Assessment of the Impact of Climate Extremes on the Groundwater of Eastern Croatia

This paper analyzes the groundwater in the deep Quaternary aquifer of Eastern Croatia. These waters are collected at the Vinogradi Pumping Station (Osijek, Croatia) for the needs of public water supply. This research aimed to assess the impact of climate extremes, namely, high air temperatures and low rainfall, on the quantity and quality of groundwater. On the basis of data from the Vinogradi Pumping Station in the period 1987–2015, three extremely warm and low-water years were singled out. For these three years, the following were analyzed: climate diagrams, groundwater levels (in the piezometers closest to and farthest from the pumping station), and the quality of the affected groundwater. The results of this research indicate that the reaction of aquifers to the analyzed extreme climatic conditions for the observed period was manifested in the variation of the amplitude of groundwater levels by a maximum of 4–5 m. Considering the total thickness of the affected layers (60–80 m), this variation is not a concern from the point of view of water supply. As for the quality of groundwater, it was found to be of constant quality in its composition and was not affected by climatic extremes.

Tracking hidden crisis in India’s capital from space: implications of unsustainable groundwater use

National Capital Region (NCR, Delhi) in India is one of the fastest-growing metropolitan cities which is facing a severe water crisis due to increasing water demand. The over-extraction of groundwater, particularly from its unconsolidated alluvial deposits makes the region prone to subsidence. In this study, we investigated the effects of plummeting groundwater levels on land surface elevations in Delhi NCR using Sentinel-1 datasets acquired during the years 2014–2020. Our analysis reveals two distinct subsidence features in the study area with rates exceeding 11 cm/year in Kapashera—an urban village near IGI airport Delhi, and 3 cm/year in Faridabad throughout the study period. The subsidence in these two areas are accelerating and follows the depleting groundwater trend. The third region, Dwarka shows a shift from subsidence to uplift during the years which can be attributed to the strict government policies to regulate groundwater use and incentivizing rainwater harvesting. Further analysis using a classified risk map based on hazard risk and vulnerability approach highlights an approximate area of 100 square kilometers to be subjected to the highest risk level of ground movement, demanding urgent attention. The findings of this study are highly relevant for government agencies to formulate new policies against the over-exploitation of groundwater and to facilitate a sustainable and resilient groundwater management system in Delhi NCR.

Allowing the Actual Evapotranspiration Uncertainty in Hydrological Models: Coupling of Interval-Based Water Balance and METRIC Models

Against the paramount role of actual evapotranspiration (ET) in hydrological modeling, determining its values is mixed with different sources of uncertainties. In addition, estimation of ET with energy-based methods (e.g., METRIC) leads to different results with various acceptable initial and boundary conditions (such as land use and cold/hot pixels). The aim of the current research is to allow the uncertainty effects of ET as an interval-based input variable in hydrological modeling. The goal is achieved via feeding the uncertainty of computed ET values to the developed Interval-Based Water Balance (IBWB) model in terms of gray values. To this purpose, the comprehensive monthly water balance model (including surface and groundwater modules) has been revised to a new interval-based form. Moreover, the METRIC model has been used 20 times in each month of computational period to calculate the ET patterns with different hot/cold pixels to provide monthly ensemble ET values. For a comprehensive assessment, the selected water balance model has been calibrated with ensemble means of the computed ET with its classical type. The study area is a mountainous sub-basin of the Sefidrood watershed, Ghorveh-Dehgolan basin, with three alluvial aquifers in the North of Iran. Not only the paradigm shift from determinist to interval-based hydrologic structure improved the statistical metrics of the models’ responses, but also it decreased the uncertainty of the simulated streamflow and groundwater levels.

Influence of low-frequency variability on high and low groundwater levels: example of aquifers in Paris Basin

Groundwater levels (GWL) very often fluctuate over a wide range of timescales (infra-annual, annual, multi-annual, decadal). In many instances, aquifers act as low-pass filters, dampening the high-frequency variability and amplifying low-frequency variations (from multi-annual to decadal timescales) which basically originate from large-scale climate variability. In the aim of better understanding and ultimately anticipating groundwater droughts and floods, it appears crucial to evaluate whether (and how much) the very high or very low GWLs are sensitive to such low-frequency variability (LFV), which was the main objective of the study presented here. As an example, we focused on exceedance and non-exceedance of the 80 % and 20 % GWL percentiles respectively, in the Paris Basin aquifers over the 1976–2019 period. GWL time series were extracted from a database consisting of relatively undisturbed GWL time series regarding anthropogenic influence (water abstraction by either continuous or periodic pumping) over Metropolitan France. Based on this dataset, our approach consisted of exploring the effect of GWL low-frequency components on threshold exceedance and non-exceedance by successively filtering out low-frequency components of GWL signals using maximum overlap discrete wavelet transform (MODWT). Multi-annual (~7-yr) and decadal (~17-yr) variabilities were found to be the predominant LFVs in GWL signals, in accordance with previous studies in the northern France area. Filtering out these components (either independently or jointly) to (i) examine the proportion of high level (HL) and low level (LL) occurrences generated by these variabilities, (ii) estimate the contribution of each of these variabilities in explaining the occurrence of major historical events associated to well-recognized societal impacts. A typology of GWL variations in Paris Basin aquifers was first determined by quantifying the variance distribution across timescales. Four GWL variation types could be found according to the predominance of annual, multi-annual or/and decadal variabilities in these signals: decadal dominant (type iD), multi-annual and decadal dominant (type iMD), annual dominant (type cA), annual and multi-annual dominant (type cAM). We observed a clear dependence of high and low GWL to LFV for aquifers exhibiting these four GWL variation types. In addition, the respective contribution of multi-annual and decadal variabilities in the threshold exceedance varied according to the event. In numerous aquifers, it also appeared that the sensitivity to LFV was higher for LL than HL. A similar analysis was conducted on the only available long-term GWL time series which covered a hundred years. This allowed us to highlight a potential influence of multidecadal variability on HL and LL too. This study underlined the key role of LFV in the occurrence of HL and LL. Since LFV originates from large-scale stochastic climate variability as demonstrated in many previous studies in the Paris Basin or nearby regions, our results point out that i) poor representation of LFV in General Circulation Models (GCM) outputs used afterwards for developing hydrological projections can result in strong uncertainty in the assessment of future groundwater extremes (GWE), ii) potential changes in the amplitude of LFV, be they natural or induced by global climate change, may lead to substantial changes in the occurrence and severity of GWE for the next decades. Finally, this study also stresses the fact that due to the stochastic nature of LFV, no deterministic prediction of future GWE for the mid- or long term horizons can be achieved even though LFV may look periodic.

Sustainability of Water Resources in Karst Undermined by Tunneling: A Case Example

Water resources in karsts are scarce due to the high cavernosity in the otherwise low-permeability limestone rock mass. The highly variable porosity and transmissivity of karst aquifers are caused by a network of channels, caverns, and caves that typically act as water-bearing, connected vessels. Tunneling in a karst environment can severely deplete an aquifer and undermine the sustainability of water resources over the long term. A research study was carried out to elaborate and develop measures for the sustainable preservation of the water resources in a Slovenian karst, in which two approximately 7 km-long tunnels will be driven as part of the construction of the new Divača–Koper railway line. Hydrogeological site investigations were carried out with an aim to evaluate the transmissivity and spatial spreading of the karst aquifer along the route of the tunnels, including the observation of the long-term variation of the groundwater levels and trace experiments. The main findings, which are presented in this paper, were used to develop a methodology for the selection of adequate measures for tunnel construction with an aim of ensuring the sustainability of water resources in karst aquifers. The construction measures comprise limiting the inflows using injection grouting, obscuring the groundwater intake by undrained sections of the tunnel, and constructing bypasses around the tunnel to preserve the current groundwater flow regime. The presented methodology of dynamically accommodating the preventive measures to the actual hydrogeological conditions onsite is generally applicable for common cases in which the state of the karst aquifer could not be pre-determined with a sufficient accuracy of tens of meters to a meter. The spatially and temporally continuous hydrogeological investigations and decision-making charts to reduce the tunnelling’s impact on the karst aquifer are explained in detail in this paper.

Groundwater Drought Analysis under Data Scarcity: The Case of the Salento Aquifer (Italy)

Salento is a regional coastal karst aquifer located in Southern Italy with a highly complex geological, geomorphological, and hydrogeological structure. High and unruly exploitation of groundwater from licensed and unlicensed wells for irrigation and drinking purposes affects groundwater, with consequent degradation of its qualitative and quantitative status. The increased frequency of meteorological droughts and rising temperatures may only worsen the already compromised situation. The absence of complete and enduring monitoring of groundwater levels prevents the application of some methodologies, which require long time series. The analysis of climate indexes to describe the groundwater level variation is a possible approach under data scarcity. However, this approach may not be obvious for complex aquifers (in terms of scale, intrinsic properties, and boundary conditions) where the response of the groundwater to precipitation is not necessarily linear. Thus, the proposed research deals with the assessment of the response of the Salento aquifer to precipitation variability based on correlations between the Standardized Precipitation Index (SPI) and Standardized Precipitation and Evapotranspiration Index (SPEI) and groundwater levels for nine monitoring wells from July 2007 to December 2011. The study aims at evaluating the ability of the above indicators to explain the behavior of groundwater on complex aquifers. Moreover, it has the general aim to verify their more general reliable application. Results of three different correlation factors outline direct and statistically significant correlations between the time series. They describe the Salento aquifer as a slow filter, with a notable inertial behavior in response to meteorological events. The SPI 18-months demonstrates to be a viable candidate to predict the groundwater response to precipitation variability for the Salento aquifer.

Avaliação da qualidade da água em aquífero raso em Campos dos Goytacazes, Rio de Janeiro, Brasil

Diversas formas de uso e ocupação em áreas urbanas tem ocasionado impactos ambientais negativos em diferentes escalas, sendo um deles a degradação dos recursos hídricos, que tem suscitado novas discussões sobre mecanismos de alteração da água subterrânea rasa. A proposição de estratégias metodológicas eficientes a partir da identificação e dimensionamento de características hidroquímicas da água em determinado espaço geográfico, consiste em desafio oportuno a colaborar para a conservação e uso adequado. Diante desse contexto, o objetivo do trabalho é analisar a qualidade da água no aquífero raso em área urbana Campos dos Goytacazes/RJ, correlacionando com a influência de estruturas urbanas nessa dinâmica. Foram coletadas e analisadas amostras de água de 15 poços, além de dados potenciométricos, a fim de correlacionar fatores como: qualidade da água, tipo de uso por parte da população, influência do cemitério, e hidrodinâmica subsuperficial. Tais poços foram previamente espacializados, seguido da coleta e armazenamento das amostras, análise em laboratório, e interpretação a partir das diferentes variáveis que compuseram o quadro síntese para análise simplificada. Em adição, foi elaborado mapa potenciométrico a partir dos níveis freáticos encontrados, permitindo compilar os parâmetros elencados. Os resultados sugerem que o lençol freático é consideravelmente raso na área estudada, tornando os recursos hídricos mais vulneráveis. Por se tratar de uma área de múltiplos usos, como residencial, agrícola, comercial, além da presença de um cemitério, acaba por expor a região a maiores riscos de contaminação. Destaca-se que, conforme verificado em trabalho de campo, a região possui potenciais agentes poluidores, levando a um maior número de substâncias contaminantes que podem ser liberadas neste ambiente. Adicionalmente, constatou-se alteração dos padrões biológicos, físicos e químicos, com contaminações acima do valor máximo permitido em lei para os seguintes elementos: Fe, Al, Pb, Mn e P, além da presença de Escherichia coli (E. Coli). Assessment of water quality in a shallow aquifer in Campos dos Goytacazes, Rio de Janeiro, Brazil A B S T R A C TVarious forms of use and occupation in urban areas have caused negative environmental impacts at different scales, one of them being the degradation of water resources, which has given rise to new discussions on mechanisms for altering shallow groundwater. The proposition of efficient methodological strategies based on the identification and dimensioning of the hydrochemical characteristics of water in a given geographic space is an opportune challenge to collaborate for the conservation and proper use. In this context, the objective of this work is to analyze the water quality in the shallow aquifer in urban area Campos dos Goytacazes/RJ, correlating with the influence of urban structures in this dynamic. Water from 15 wells were collected and analyzed, in addition to potentiometric data, in order to correlate factors such as: water quality, type of use by the population, influence of the cemetery, and subsurface hydrodynamics. Such wells were previously spatialized, followed by collection and storage of aggregates, laboratory analysis, and interpretation based on the different variables that made up the synthetic framework for simplified analysis. In addition, a potentiometric map was drawn up from the groundwater levels found, allowing for the compilation of the listed parameters. The results obtained that the water table is considerably shallow in the studied area, making water resources more vulnerable. As it is an area with multiple uses, such as residential, agricultural, commercial, in addition to the presence of a cemetery, it ends up exposing the region to greater risks of contamination. It is noteworthy that, as verified in field work, the region has potential polluting agents, leading to a greater number of contaminants that can be released into this environment. Additionally, there was a change in biological, physical and chemical standards, with contamination above the maximum value allowed by law for the following elements: Fe, Al, Pb, Mn and P, in addition to the presence of Escherichia coli (E. Coli).Keywords: Hydrochemistry; Hydrodynamic; Shallow Aquifer; Contamination.

Groundwater Recharge Planning Using Field Survey for Talupula Mandal in Anantapur District, Andhra Pradesh, India

Groundwater is essential to the sustainability of India’s environment, economy, and living conditions because it isn’t just the primary source of domestic supply of water in rural areas, but it is also the major and most productive origin of the water. The increased demand for groundwater as a result of reduced rainfall has put a strain on groundwater resources in areas where groundwater is the primary supply of water. The main aim of this study is to identify and explore the groundwater potential zones in Talupula Mandal of 280.3 km2 in Ananthapur district in Andhra Pradesh, India with semi-arid climatic conditions. Based on the field survey approach, groundwater availability is found out in the villages. Schlumberger Vertical Electrical Sounding (VES) survey technique was used to discover the resistivity and thickness of the unmistakable layers. It was carried out in 18 randomly selected sites where groundwater plays an important role in agricultural and domestic use. The thickness and resistivity of first- and second-layer crack sites of the various layers were separated from ground data using IPI2WIN programming. Using software, graphs were plotted and groundwater potential zones were identified for recharging the groundwater. Based on the results, different models of recharge structures for the study area are identified and recommended. Hence the management of groundwater paves the way for sustainable groundwater levels.