Dynamics of Water Fluxes and Storages in an Alpine Karst Catchment Under Current and Potential Future Climate Conditions
Total Page：16
File Type：pdf, Size：1020Kb
Hydrol. Earth Syst. Sci., 22, 3807–3823, 2018 https://doi.org/10.5194/hess-22-3807-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 3.0 License. Dynamics of water fluxes and storages in an Alpine karst catchment under current and potential future climate conditions Zhao Chen1, Andreas Hartmann2,3, Thorsten Wagener3, and Nico Goldscheider1 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany 2Institute of Hydrology, Albert Ludwigs University of Freiburg, Freiburg, Germany 3Department of Civil Engineering, University of Bristol, UK Correspondence: Zhao Chen ([email protected]) Received: 11 April 2017 – Discussion started: 8 May 2017 Revised: 1 April 2018 – Accepted: 6 June 2018 – Published: 18 July 2018 Abstract. Karst aquifers are difficult to manage due to their other. (4) Impacts on the karst springs are distinct; the low- unique hydrogeological characteristics. Future climate pro- est permanent spring presents a “robust” discharge behav- jections suggest a strong change in temperature and pre- ior, while the highest overflow outlet is highly sensitive to cipitation regimes in European karst regions over the next changing climate. This analysis effectively demonstrates that decades. Alpine karst systems can be especially vulnera- the impacts on subsurface flow dynamics are regulated by ble under changing hydro-meteorological conditions since the characteristic dual flow and spatially heterogeneous dis- snowmelt in mountainous environments is an important con- tributed drainage structure of the karst aquifer. Overall, our trolling process for aquifer recharge and is highly sensitive study highlights the fast groundwater dynamics in mountain- to varying climatic conditions. Our paper presents the first ous karst catchments, which make them highly vulnerable to study to investigate potential impacts of climate change on future changing climate conditions. Additionally, this work mountainous karst systems by using a combined lumped and presents a novel holistic modeling approach, which can be distributed modeling approach with consideration of subsur- transferred to similar karst systems for studying the impact face karst drainage structures. The study site is character- of climate change on local karst water resources with consid- ized by high-permeability (karstified) limestone formations eration of their individual hydrogeological complexity and and low-permeability (non-karst) sedimentary Flysch. The hydraulic heterogeneity. 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 1 Introduction April, while subsurface water storage in the karst aquifer dominates from May to October. The climate scenario runs The Alps, called the “water tower of Europe”, form head- demonstrate that varied climate conditions significantly af- waters for important regional river systems (Viviroli et al., fect the spatiotemporal distribution of water fluxes and stor- 2007). Alpine catchments are generally characterized by ages: (1) the total catchment discharge decreases under all above-average precipitation due to orographic effects, as well evaluated future climate conditions. (2) The spatiotempo- as by colder temperatures resulting in lower evapotranspira- ral discharge pattern is strongly controlled by temperature tion and temporary water storage in the form of snow and variations, which can shift the seasonal snowmelt pattern, ice (Zierl and Bugmann, 2005). Climate projections indicate with snow storage in the cold season (December to April) that a shift in snow and precipitation patterns is likely to alter decreasing significantly under all change scenarios. (3) In- catchment runoff regimes (Gobiet et al., 2014). Additionally, creased karst aquifer recharge in winter and spring, and de- extreme events, such as floods and droughts, are expected creased recharge in summer and autumn, partly offset each to increase in frequency and intensity (Dobler et al., 2013; Rössler et al., 2012). For sustainable management of water Published by Copernicus Publications on behalf of the European Geosciences Union. 3808 Z. Chen et al.: Dynamics of water fluxes and storages in an Alpine karst catchment resources in Alpine areas, it is imperative to understand the tics of flow regimes including amount, seasonality, minima complex mountainous hydrological processes (Kraller et al., and maxima, as well as impacts on other hydrological vari- 2012). ables, e.g., soil moisture and snow cover (Dobler et al., 2012; In this context, numerical models are usually applied to de- Jasper et al., 2004; Kunstmann et al., 2004; Middelkoop et scribe the hydrological processes in Alpine catchments (Ab- al., 2001; Rössler et al., 2012; Zierl and Bugmann, 2005). baspour et al., 2007; Achleitner et al., 2009; Benischke et al., Taylor et al. (2013) highlighted the impact of changing cli- 2010; Braun and Renner, 1992; Junghans et al., 2011; Kraller matic conditions on aquifer dynamics in mountainous areas. et al., 2012). Lumped models are easy to use in gauged catch- They also pointed out that the effects of receding Alpine ments because their parameters can be effectively found via glaciers on groundwater systems are poorly understood. Gre- calibration. For studying the spatial patterns of hydrologi- maud et al. (2009) and Gremaud and Goldscheider (2010) cal processes across a catchment, distributed models are re- studied a geologically complex, glacierized karst catchment quired, which discretize the model domain into a grid of in the Alps by combining tracer tests and hydrological mon- homogeneous subunits, for which surface and/or subsurface itoring and found that the changing hydro-meteorological flow can be described by flow equations derived from basic conditions affect the water storage in snow and ice signifi- physical laws. Previously, most distributed models focused cantly, which have high impact on the aquifer recharge pro- on surface hydrological variables (e.g., vegetation, soil and cesses and discharge dynamics. Finger et al. (2013) investi- snow cover) and/or anthropogenic variables (e.g., land use gated glacier meltwater runoff in a high Alpine karst catch- and water use), with relatively poor subsurface representa- ment under present and future climate conditions using tracer tions. Few studies (e.g., Kraller et al., 2012; Kunstmann et experiments, karst structure modeling and glacier melt mod- al., 2006; Kunstmann and Stadler, 2005) explicitly consid- eling. The results indicated that parts of the glacier melt- ered subsurface processes such as recharge, drainage and water are drained seasonally by the underlying karst system storage in their models for Alpine regions. It is generally ac- and the expected climate change may jeopardize the water cepted that the geological and lithological setting for moun- availability in the karst aquifer. In order to better understand tainous catchments are often complex and could have sig- climate-change effects on complex hydrological processes in nificant impact on the catchment flow regime (Goldscheider, Alpine karstic environments, we assessed the impacts of var- 2011; Rogger et al., 2013). The situation is even more com- ied climate conditions on the water fluxes and storages in plex when mountain ranges within a catchment consist of the simulated model domain, and we identified the hydro- highly permeable limestone formations hydraulically charac- logical processes most sensitive to potential climate change. terized by fissures and/or conduit drainage networks, as well For this analysis, we used a pragmatic and widely used delta as concentrated discharge via springs (Goldscheider, 2005; approach to project the climate change in the model domain Gremaud et al., 2009; Lauber and Goldscheider, 2014). (e.g., Dobler et al., 2012; Lenderink et al., 2007; Singh et al., In order to better understand complex hydrological pro- 2014). cesses in mountainous karstic catchments as well as quantify- ing their dynamics, this study presents a spatially distributed investigation of the water fluxes and storages in a high- 2 Study area elevation Alpine catchment considering its complex subsur- face heterogeneous drainage structure. The study catchment The study catchment is located in the northern Alps on the constitutes an optimal test case to explore complex hydro- Germany/Austria border (Fig. 1a). It has an area of about logical processes since it includes many typical characteris- 35 km2, and an altitude varying between 1000 m a.s.l. (the tics of Alpine catchments, such as a seasonal snow cover, lowest part of the Schwarzwasser valley) and 2230 m a.s.l. a large range of elevations and a highly varied catchment (the summit of Hochifen). The climate in the area is cool- flow regime. Furthermore, the hydrogeology in the inves- temperate and humid. The nearest permanent weather sta- tigated catchment is complex. It is characterized by high- tion lies to the east in the Breitach valley at an altitude of permeability limestone formations (karst areas) and low- 1140 m a.s.l. There, the mean monthly temperature ranges permeability Flysch sedimentary rocks (non-karst areas) as from −2.2 ◦C in January to 14.4 ◦C in July, with an annual described by Goldscheider (2005). Here, we expanded an average of 5.7 ◦C (based on data from 1961 to 1990, avail- existing model (Chen and Goldscheider, 2014) by adding a able