Andreas Hartmann

Technische Universität Dresden | TUD · Institute of Groundwater Management

Data scarcity in many areas around the world represents a major problem for hydrological model calibrations. Global parameter estimates and global forcing can provide possibilities to access hydrological responses in ungauged regions. In this study, we applied HBV global parameter estimates considering uncertainty in the Upper Neckar and Upper Danu...

Modelling solute mixing and transport processes is one of the key steps to effectively managing karstic groundwater resources, particularly under the threat of climate change and risk of contamination. For that reason, a considerable body of literature has been devoted to understanding and describing solute mixing and transport processes in karst a...

Understanding groundwater recharge processes is important for sustainable water resource management. Experimental approaches to study recharge in karst areas often focus on analysing the aquifer response using a disintegration of its outlet signals, but only a few approaches directly investigate the recharge processes that occur at the surface of t...

The robustness of a hydrological model is mainly dependent on how well the simulations resemble a quantity of interest, typically discharge, which is mainly achieved by successful model calibration. Performance metrics are used to quantify to what degree the system of interest is represented by a model. However, as there is not a general procedure...

Time series of hydrochemical parameters support the investigation of dominant karst hydrological processes and conceptual model structures. Nevertheless, high costs for sample collection and analyses cause hydrochemical data to be rarely available at a sufficiently high temporal resolution, e.g. hourly. The electrical conductivity (EC), however, ca...

Analysis of karst spring recession hydrographs is essential for determining hydraulic parameters, geometric characteristics, and transfer mechanisms that describe the dynamic nature of karst aquifer systems. The extraction and separation of different fast- and slow-flow components constituting a karst spring recession hydrograph typically involve m...

Karst aquifers are important sources of fresh water on a global scale. The hydrological modelling of karst spring discharge, however, still poses a challenge. In this study we apply a transfer function noise (TFN) model in combination with a bucket-type recharge model to simulate and predict karst spring discharge. The application of the noise mode...

The Kling–Gupta efficiency (KGE) is a widely used performance measure because of its advantages in orthogonally considering bias, correlation and variability. However, in most Markov chain Monte Carlo (MCMC) algorithms, error-based formal likelihood functions are commonly applied. Due to its statistically informal characteristics, using the origina...

Protected areas are a key tool for conserving biodiversity, sustaining ecosystem services and improving human well-being. Global initiatives that aim to expand and connect protected areas generally focus on controlling ‘above ground’ impacts such as land use, overlooking the potential for human actions in adjacent areas to affect protected areas th...

Quantifying the spatial variability of groundwater recharge is crucial for water resource management under changing land use conditions. Hydrological model performance is highly influenced particularly for peak discharge simulation for the wetland-dominated watersheds. This study aimed at improving the performance of a numerical model at a wetland-...

Table S1 Correlation coefficients (CC) between catchment properties and model parameters. Table S2 Catchment properties that are derived for streamflow prediction in the ungauged catchments using the 14 parameter sets obtained by the weighted regression. Table S3 The maximum NSE on the monthly scale for the best parameters derived from calibration,...

In this study to quantify the uncertainty of the regionalization procedure, we apply all 14 regionalized models that were created using the leave-one-out evaluation to the ungauged catchments. With this regard, an ensemble of 14 predicted streamflow time series is produced for each ungauged catchment to reflect the regionalization uncertainty. The...

Understanding groundwater recharge processes is important for sustainable water resource management. Experimental approaches to study recharge in karst areas often focus on analysing the aquifer response using a disintegration of its outlet signals, but only a few directly investigate the recharge processes that occur at the surface of the system....

Quantifying uncertainties in water resource prediction in data-scarce regions is essential for resource development. We use globally available datasets of precipitation and potential evapotranspiration for the regionalization of model parameters in the data-scarce regions of Ethiopia. A regional model was developed based on 14 gauged catchments. Th...

Droughts cause large economic and social impacts all over the world. During drought, groundwater maintains streamflow and can help to mitigate impacts. It governs how drought propagates through the hydrological cycle. Groundwater flows between topographic catchments may modify groundwater dynamics considerably and also influence groundwater’s droug...

Lumped parameter modeling approach has been widely applied in karst hydrology for, among other applications, groundwater availability assessment in a context of global change. Nonetheless, such approach generally does not account for land-cover land-use (LCLU) and its impacts on recharge processes. Then, considering a semi-distributed recharge cons...

The lumped parameter modeling approach has been widely applied in karst hydrology for, among other applications, the understanding of their functioning of the assessment or groundwater availability in a context of global change. Nonetheless, such an approach generally does not account for land-cover land-use (LCLU) changes and their potential impac...

The study determined rainfall onset and cessation dates, and length of rainy season (LRS) in the Oti River Basin (ORB) using historical data (1981–2010) and future (2021–2050) model data. Historical data were from meteorological stations, Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) and National Aeronautics and Space Administ...

Due to EC’s easy recordability and the existence of a strong correlation between EC (electrical conductivity) and discharge in certain catchments, EC is a potential predictor of discharge. This potential has not yet to be widely addressed. In this paper, we investigate the feasibility of using EC as a proxy for long-term discharge monitoring in a s...

Understanding rainwater dispersion in a spatiotemporal context is invaluable toward resourceful water management and a food-secure society. This study, therefore, assessed the variations in rainfall at a spatiotemporal scale in the Oti River Basin of West Africa for observed (1981–2010) and future periods (2021–2050) under the representative concen...

a.Aim This work introduces the hydrology of groundwater systems. Focusing on natural groundwater systems, this work is meant to get students of environmental, biological, or engineering sciences started with hydrogeology. b.Main concepts and methods covered The most relevant hydrogeological technical terms are introduced and defined. In separate se...

Continental- to global-scale hydrologic and land surface models increasingly include representations of the groundwater system. Such large-scale models are essential for examining, communicating, and understanding the dynamic interactions between the Earth system above and below the land surface as well as the opportunities and limits of groundwate...

The Kling-Gupta Efficiency (KGE) is a widely used performance measure because of its advantages in orthogonally considering bias, correlation and variability. However, in most Markov chain Monte Carlo (MCMC) algorithms, error-based formal likelihood functions are commonly applied. Due to its statistically informal characteristics, using the origina...

Recession Curve Analysis is a common method to characterize karstic aquifers and their discharge dynamics. Although this technique provides crucial information on quantifying system hydrodynamic properties, the manually selected recession curves analysis is neither a practical technique to cover all candidate recession curves, nor it allows extract...

Groundwater flow and transport processes in karst systems are mainly controlled by physical system characteristics. Process-related parameters of fractured rock matrix and solutionally-enlarged conduits, as well as conduit network configuration, challenging to determine and/or conceptualize, control the dynamic responses observed as hydro-chemo-the...

Though karst aquifers are important sources of drinking water on a global scale, these systems are still insuffciently understood regarding adequate model representation. Time Series Analysis (TSA), as a data‐driven approach, has been demonstrated to be useful for the characterization of karst system hydrodynamics with sparse data. Recently, transf...

Our ability to fully and reliably observe and simulate the terrestrial hydrologic cycle is limited, and in‐depth experimental studies cover only a tiny fraction of our landscape. On medieval maps, unexplored regions were shown as images of dragons—displaying a fear of the unknown. With time, cartographers dared to leave such areas blank, thus invit...

In Ethiopia more than 80 % of big freshwater lakes are located in the Rift Valley Lake Basin (RVLB), serving over 15 million people a multipurpose water supply. The basin covers an area of 53,035 km 2 , and most of the catchments recharging these lakes are ungauged and their water balance is not well quantified, hence limiting the development of ap...

In Ethiopia, more than 80% of big freshwater lakes are located in the Rift Valley Lake Basin, which is serving for multipurpose water use of over 30 million people. The basin is one of the most densely populated regions in Ethiopia and it covers an area of 53,035 km 2. However, most of the catchments recharging these lakes are ungauged and their wa...

Annually laminated speleothems have the potential to provide information on high-frequency climate variability and, simultaneously, provide good chronological constraints. However, there are distinct types of speleothem annual laminae, from physical to chemical, and a common mechanism that links their formation has yet to be found. Here, we analyze...

The complexity of karst groundwater flow modelling is reflected by the amount of simulation approaches. The goal of the Karst Modelling Challenge (KMC) is comparing different approaches on one single system using the same data set. Thirteen teams with different computational models for simulating discharge variations at karst springs have applied t...

Environmental tracers have been used to separate streamflow components for many years. They allow to quantify the contribution of water originating from different sources such as direct runoff from precipitation, subsurface stormflow or groundwater to total streamflow at variable flow conditions. Although previous studies have explored the value of...

Significance Clean groundwater is essential for water supply in many regions of the world. Fast flow to the groundwater through enlarged cracks and fissures, which is known to transmit short-lived pollutants into the groundwater, is often neglected in large-scale studies. We quantify the rapid transport of pollutants by fast flow into the carbonate...

Analysis of karst spring recession hydrographs is essential for determining hydraulic parameters, geometric characteristics and transfer mechanisms that describe the dynamic nature of karst aquifer systems. The extraction and separation of different fast and slow flow components constituting karst spring recession hydrograph typically involve manua...

A global investigation discovers where annually laminated stalagmites are found, analyzes their growth properties, and explains how they can be best used in Earth science research.

Continental- to global-scale hydrologic and land surface models increasingly include representations of the groundwater system. Such large-scale models are essential for examining, communicating, and understanding the dynamic interactions between the Earth System above and below the land surface as well as the opportunities and limits of groundwate...

Electrical conductivity (EC) of karst spring discharge has always been a fundamental variable to characterize karst systems. However, to incorporate EC into the lumped hydrologic modeling is challenging but has a huge potential since EC observations are widely collected. In this paper, we present a new framework to integrate EC into lumped karst hy...

Due to EC's easy recordability and the existence of a strong correlation between EC and discharge in certain catchments, EC is a potential predictor of discharge. This potential has yet to be widely addressed. In this paper, we investigate the feasibility of using EC as a proxy for long-term discharge monitoring in a small karst catchment where EC...

Karst hydrological models are widely used for simulating groundwater dynamics at the aquifer scale. However, modeling streamflow of a topographic catchment that is partially covered by karst is rarely reported. This absence is due to difficulties of properly considering the strong differences of karstic and nonkarstic hydrodynamics and the widespre...

Quantifying rainfall recharge thresholds, including their spatial and temporal heterogeneity, is of fundamental importance to better understand recharge processes and improving estimation of recharge rates. Caves provide a unique observatory into the percolation of water from the surface to the water table at the timescale of individual rainfall re...

The design and construction of dams are risky in karst regions with active tectonic settings and strong heterogeneity due to their leakage potential. Hydrogeological characterization by karst-specific methods can be used to reduce the risk of improper dam construction. Numerous karstic dams have been constructed in the world in simple tectonic sett...

Comprehensive management of karst water resources requires sufficient understanding of their dynamics and karst-specific modeling tools. However, the limited availability of observations of karstic groundwater dynamics has been prohibiting the assessment of karst water resources at regional to global scales. This paper presents the first global eff...

Karst hydrological models are widely used for simulating groundwater dynamics at the aquifer scale. However, modeling streamflow of a topographic catchment that is partially covered by karst is rarely reported. This is due to difficulties of properly considering the strong differences of karstic and non-karstic hydrodynamics and the widespread occu...

Excess nitrogen (N) deposition and gaseous N emissions from industrial, domestic, and agricultural sources have led to increased nitrate leaching, the loss of biological diversity, and has affected carbon (C) sequestration in forest ecosystems. Nitrate leaching affects the purity of karst water resources, which contribute around 50% to Austria’s dr...

Topographically delineated catchments are the common spatial unit to connect human activities and climate change with their consequences for water availability as a prerequisite for sustainable water management. However, inter-catchment groundwater flow and limited connectivity within the catchment results in effective catchment areas different fro...

Electrical conductivity (EC) of karst spring discharge has always been a fundamental variable to characterize karst aquifers. However, to incorporate EC into the hydrologic modeling is challenging but has a huge potential since EC observations are widely collected. In this paper, we presented a new framework to integrate EC into lumped karst hydrol...

Continental- to global-scale hydrologic and land surface models increasingly include representations of the groundwater system, driven by crucial Earth science and sustainability problems. These models are essential for examining, communicating, and understanding the dynamic interactions between the Earth System above and below the land surface as...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

In a context of climate, environmental, ecological and socio-economical changes, understanding and predicting the response of hydrological systems on regional to global spatial scales, and on infra-seasonal to multidecadal time-scales, are major topics that must be considered to tackle the challenge of water resource management sustainability. In t...

Substantial changes of climate and land use are projected in many karst regions in the world for the next decades. Despite these projections, only few studies have been performed to quantify the impact of climate change and land use change on karst water resources. This is mainly due to a lack of observations of the karstic recharge and groundwater...

Groundwater pollution threatens human and ecosystem health in many areas around the globe. Shortcuts to the groundwater through concentrated recharge are known to transmit short-lived pollutants into carbonate aquifers endangering water quality of around a quarter of the world population. However, the large-scale impact of such concentrated recharg...

Linking human activities and climate change with their consequences for water availability is a prerequisite for sustainable water management, which is traditionally performed at topographically delineated catchments. However, inter-catchment groundwater flow results in effective catchment sizes other than sizes suggested by topography. Here, we in...

Moving the study domain in hydrology to larger and larger regions leaves us with significant knowledge gaps because we are unable to observe the hydrology of many parts of the world, while in-depth hydrologic studies cover only a fraction of our landscape. On medieval maps, knowledge gaps were shown as images of lions. How do we best acknowledge an...

Model assessment is a crucial part of hydrological modelling studies. The traditional intuitive approach is to judge model performance to explore its effectiveness and informativeness about the system reality. However, this approach does not necessarily guarantee that one captures system hydrological functioning from the model output. Here, we prop...

I further evolved a semi-distrusted numerical model to enable the simulation of tracer breakthrough curves at different hydrological conditions. As a study site the highly karstified catchment of the Unica springs, covering a recharge area of 820 km², was used. The results of the model provided additional information about the complex recharge beha...

Karst groundwater constitutes a considerable fraction of drinking water in many regions in the world. Understanding its recharge processes is important for a sustainable water resource management. Experimental approaches to study karst aquifers mostly focus on the characterization of the entire aquifer using the disintegration of its output signal...

Quantifying the combination of climatic and hydrological conditions required to generate groundwater recharge is challenging, yet of fundamental importance for groundwater resource management. Here we demonstrate a new unsaturated zone physical method of determining rainfall-recharge thresholds in karst using a regional cave drip water monitoring n...

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...

Hydrological research is often focused at the catchment scale; but there are significant benefits from taking a broader spatial perspective (i.e. comparative hydrology) to advance understanding of hydrological processes, especially in the context of global change. Indeed, many of the recently described ‘unsolved problems in hydrology’ (Blöschl et a...

Karstic groundwater systems are often investigated by a combination of environmental or artificial tracers. One of the major downsides of tracer‐based methods is the limited availability of tracer measurements, especially in data sparse regions. This study presents an approach to systematically evaluate the information content of the available data...

Karst systems are characterized by a high subsurface heterogeneity, and their complex recharge processes are difficult to characterize. Experimental methods to study karst systems mostly focus on analysing the entire aquifer. Despite their important role in recharge processes, the soil and epikarst receive limited attention, and the few available s...