.

We present a 250‐year (1766–2015) inventory of European meteorological, hydrological, and agricultural droughts derived from ensemble simulations of the mesoscale Hydrological Model (mHM). The inventory of droughts takes into account an ensemble of 100 simulations from the hydrological model, allowing for assessment of how different meteorological forcing and model parameterizations affect a drought ranking. For the most extreme droughts, the variability in the ranking of drought events is low, while for the years with moderate precipitation deficits, the variability increases. Despite the underlying uncertainties, our drought inventory shows increased recurrence of soil moisture droughts in the Mediterranean and declining spatial extent of hydrological drought in Central Europe over the last three decades.

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.

The use of water as a furnace cooling medium poses risks as a leakage may result in an immediate explosion and severe damage to the furnace structure. The ILTEC ionic liquid cooling technology developed by Mettop, Austria, eliminates almost all the negative effects of a water-cooled system and provides additional benefits. The ionic liquid IL-B2001 is non-explosive, completely decomposing into the gaseous components at temperature of 450 degrees C and above, non-corrosive, non-flammable, non-toxic has a wide operational temperature range of 50-200 degrees and high electrical conductivity. A fundamental characteristic of ILTEC is the use of a closed-circuit loop for the ionic liquid so that there is no contact between the ionic liquid and water and/or air and the ionic liquid is non-consumable. Examples of application described include tap hole cooling, electric furnace side wall cooling involving the creation of a freeze lining and cooling of off-gas systems., The use of water as a furnace cooling medium poses risks as a leakage may result in an immediate explosion and severe damage to the furnace structure. The ILTEC ionic liquid cooling technology developed by Mettop, Austria, eliminates almost all the negative effects of a water-cooled system and provides additional benefits. The ionic liquid IL-B2001 is non-explosive, completely decomposing into the gaseous components at temperature of 450 degrees C and above, non-corrosive, non-flammable, non-toxic has a wide operational temperature range of 50-200 degrees and high electrical conductivity. A fundamental characteristic of ILTEC is the use of a closed-circuit loop for the ionic liquid so that there is no contact between the ionic liquid and water and/or air and the ionic liquid is non-consumable. Examples of application described include tap hole cooling, electric furnace side wall cooling involving the creation of a freeze lining and cooling of off-gas systems.

It is the increasing demand for an economic and cost saving operation mode that requires effective cooling in order to achieve low refractory wear and good furnace lifetime, which is making cooling technology an important aspect of furnace operation. In addition, safety awareness is becoming more and more a focal point of the operating philosophy. However, the use of water, today's standard cooling medium, has major drawbacks as it can cause problems during furnace start up and operation, namely hydration problems, corrosion and explosion. Not to forget the severe personal as well as economical damage in case of a malfunctioning water cooling system. With the new patented cooling technology ILTEC it is possible to overcome the disadvantages of water by using an alternative cooling medium, namely the ionic liquid IL-B2001. The main characteristics are a negligible vapour pressure, the absence of explosion, the wide liquidus range and operating temperature from 50 to 200 degrees C, and the non-flammmable, non-corrosive and atoxic behaviour. All these properties lead to many areas of application, which can contribute to accomplishing a water-free production route for the entire metal processing industry., It is the increasing demand for an economic and cost saving operation mode that requires effective cooling in order to achieve low refractory wear and good furnace lifetime, which is making cooling technology an important aspect of furnace operation. In addition, safety awareness is becoming more and more a focal point of the operating philosophy. However, the use of water, today's standard cooling medium, has major drawbacks as it can cause problems during furnace start up and operation, namely hydration problems, corrosion and explosion. Not to forget the severe personal as well as economical damage in case of a malfunctioning water cooling system. With the new patented cooling technology ILTEC it is possible to overcome the disadvantages of water by using an alternative cooling medium, namely the ionic liquid IL-B2001. The main characteristics are a negligible vapour pressure, the absence of explosion, the wide liquidus range and operating temperature from 50 to 200 degrees C, and the non-flammmable, non-corrosive and atoxic behaviour. All these properties lead to many areas of application, which can contribute to accomplishing a water-free production route for the entire metal processing industry.