Karst regions offer a variety of natural resources such as freshwater and biodiversity, and many cultural resources. The World Karst Aquifer Map (WOKAM) is the first detailed and complete global geodatabase concerning the distribution of karstifiable rocks (carbonates and evaporites) representing potential karst aquifers. This study presents a statistical evaluation of WOKAM, focusing entirely on karst in carbonate rocks and addressing four main aspects: (1) global occurrence and geographic distribution of karst; (2) karst in various topographic settings and coastal areas; (3) karst in different climatic zones; and (4) populations living on karst. According to the analysis, 15.2% of the global ice-free continental surface is characterized by the presence of karstifiable carbonate rock. The largest percentage is in Europe (21.8%); the largest absolute area occurs in Asia (8.35 million km2). Globally, 31.1% of all surface exposures of carbonate rocks occur in plains, 28.1% in hills and 40.8% in mountains, and 151,400 km or 15.7% of marine coastlines are characterized by carbonate rocks. About 34.2% of all carbonate rocks occur in arid climates, followed by 28.2% in cold and 15.9% in temperate climates, whereas only 13.1 and 8.6% occur in tropical and polar climates, respectively. Globally, 1.18 billion people (16.5% of the global population) live on karst. The highest absolute number occurs in Asia (661.7 million), whereas the highest percentages are in Europe (25.3%) and North America (23.5%). These results demonstrate the global importance of karst and serve as a basis for further research and international water management strategies.

Izvleček Nataša Ravbar & Nico Goldscheider: Predlog metodologije kartiranja ranljivosti in tveganja za onesnaženje voda za va rovanje kraških vodonosnikov v SlovenijiUpoštevajoč posebnosti slovenskega krasa smo na podlagi smernic evropskega projekta COST Action 620 predlagali splošen pristop k ocenjevanju ranljivosti in tveganja kraški� voda za onesnaženje. Tako imenovani Slovenski pristop ustreza slovenski okoljski zakonodaji in omogoča primerjavo z razmerami v Evropi. Metoda pri ocenjevanju ranljivosti podtalnice upošteva časovno �idrološko spremenljivost, ponuja možnost povezovanja zaščite površinski� in podzemni� voda ter predlaga nove smernice za zaščito podzemne vode in vodni� virov, za kar je bil razvit nov faktor K (pretakanje kraški� voda v zasičeni coni). Slovenski pristop predvideva obširno analizo tveganja, ki temelji na oceni naravne ranljivosti, dejanski� in potencialni� obremenjevalcev ter pomembnosti vodnega vira oziroma podzemne vode. Predlagana metodologija je bila prvič uporabljena v zaledju vodnega vira Podstenjšek v jugoza�odni Sloveniji, rezultati pa preverjeni s pomočjo dve� sledilni� poizkusov, ki sta skupno zajemala šest injicirni� točk. Rezultati kart naravne ranljivosti, obremenjevalcev in tveganja so zadovoljivi. Preverjanje potrjuje ocenjeno naravno ranljivost reprezentativni� točk, izbrani� za injiciranje sledila. Končne karte omogočajo izpopolnjeno razmejitev vodovarstveni� pasov ter označujejo območja neustreznega ravnanja, nudijo podlago za reorganizacijo dejavnosti in za boljše rešitve v pri�od-njem načrtovanju. Ključne besede: Slovenski pristop, ranljivost podzemne vode, tveganje za onesnaženje, kraški vodonosnik, zaščita in upravljanje z vodnimi viri, preverjanje kart ranljivosti.1 Karst Researc� Institute SRC SASA, Titov trg 2, SI-6230 Postojna, Slovenia, e-mail: natasa.ravbar@zrc-sazu.si 2 Centre of Hydrogeology, University of Neuc�âtel, 2009 Neuc�âtel, Switzerland, e-mail: nico.goldsc�eider@unine.c� Abstract Nataša Ravbar & Nico Goldscheider: Proposed methodology of vulnerability and contamination risk mapping for the pro tection of karst aquifers in SloveniaOn t�e basis of work accomplis�ed by t�e European COST Action 620, a compre�ensive approac� to groundwater vulnerability and contamination risk assessment is proposed, taking into account t�e special c�aracteristics of Slovene karst aquifer systems. The Slovene Approac� is consistent wit� national environmental legislation and enables comparison across European countries. The met�od integrates temporal �ydrologi-cal variability in t�e concept of groundwater vulnerability and offers a new possibility to combine surface and groundwater source and resource protection, w�ic� required t�e development of a new K factor (karst groundwater flow wit�in t�e saturated zone). The risk analysis considers intrinsic vulnerability, contamination �azards and t�e importance of t�e source or resource. It �as been first applied to t�e Podstenjšek springs catc�ment in sout�western Slovenia and validated by means of two multi-tracer tests wi...

Abstract. Karst aquifers are difficult to manage due to their unique hydrogeological characteristics. Future climate projections suggest a strong change in temperature and precipitation regimes in European karst regions over the next decades. Alpine karst systems can be especially vulnerable under changing hydro-meteorological conditions since snowmelt in mountainous environments is an important controlling process for aquifer recharge and is highly sensitive to varying climatic conditions. Our paper presents the first study to investigate potential impacts of climate change on mountainous karst systems by using a combined lumped and distributed modeling approach with consideration of subsurface karst drainage structures. The study site is characterized by high-permeability (karstified) limestone formations and low-permeability (non-karst) sedimentary Flysch. The model simulation under current conditions demonstrates that a large proportion of precipitation infiltrates into the karst aquifer as autogenic recharge. Moreover, the result shows that surface snow storage is dominant from November to April, while subsurface water storage in the karst aquifer dominates from May to October. The climate scenario runs demonstrate that varied climate conditions significantly affect the spatiotemporal distribution of water fluxes and storages: (1) the total catchment discharge decreases under all evaluated future climate conditions. (2) The spatiotemporal discharge pattern is strongly controlled by temperature variations, which can shift the seasonal snowmelt pattern, with snow storage in the cold season (December to April) decreasing significantly under all change scenarios. (3) Increased karst aquifer recharge in winter and spring, and decreased recharge in summer and autumn, partly offset each other. (4) Impacts on the karst springs are distinct; the lowest permanent spring presents a “robust” discharge behavior, while the highest overflow outlet is highly sensitive to changing climate. This analysis effectively demonstrates that the impacts on subsurface flow dynamics are regulated by the characteristic dual flow and spatially heterogeneous distributed drainage structure of the karst aquifer. Overall, our study highlights the fast groundwater dynamics in mountainous karst catchments, which make them highly vulnerable to future changing climate conditions. Additionally, this work presents a novel holistic modeling approach, which can be transferred to similar karst systems for studying the impact of climate change on local karst water resources with consideration of their individual hydrogeological complexity and hydraulic heterogeneity.

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Karst aquifers provide drinking water for 10% of the world's population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset's coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations. Background & Summary Karst aquifers are essential sources of drinking water to about 10% of the world's population 1. In many regions across the globe, karst groundwater is also an indispensable resource for ecosystems, agriculture and, economic activities, as well as for tourism and recreation 2,3. For example, in Europe, 21.6% of the land surface is underlain by carbonate rock 4 which contributes up to 50% of supplied drinking water in some countries 5-7. However, groundwater flow in karst aquifers is characterised by a complex interplay of fast-flowing conduit and slow-flowing matrix systems 8,9. Hence, the storage capacity of karst aquifers is variable and systems are extremely vulnerable to climatic pressures, human impacts and contamination 10. In order to ensure adequate protection of karst water sources, in-depth hydrogeological knowledge is necessary. Large-scale modelling and comparative water resource research have shown the great value of large datasets in hydrology 11. Numerous studies have applied these large datasets for several purposes such as model evaluation, global parameter estimations, impact studies, statistical and comparative analyses. For instance, large-scale hydrological models such as WaterGAP 12 used discharge data from the Global Runoff Data Centre (https://www. bafg.de/GRDC) for parameter estimation. Likewise, streamflow data from the Model Parameter Estimation Experiment (MOPEX) 13 and the Global Runoff Data Centre (GDRC) were combined to derive global base flow indexes and recession constants 14. Streamflow observations of near-natural catchments obtained from UNESCO's European Water Archive (EWA) were used to investigate the streamflow trends across Europe and differentiated the impacts from climatic variability and anthropogenic dri...

Near-natural springs provide vital ecosystem goods and services (Knight 2015;Mueller et al. 2017). For example, many farms, ranches, small towns, and several national capitals (e.g., Rome, Vienna, Beirut, Damascus) use springs for potable and agricultural water (Kresic & Stevanovic 2010). Springs also have tremendous cultural, social, and economic significance. They have played important roles throughout human evolution and history (Cuthbert & Ashley 2014). Many of them have substantial recreational value (Glazier 2014; Knight 2015) (Fig. 1a, b), and the economic value of bottled spring water is enormous (Gleick 2010). Most human cultures consider springs places of vital importance for physical and spiritual well-being (Fig. 1k). Impacts, Management, and Global Conservation StatusAlthough abundant worldwide, many springs are disappearing or are impaired by local to global anthropogenic stressors, including habitat alteration, recreational use, groundwater depletion, pollution, and climate change (Glazier 2014; Knight 2015) (Fig. 1im). At local scales, individual springs are directly impaired by flow abstraction and manipulation, road and 378

Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world’s population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from <1% to around 20 to 50% of their concentrations during infiltration. Assuming realistic application rates, our simulations show that degradable pollutants like glyphosate can exceed their permissible concentrations by 3 to 19 times when reaching the groundwater. Our results are supported by independent estimates of young water fractions at 78 carbonate rock springs over Europe and a dataset of observed glyphosate concentrations in the groundwater. They imply that in times of continuing and increasing industrial and agricultural productivity, focused recharge may result in an underestimated and widespread risk to usable groundwater volumes.