Christian Moeck

Tutorials as a flexible alternative to GUIs

Environmental modelling software with graphical user interfaces (GUIs) are user friendly and help to focus on the aspects of modelling rather than on the technicality of the underlying code. This is a fundamental advantage compared to codes without a GUI, as the absence of a GUI can prohibit the widespread application of a software tool. However, there is a downside to GUIs, too. They commonly lag behind the newest software development. We argue that tutorials are a flexible but undervalued alternative to GUIs, and are convinced that tutorials can help to make complex software accessible to an increased number of users. As an example to demonstrate our point, we have written a tutorial that illustrates the use of Pilot-Point based calibration made available through PEST in the HydroGeoSphere modelling environment. We hope that this example will encourage the modelling community to develop tutorials and make them available to the wider public. Workflow and tutorial are provided for employing the Pilot Points method without a GUI.We demonstrate the application of Pilot Points calibration with HydroGeoSphereWe compare methods to identify dependence of estimated parameters on observations.

The influence of model structure on groundwater recharge rates in climate-change impact studies

Numerous modeling approaches are available to provide insight into the relationship between climate change and groundwater recharge. However, several aspects of how hydrological model choice and structure affect recharge predictions have not been fully explored, unlike the well-established variability of climate model chains—combination of global climate models (GCM) and regional climate models (RCM). Furthermore, the influence on predictions related to subsoil parameterization and the variability of observation data employed during calibration remain unclear. This paper compares and quantifies these different sources of uncertainty in a systematic way. The described numerical experiment is based on a heterogeneous two-dimensional reference model. Four simpler models were calibrated against the output of the reference model, and recharge predictions of both reference and simpler models were compared to evaluate the effect of model structure on climate-change impact studies. The results highlight that model simplification leads to different recharge rates under climate change, especially under extreme conditions, although the different models performed similarly under historical climate conditions. Extreme weather conditions lead to model bias in the predictions and therefore must be considered. Consequently, the chosen calibration strategy is important and, if possible, the calibration data set should include climatic extremes in order to minimise model bias introduced by the calibration. The results strongly suggest that ensembles of climate projections should be coupled with ensembles of hydrogeological models to produce credible predictions of future recharge and with the associated uncertainties.RésuméDe nombreuses approches de modélisation sont disponibles pour fournir un aperçu de la relation entre le changement climatique et la recharge des eaux souterraines. Cependant, plusieurs aspects relatifs sur la façon dont le choix du modèle hydrologique et de sa structure affectent les prévisions en termes de recharge n’ont pas été entièrement explorés, contrairement à la variabilité bien établie des chaînes de modèles climatiques—combinaison de modèles climatiques globaux (GCM) et des modèles climatiques régionaux (RCM). En outre, l’influence sur les prévisions liées à la paramétrisation du sous-sol et à la variabilité des données d’observation employées lors de la calibration restent peu claires. Cet article compare et quantifie ces différentes sources d’incertitude de façon systématique. L’expérience numérique décrite est basée sur un modèle hétérogène de référence en deux dimensions. Quatre modèles les plus simples ont été calibrés par rapport à la sortie du modèle de référence et les prévisions de recharge des modèles de référence et des modèles les plus simples ont été comparées afin d’évaluer l’effet de la structure du modèle sur les études d’impact du changement climatique. Les résultats mettent en évidence que la simplification du modèle conduit à des taux de recharge différents pour un changement climatique, en particulier pour des conditions extrêmes, bien que les différents modèles donnent des résultats similaires pour des conditions climatiques historiques. Les conditions météorologiques extrêmes conduisent à modéliser un biais dans les prévisions et doivent donc être prises en considération. Par conséquent, la stratégie de calibration choisie est très importante et, si possible, l’ensemble des données d’étalonnage devrait inclure des conditions climatiques extrêmes afin de minimiser les biais du modèle introduit par la calibration. Les résultats suggèrent fortement que des ensembles de projections climatiques devraient être couplés avec des ensembles de modèles hydrogéologiques pour produire des prévisions crédibles de recharge future et avec les incertitudes associées.ResumenNumerosos métodos de modelado están disponibles para dar una idea de la relación entre el cambio climático y recarga del agua subterránea. Sin embargo, no se han explorado a fondo varios aspectos de cómo elegir el modelo hidrológico y cómo la estructura afecta las predicciones de recarga, a diferencia de la variabilidad bien establecida de cadenas de modelos climáticos—combinación de los modelos globales del clima (GCM) y los modelos climáticos regionales (MCR). Por otra parte, la influencia en las predicciones relacionadas con la parametrización del subsuelo y la variabilidad de los datos de observación empleados durante la calibración siguen sin estar claros. Este artículo compara y cuantifica estas diferentes fuentes de incertidumbre de una manera sistemática. El experimento numérico descripto se basa en un modelo de referencia heterogéneo de dos dimensiones. Se calibraron cuatro modelos sencillos contra la salida del modelo de referencia y las predicciones de la recarga de los modelos de referencia más simples y se compararon para evaluar el efecto de la estructura del modelo en estudios de impacto del cambio climático. Los resultados ponen de manifiesto que un modelo simplificado conduce a diferentes ritmos de recarga bajo el cambio climático, especialmente en condiciones extremas, aunque los diferentes modelos de comportamiento sean similares para condiciones climáticas históricas. Las condiciones climáticas extremas llevan a modelar el sesgo en las predicciones y por lo tanto deben ser consideradas. En consecuencia, la estrategia de calibración elegida es muy importante y, si es posible, el conjunto de datos de calibración debe incluir los extremos climáticos con el fin de minimizar el modelo de sesgo introducido en la calibración. Los resultados sugieren fuertemente que los conjuntos de proyecciones climáticas deben ir acompañados de conjuntos de modelos hidrogeológicos para producir predicciones creíbles de la futura recarga y con las incertidumbres asociadas.摘要现有许多模拟方法可以深入了解气候变化和地下水之间的关系。然而,和气候模型链(全球气候模型和区域气候模型的组合)已经得到确认下来的可变性不同,水文模型的选择和结构是怎样影响补给预测的几个方面还没有充分研究过。另外,对与下层土壤参数化有关的预测的影响及校准中使用的观测资料的可变性仍然不清楚。本文系统地比较和量化了这些不同的不确定源。所描述的数值实验基于异质性二维参考模型。针对参考模型的输出项,对四个更简单的模型进行了校准,对更简单模型和参考模型的补给预测结果进行了比较,以评估模型结构对气候变化影响研究的效果。研究强调了模型简单化会导致在气候变化下特别是在极端条件下的不同补给率,尽管不同的模型在历史气候条件下表现相似。极端天气状况导致预测中模型偏差,因此必须加以考虑。所以,选择的校准策略相当重要,如果可能的话,校准数据集应该包括气候极端值,以便使校准带来的模型偏差降低到最小。结果显示,气候预测的总体效果应当与水文地质模型的总体效果耦合,得出将来补给的可靠预测结果,同时,气候预测的总体效果也要与相关不确定性耦合。ResumoInúmeras abordagens de modelagem estão disponíveis para prover conhecimento sobre a relação entre mudança climática e recarga das águas subterrâneas. Entretanto, alguns aspectos de como a escolha e a estrutura do modelo hidrológico afeta as estimativas de recarga não foram totalmente explorados, ao contrário da variabilidade bem estabelecida das correntes de modelagem climática—combinação de modelos climáticos globais (MCG) e modelos climáticos regionais (MCR). Além disso, a influência nas estimativas relacionada a parametrização do subsolo e a variabilidade nos dados observados empregados durante a calibração permanecem sem clareza. Esse trabalho compara e quantifica essas diferentes fontes de incerteza de uma forma sistemática. O experimento numérico descrito foi baseado em um modelo de referência bidimensional homogêneo. Quatro modelos mais simples foram calibrados em comparação ao resultado de saída do modelo de referência, e as estimativas de recarga para o modelo de referência e os modelos mais simples foram comparados para avaliar o efeito da estrutura do modelo nos estudos sobre impactos da mudança climática. Os resultados destacaram que a simplificação do modelo leva à diferentes taxas de recarga sob mudança climática, especialmente sob condições extremas, embora esses modelos tenham performances similares sob condições climáticas históricas. Condições climáticas extremas deixam o modelo tendencioso nas predições e devem ser consideradas. Consequentemente, a estratégia de calibração escolhida é importante e, se possível, o conjunto de dados de calibração devem incluir extremos climáticos para minimizar a tendência do modelo introduzida pela calibração. Os resultados sugerem fortemente que conjuntos de projeções climáticas devem ser acoplados com os conjuntos de modelos hidrogeológicos para produzir estimativas confiáveis de recargas futuras e com incertezas associadas.

Assessing groundwater quality trends in pumping wells using spatially varying transfer functions

When implementing remediation programs to mitigate diffuse-source contamination of aquifers, tools are required to anticipate if the measures are sufficient to meet groundwater quality objectives and, if so, in what time frame. Transfer function methods are an attractive approach, as they are easier to implement than numerical groundwater models. However, transfer function approaches as commonly applied in environmental tracer studies are limited to a homogenous input of solute across the catchment area and a unique transfer compartment. The objective of this study was to develop and test an original approach suitable for the transfer of spatially varying inputs across multiple compartments (e.g. unsaturated and saturated zone). The method makes use of a double convolution equation accounting for transfer across two compartments separately. The modified transfer function approach was applied to the Wohlenschwil aquifer (Switzerland), using a formulation of the exponential model of solute transfer for application to subareas of aquifer catchments. A minimum of information was required: (1) delimitation of the capture zone of the outlet of interest; (2) spatial distribution of historical and future pollution input within the capture zone; (3) contribution of each subarea of the recharge zone to the flow at the outlet; (4) transfer functions of the pollutant in the aquifer. A good fit to historical nitrate concentrations at the pumping well was obtained. This suggests that the modified transfer function approach is suitable to explore the effect of environmental projects on groundwater concentration trends, especially at an early screening stage.RésuméLors de la mise en œuvre de programmes de lutte contre les pollutions diffuses des aquifères, des outils sont nécessaires pour déterminer si les mesures mises en œuvre seront suffisantes pour atteindre les objectifs de qualité des eaux souterraines et, si oui, à quelle échéance temporelle. Les méthodes par fonction de transfert constituent une approche attractive car elles sont à priori plus faciles à mettre en œuvre que les modèles numériques de nappe. Cependant, les approches par fonction de transfert, appliquées couramment dans les études utilisant des traceurs environnementaux, sont limitées à un apport homogène de soluté sur tout le bassin versant et à un unique compartiment de transfert. L’objectif de cette étude est de développer et tester une approche originale adaptée pour le transfert de polluants entrant variant spatialement, et s’écoulant au travers de compartiments multiples (par exemple zones non saturée et saturée). La méthode utilise une équation de double convolution représentant séparément le transfert à travers deux compartiments. L’approche par fonction de transfert modifiée a été appliquée à l’aquifère de Wohlenschwil (Suisse), en utilisant une formulation du modèle exponentiel pour le transfert de soluté avec application à des sous-zones des bassins versants de l’aquifère. Un minimum d’information était requis : (1) délimitation de la zone d’appel du puits d’intérêt ; (2) distribution spatiale d’infiltrations passées et futures de pollution au sein de la zone d’appel ; (3) contribution de chaque sous-zone de la zone de recharge au débit au puits ; (4) fonctions de transfert du polluant dans l’aquifère. Un bon calage avec les historiques de concentrations en nitrate au puits de pompage a été obtenu. Cela suggère que l’approche par fonction de transfert modifiée est adaptée pour explorer les effets des projets environnementaux sur les tendances d’évolution des concentrations au sein des eaux souterraines, particulièrement dans une étape préliminaire au projet.ResumenCuando se implementan programas de remediación para mitigar la contaminación de fuentes difusas en los acuíferos, se requieren herramientas para anticipar si las medidas son suficientes para satisfacer con los objetivos de la calidad de las aguas subterráneas y, en caso afirmativo, en qué plazos. Los métodos de función de transferencia son un enfoque atractivo, ya que son más fáciles de implementar que los modelos numéricos de agua subterránea. Sin embargo, el enfoque de la función de transferencia tal como son aplicadas comúnmente en estudios de seguimiento ambiental se limita a una entrada homogénea de solutos a través de la zona de captación y un único compartimento de transferencia. El objetivo de este estudio fue desarrollar y probar un enfoque original apropiado para la transferencia de las entradas espacialmente variables a través de múltiples compartimentos (por ejemplo zona no saturada y zona saturada). El método hace uso de una ecuación doble de convolución que tiene en cuenta la transferencia a través de dos compartimentos por separado. El enfoque de la función de transferencia modificada se aplicó al acuífero Wohlenschwil (Suiza), usando una formulación de un modelo exponencial de la transferencia de soluto para la aplicación a las subáreas de las cuencas de captación de acuíferos. Se requirió un mínimo de información: (1) la delimitación de la zona de captación de la salida de interés; (2) la distribución espacial de la entrada histórica y futuras de contaminantes dentro de la zona de captación; (3) la contribución de cada subzona de la zona de recarga para el flujo en la salida; (4) funciones de transferencia de contaminantes en el acuífero. Se obtuvo un buen ajuste a las concentraciones históricas de nitratos en el pozo de bombeo. Esto sugiere que el enfoque de la función de transferencia modificada es adecuado para explorar el efecto de los proyectos ambientales sobre las tendencias de concentración de las aguas subterráneas, especialmente en una etapa de detección temprana.摘要当实施修复项目以减缓含水层扩散源污染时,如果采取的措施足够满足地下水水质目标,就需要工具进行预测,要是这样,就需要在什么样的时间框架下进行预测。传递函数方法是一个有吸引力的方法,因为其方法比数值地下水模型更容易实施。然而,通常应用在环境示踪研究的传递函数方法受限于汇水区溶质的均匀性输入及独特的传递区划。本研究的目的就是开发和测试适合穿过多区划(例如非饱和带和饱和带)空间上变化的输入项传递的由独创性的方法。方法使用一个双卷积方程,这个双卷积方程可导出分别穿过两个区划的传递。采用应用在含水层汇水区亚区的溶质传递指数模型公式,把改进的传递函数方法用在了(瑞士)Wohlenschwil含水层上。需要的至少信息:1)相关出口捕获带的界定;2)捕获带内过去和将来污染输入的空间分布;3)补给带每个亚区对出口处水流的贡献量;4)含水层中污染物的传递函数。发现对抽水井历史硝酸盐含量拟合的非常好。这表明改进的传递函数方法适合探索环境项目对地下水污染物含量趋势的影响,特别是在屏蔽早期。ResumoNa implementação de programas de remediação para mitigar contra fontes difusas de contaminação em aquíferos, são necessárias ferramentas para antecipar se as medidas são suficientes para alcançar os padrões de qualidade da água e, nesse caso, em qual período de tempo. Métodos de funções de transferência são uma abordagem atraente, uma vez que eles são mais simples de se implementar do que modelos numéricos de águas subterrâneas. Entretanto, abordagens de funções de transferência comumente aplicadas como estudos ambientais de traçadores são limitados a entradas homogêneas de solutos através da área de captação e um único compartimento de transferência. O objetivo desse estudo foi desenvolver e testar uma abordagem original apropriada para a transferência de entradas espacialmente variante através de múltiplos compartimentos (p. ex. zonas não saturadas e saturadas). O método faz uso de uma equação de dupla convolução considerada para transferência através de dois compartimentos separados. A abordagem de função de transferência modificada foi aplicada ao aquífero Wohlenschwil (Suíça), utilizando a formulação de um modelo exponencial para transferência de soluto para aplicação a subáreas de captação do aquífero. A mínima informação requerida foi: (1) delimitação da zona de captura da saída de interesse; (2) distribuição espacial das entradas de poluição históricas e futuras da saída de interesse; (3) contribuição e cada subárea da zona de recarga para o fluxo na saída; (4) funções de transferência do poluente no aquífero. Um bom ajuste às concentrações históricas de nitrato no poço de bombeamento foi obtido. Isso sugere que a abordagem de função de transferência modificada é apropriada para explorar o efeito de projetos ambientais em tendências de concentrações de águas subterrâneas, especialmente nos estágios de rastreamento iniciais.

Characterization of a managed aquifer recharge system using multiple tracers

Knowledge about the residence times of artificially infiltrated water into an aquifer and the resulting flow paths is essential to developing groundwater-management schemes. To obtain this knowledge, a variety of tracers can be used to study residence times and gain information about subsurface processes. Although a variety of tracers exists, their interpretation can differ considerably due to subsurface heterogeneity, underlying assumptions, and sampling and analysis limitations. The current study systematically assesses information gained from seven different tracers during a pumping experiment at a site where drinking water is extracted from an aquifer close to contaminated areas and where groundwater is artificially recharged by infiltrating surface water. We demonstrate that the groundwater residence times estimated using dye and heat tracers are comparable when the thermal retardation for the heat tracer is considered. Furthermore, major ions, acesulfame, and stable isotopes (δ2H and δ18O) show that mixing of infiltrated water and groundwater coming from the regional flow path occurred and a vertical stratification of the flow system exist. Based on the concentration patterns of dissolved gases (He, Ar, Kr, N2, and O2) and chlorinated solvents (e.g., tetrachloroethene), three temporal phases are observed in the ratio between infiltrated water and regional groundwater during the pumping experiment. Variability in this ratio is significantly related to changes in the pumping and infiltration rates. During constant pumping rates, more infiltrated water was extracted, which led to a higher dilution of the regional groundwater. An infiltration interruption caused however, the ratio to change and more regional groundwater is extracted, which led to an increase in all concentrations. The obtained results are discussed for each tracer considered and its strengths and limitations are illustrated. Overall, it is demonstrated that aquifer heterogeneity and various subsurface processes necessitate application of multiple tracers to quantify uncertainty when identifying flow processes.

Estimating the spatial distribution of artificial groundwater recharge using multiple tracers

ABSTRACT Stable isotopes of water, organic micropollutants and hydrochemistry data are powerful tools for identifying different water types in areas where knowledge of the spatial distribution of different groundwater is critical for water resource management. An important question is how the assessments change if only one or a subset of these tracers is used. In this study, we estimate spatial artificial infiltration along an infiltration system with stage–discharge relationships and classify different water types based on the mentioned hydrochemistry data for a drinking water production area in Switzerland. Managed aquifer recharge via surface water that feeds into the aquifer creates a hydraulic barrier between contaminated groundwater and drinking water wells. We systematically compare the information from the aforementioned tracers and illustrate differences in distribution and mixing ratios. Despite uncertainties in the mixing ratios, we found that the overall spatial distribution of artificial infiltration is very similar for all the tracers. The highest infiltration occurred in the eastern part of the infiltration system, whereas infiltration in the western part was the lowest. More balanced infiltration within the infiltration system could cause the elevated groundwater mound to be distributed more evenly, preventing the natural inflow of contaminated groundwater. Dedicated to Professor Peter Fritz on the occasion of his 80th birthday

Improved water resource management for a highly complex environment using three-dimensional groundwater modelling

A three-dimensional groundwater model was used to improve water resource management for a study area in north-west Switzerland, where drinking-water production is close to former landfills and industrial areas. To avoid drinking-water contamination, artificial groundwater recharge with surface water is used to create a hydraulic barrier between the contaminated sites and drinking-water extraction wells. The model was used for simulating existing and proposed water management strategies as a tool to ensure the utmost security for drinking water. A systematic evaluation of the flow direction between existing observation points using a developed three-point estimation method for a large number of scenarios was carried out. It is demonstrated that systematically applying the developed methodology helps to identify vulnerable locations which are sensitive to changing boundary conditions such as those arising from changes to artificial groundwater recharge rates. At these locations, additional investigations and protection are required. The presented integrated approach, using the groundwater flow direction between observation points, can be easily transferred to a variety of hydrological settings to systematically evaluate groundwater modelling scenarios.RésuméUn modèle tridimensionnel d’eau souterraine a été utilisé pour améliorer la gestion des ressources en eau pour une zone d’étude dans le Nord-Ouest de la Suisse, où la production d’eau potable est à proximité d’anciens sites d’enfouissement et des zones industrielles. Pour éviter la contamination de l’eau potable, la recharge artificielle des eaux souterraines avec de l’eau de surface est utilisée pour créer une barrière hydraulique entre les sites contaminés et les puits d’exploitation d’eau potable. Le modèle a été utilisé pour simuler les stratégies existantes et proposées de gestion de la ressource en eau comme outil pour assurer la plus grande sécurité pour l’eau potable. Une évaluation systémique de la direction des écoulements entre les piézomètres existants en utilisant une méthode d’estimation à trois points développée pour un grand nombre de scénarios a été réalisée. Il est démontré que l’application systématique de la méthodologie développée aide à identifier les endroits vulnérables qui sont sensibles aux changements des conditions aux limites, telles que celles résultant des changements de taux de recharge artificielle des eaux souterraines. Dans ces endroits, des études et protection complémentaires sont requises. L’approche intégrée présentée, en utilisant la direction de l’écoulement des eaux souterraines entre les piézomètres, peut être facilement transférée à une variété de contextes hydrogéologiques pour évaluer de manière systématique des scénarios de modélisation des eaux souterraines.ResumenSe utilizó un modelo tridimensional de agua subterránea para mejorar la gestión de los recursos hídricos de un área de estudio en el noroeste de Suiza, donde la producción de agua potable está cerca de los antiguos vertederos de residuos y zonas industriales. Para evitar la contaminación del agua potable, la recarga artificial de agua subterránea con agua superficial se utiliza para crear una barrera hidráulica entre los sitios contaminados y los pozos de extracción de agua potable. El modelo se utilizó para simular las estrategias existentes y propuestas de gestión del agua como una herramienta para garantizar la máxima seguridad para el agua potable. Se llevó a cabo una evaluación sistemática de la dirección del flujo entre puntos de observación existentes utilizando un método de estimación de tres puntos desarrollado para un gran número de escenarios. Se demuestra que la aplicación sistemática de la metodología desarrollada ayuda a identificar lugares vulnerables que son sensibles a las condiciones cambiantes de los límites, como los que surgen de los cambios en las tasas de recarga artificial de agua subterránea. En estos lugares, se requieren investigaciones adicionales y de protección. El enfoque integrado que se presenta, que utiliza la dirección del flujo de agua subterránea entre los puntos de observación, puede transferirse fácilmente a una variedad de ambientes hidrológicos para evaluar sistemáticamente los escenarios a partir del modelado del agua subterránea.摘要在瑞士西北部一个研究区,饮用水生产靠近过去的填埋场及工业区,在这里利用三维地下水模型提高水资源的管理水平。为了避免饮用水遭到污染,采用地表水人工补给地下水,在污染的场地和饮用水抽水井之间构建水力屏障。模型用作进行模拟现有的和建议的水管理策略的工具,以确保饮用水的绝对安全。利用开发出的针对各种不同方案的三点估算法对现有观测点之间的水流方向进行了系统评估。证明系统应用开发的方法有助于确定易受物探的位置,这些位置对变化的边界条件诸如人工地下水补给量导致的边界变化非常敏感。在这些位置,需要进行额外的调查和保护。所展示的利用观测点之间水流方向的综合方法可容易地应用到各种水文地质背景下,系统地评估地下水模拟方案。ResumoUm modelo tridimensional de águas subterrâneas foi utilizado para aprimorar o gerenciamento de recursos hídricos para uma área de estudo no noroeste da Suíça, onde a produção de água potável está próxima de antigos aterros e áreas industriais. Para evitar a contaminação da água potável, a recarga artificial de águas subterrâneas com água superficial é utilizada para criar uma barreira hidráulica entre os locais contaminados e os poços de extração de água potável. O modelo foi utilizado para simular estratégias existentes e propostas de gerenciamento da água, como uma ferramenta para garantir a máxima segurança para a água potável. Foi realizada uma avaliação sistemática da direção do fluxo entre os pontos de observação existentes utilizando um método de estimativa de três pontos desenvolvido para um grande número de cenários. Demonstra-se que a aplicação sistemática da metodologia desenvolvida ajuda a identificar locais vulneráveis que são sensíveis a modificações nas condições de contorno, tais como os decorrentes de mudanças nas taxas de recarga artificial de água subterrânea. Nesses locais, são necessárias investigações adicionais e proteção. A abordagem integrada apresentada, utilizando a direção do fluxo das águas subterrâneas entre os pontos de observação, pode ser facilmente transferida a uma variedade de configurações hidrológicas para avaliar sistematicamente cenários de modelagem de águas subterrâneas.

Groundwater recharge predictions in contrasted climate: The effect of model complexity and calibration period on recharge rates

We systematically evaluated the effect of model complexity and calibration strategy on estimated recharge using four varyingly complex models and a unique long-term recharge data set. A differential split sample test was carried out by using six calibration periods with climatically contrasting conditions in a constrained Monte Carlo approach. All models performed better during calibration than during validation due to differences in model structures and climatic conditions. The two more complex, physically-based models predicted the observed recharge with relatively small uncertainties, even when calibration and prediction periods had different climatic conditions. In contrast, the more simplistic soil-water balance model significantly underestimated the recharge rates. The fourth, semi-mechanistic model captured the observed recharge rates, but with a larger uncertainty range than the physically-based models. Our results may have relevant implications for a broad range of applications when recharge models are used as decision-making tools. Model performance is a function of the complexity of the chosen recharge model.Chosen calibration period becomes important when simplistic recharge models are used.Models performed best when validation period is very similar to the calibration period.No optimal calibration period allowing for equally good simulations with all models.Best results were obtained for the most contrasting calibration period.