HS8.1.7

Deep groundwater is the backbone of the regional water cycle, ensuring stream baseflow even after extended drought periods. The thicker the overlying vadose zone the more groundwater head dynamics is buffered against short-term fluctuations of groundwater recharge.  Thus deep groundwater is usually considered to be the least susceptible to climate change effects. However, the opposite is true. Long-term trends (20-41 years) of groundwater head in more than 200 wells in a 50,000 km² region in Northeast Germany have been analysed. Both increasing and decreasing trends were found, irrespective of land use, geology, etc. Factoring out local, mostly anthropogenic effects from the time series did hardly affect the results. In contrast, sign and size of long-term trends was very closely related to the degree of damping of the groundwater recharge signal. Damping was clearly related to mean depth to groundwater. The stronger the damping the more clearly groundwater head exhibited a 40-year decrease, whereas positive trends were found only for shallow groundwater sites.

A thorough analysis revealed a fundamental but widely ignored physical cause for these counter-intuitive results. From a thermodynamic perspective, seepage flux in the vadose zone can be described as dissipation of a hydrological input signal. This dissipation is subject to dispersion: The vadose zone acts as a low-pass filter due to preferential damping of the high frequency part of the input signal, recognizable by strong smoothing of soil hydrological time series at greater depth. Consequently, the smoother the time series the more probably a trend analysis would indicate a long-term monotonic increase or decrease even when no trend can be detected in the corresponding input signal. Note that in terms of spectrum analysis climate can be defined as a low-pass filtering of weather dynamics. Then it is only logical that deep groundwater as the part of the water cycle with the strongest low-pass filtering would be the first to clearly exhibit climate change signals.

This interpretation is consistent with an alternative perspective in terms of hydrological processes: The more shallow the groundwater, the more likely seepage flux will reach down to the groundwater table even after minor rain storms due to a smaller soil volume that needs to be refilled and to preferential flow. Consequently, groundwater recovers more rapidly from drought here. This holds especially true for groundwater in the riparian zone where most of the short-term response of stream discharge to rain storms is generated. In fact, none of these streams exhibited any clear trend. However, discharge in minor streams and water level in lakes at mid-slope positions already started to decline during the last decade. We would do well taking deep-groundwater dynamics as an early warning tool against climate change effects.

How to cite: Lischeid, G.: Deep groundwater – the most vulnerable part of the water cycle to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1476, https://doi.org/10.5194/egusphere-egu22-1476, 2022.

This work compares two different surrogate data-driven models in order to evaluate the effects of climate change on groundwater resources by means of an ensemble of 13 Regional Climate Models (RCM), provided within the Euro-Cordex project, under two different scenarios (RCP 4.5 and RCP 8.5). The impact was evaluated for three future periods: 2006-2035 (short term), 2036-2065 (medium term) and 2066-2095 (long term). Both approaches are based on historical data collected in northern Tuscany, covering the period 2005-2020. Historical precipitation and temperature records, observed in 18 gauging stations, and piezometric levels for 14 wells were used to build the surrogate models. The first methodology is based on a linear regression model and adopted standardized indices: the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Groundwater Index (SGI). First, for each well, the correlations between SPEIs and SGIs were investigated for the period 2005-2020. In case of meaningful correlation, linear regression equations are used to estimate SGIs as function of SPEIs. The linear regression models were then applied to predict future SGIs ​​using SPEIs computed from the data ​​provided by the RCMs projections. The second surrogate technique involves the use of a Long-Short Term Memory (LSTM) neural network. LSTM allows to work directly with climate variables and normalized groundwater levels. The LSTM network was trained using the historical precipitation and temperature time series for the period 2005-2018 as input and the normalized groundwater levels as output. Rain, temperature and piezometric level data from 2019 to 2020 were used to test the network. Subsequently, the rainfall and temperature time series ​​provided by the RCMs have been used by the LSTM to predict the future groundwater levels. The analysis highlights, for both approaches, a negative impact of climate change on the groundwater system. In particular, according to the RCP 4.5 in the medium-term period a larger reduction of groundwater availability is expected, while with the RCP 8.5 the long-term period is the most affected by a groundwater level decline.

How to cite: Tanda, M. G., Secci, D., D'Oria, M., and Todaro, V.: Assessment of the impact of climate change on groundwater resources using regional climate model projections: comparison of surrogate modeling techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12836, https://doi.org/10.5194/egusphere-egu22-12836, 2022.

Changes in groundwater storage are dominantly influenced by anthropogenic and climatic factors. In global and/or regional scale groundwater storage change studies, storage changes are often estimated using gravimetric satellite data (GRACE). However, the applicability of such analysis at basin-scale is still limited due to its relatively coarse spatial resolution of 1° x 1°. Combination of GRACE data with groundwater level monitoring observations, where available, and numerical modeling might yield more accurate results for catchment-scale studies.

In this study, we estimate the basin-scale groundwater storage change component in the data-scarce area of the Bandung groundwater basin in West Java, Indonesia, using MODFLOW. We parameterize the model using hydraulic conductivity data obtained from slug-tests, pumping-tests, and laboratory analysis. There is some historical groundwater level observation available to compare the model outputs against. The model is forced by recharge calculated with a distributed hydrological model (wflow_sbm). Groundwater abstraction is estimated based upon population density and other known water demands as reported in earlier studies. We simulate the period of 2005 to 2018, starting from an initial steady-state assumed to exist prior to 2005.

We compare the groundwater storage change observed in the model to that derived from GRACE data, which was calculated by subtracting the soil moisture change derived from the wflow_sbm simulation from the total terrestrial water storage change. The results show how the groundwater storage change estimated from the groundwater flow model can mimic both the dynamic and magnitude of that derived from GRACE in combination with wflow_sbm. The capability of groundwater modeling to estimate basin-scale groundwater storage change, validated by GRACE, unravel the opportunity of using such methods to predict the behavior of groundwater storage dynamics to the future impact of anthropogenic and climatic factor and to assist in deriving basin-scale groundwater policies and management strategies in data-scarce areas.

How to cite: Rusli, S. R., Bense, V., and Weerts, A.: Estimating basin-scale groundwater storage change component in data-scarce area of Bandung Basin, West Java, Indonesia, using groundwater modeling and GRACE data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11227, https://doi.org/10.5194/egusphere-egu22-11227, 2022.

While there have been significant advances in the understanding of drought in the surface water domain, little knowledge is available for groundwater and the interactions with surface water. In particular, few studies have been run to understand the short-term transient changes in groundwater quality since the early onset of a hydrological drought period. This contribution presents data and information on the groundwater hydrochemical and hydrodynamics changes occurring in an aquifer following the onset of an early dry season in Spring 2021 and developed in a hydrological drought period lasted until December 2021 in the alluvial plain of the Cornia River in coastal Tuscany (Italy).

The Cornia plain hosts a Holocene coastal aquifer constituted, in the investigated area, mainly by gravel in silty matrix. We monitored groundwater chemical quality and hydrodynamics in a series of multi-depth piezometers in a recharge area covering three different depths from the soil surface (i.e., 8m, 12m, and 18m) in the near of a Managed Aquifer Recharge (MAR) scheme (Caligaris et al. 2022). We monitored these piezometers alongside with the existing network of piezometers and the relations with Cornia River surface water for nine months from April 2021 (when the max groundwater head was recorded) until December 2021 (when the minimum was recorded).

Ten sampling campaigns were performed in this period, covering the early end of the annual MAR operation period in May 2021, and monitoring every fifteen days in the initial phase of the dry season. The last effective rainfall occurred on 11 May 2021. A total of about 130 water samples were collected. The concentrations of the main ions in the water samples were determined using an Ion Chromatography (IC) instrument. The concentrations of trace elements were determined using an Inductively Coupled Plasma Mass Spectrometer (ICP). The concentration of Boron in water was determined using a Microwave Plasma Atomic Emission Spectrometer (MP-AES). Physico-chemical parameters were measured in the field with a multiparametric probe. This resulted on the measurement of the spatiotemporal variation of 49 different parameters at each of the study point.

An important groundwater table decline, ranging from 6 to 10 m, was observed in this period, which brought to relevant water stress even in trees at the end of October 2021. The statistical behavior of the different parameters as well as their relationships are studied and presented to define a robust conceptual model unifying hydrochemistry and hydrodynamics in order to describe the evolution of the aquifer.

Acknowledgement

This paper is presented within the framework of the project MARSoluT (www.marsolut-itn.eu), a four-year Marie Skłodowska-Curie Actions (MSCA) Innovative Training Network (ITN) funded by the European Commission (Grant Agreement 814066).

References

Caligaris, E.; Agostini, M.; Rossetto, R. Using Heat as a Tracer to Detect the Development of the Recharge Bulb in Managed Aquifer Recharge Schemes. Hydrology 2022, 9, 14. https://doi.org/10.3390/hydrology9010014

How to cite: Caligaris, E. R., Rossetto, R., Schmidt, S., and Schueth, C.: Monitoring short-term transient groundwater hydrochemical and hydrodynamics changes following the onset of an early dry season and hydrological drought period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11520, https://doi.org/10.5194/egusphere-egu22-11520, 2022.

Aquifers play a relevant role in the mitigation of the risk due to the occurrence of drought events in the Emilia-Romagna region. In fact, their capability to store relevant volumes of water and the long time span between meteorological and groundwater droughts make aquifers an essential resource during dry periods. To mitigate the risk induced by water scarcity, in 2014 a managed recharge experiment was carried out on the River Marecchia alluvial fan. In detail, an additional volume taken from the river was diverted into a quarry lake. The lake is an outcrop of the aquifer, therefore an increase in the lake water volume produces a corresponding increase of the piezometric level in the aquifer, and therefore larger groundwater availability.

Several international experiences on the management of aquifers for civil and agricultural water supply have shown the value of the information that can be derived by running groundwater simulation models. In particular, MODFLOW, an open access groundwater simulation model developed by the United States Geological Survey, is widely applied.

The purpose of this work is to apply MODFLOW to study solutions for managing artificial recharge in the River Marecchia alluvial fan. In particular, a previous application of MODFLOW by the Regional Agency for Prevention, Environment and Energy of Emilia-Romagna (ARPAE) has been repeated by using a different model interface, ModelMuse, and additional climatic scenarios.

The work confirms the potential benefits that can be provided by a groundwater simulation model for optimizing aquifer recharge. The application confirmed that recharge may be very successful in this specific case for mitigating the impact of water withdrawals.

How to cite: Delfini, I., Montanari, A., and Chahoud, A.: Dynamic 3D modelling of the unconfined aquifer of the River Marecchia alluvial fan (Rimini), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7739, https://doi.org/10.5194/egusphere-egu22-7739, 2022.

The carboniferous aquifer of the international hydrographic district of the Scheldt river extends across three countries and administrative regions: France, Wallonia (South Belgium), Flanders (North Belgium) covering 1420 km². More than 75 million cubic meters of water are pumped every year in the considered hydrogeological system for drinking water distribution, agriculture, industry, and quarry dewatering. Stresses on groundwater resources in the aquifer are therefore important and pumping operations need to be managed adequately. Groundwater levels have been decreasing significantly due to the overexploitation of the aquifer caused by the industrial and demographic development of the region during the 20^th century. In some area the piezometric level has dropped by 90 meters between 1910 and 2010.

The transboundary aquifer is mainly composed of fractured carboniferous limestone. The aquifer is considered as unconfined in eastern part and confined below marls and chalk in the northwest area. Recharge is thus mainly observed within the unconfined area, with important lateral groundwater flows to the confined area.

Groundwater flow in the aquifer has been modelled in 3D using the finite volume calculation code MARTHE, in collaboration between the different involved entities, and using data officially exchanged between administrations. The model has been calibrated for the 1900-2017 period considering abstracted groundwater volumes, recharge calculated from precipitation and evapotranspiration data, observed piezometric levels and river flow rates, collected or reconstructed since 1900.

The model is used for predictive purpose. Simulations are performed for the next decades following several scenarios including the possible evolution of groundwater abstraction as a function of the demographic and economic development of the region, the expected climate evolution and related groundwater recharge change, the evolution of dewatering operations in stone quarries. Recently, recharge scenarios based on historical meteorological data were applied to the model to determine the impact of rainfall deficit on groundwater resources and the resilience of the aquifer. The impact has been quantified and time recovery map of the aquifer were built. Results show a recovery time difference up to twenty years between the confined and unconfined area of the aquifer.

All these simulations constitute a scientific support for the decision-makers involved in the management of this transboundary aquifer.

How to cite: Vandelois, G., Picot, G., Parmentier, M., and Goderniaux, P.: Assessing the resilience of the Carboniferous limestone transboundary aquifer (Belgium/France) to recharge deficit events and groundwater abstraction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8552, https://doi.org/10.5194/egusphere-egu22-8552, 2022.

It took several consecutive years of devastating droughts sweeping through Europe, causing substantial economic losses, for many to realise how urging it is to improve the water directives, making critical sectors like agriculture more resilient to a changing climate. Shrinking water supplies and growing demand further forced stakeholders to seek alternative sources, drawing their attention to projects previously considered economically unjustified. Therefore, water re-use and reclamation became one of the EU’s priorities fulfilling the ambitions of the European Green Deal to implement circular water management strategies. To facilitate the transition and support new legislation, in-depth research in the feasibility and environmental impacts of aquifer recharge with reclaimed wastewater is essential. The GROW project investigates this issue on multiple levels, among which the effect of reclamation of wastewater through aquifer recharge on local and regional scale groundwater levels.

At the experimental site in Kinrooi, Belgium, the groundwater levels are closely monitored with automatic submersible data loggers installed in 21 monitoring wells distributed on the investigated agricultural field and its vicinity. Data on water levels in the underlying Quaternary, porous aquifer are collected hourly and are verified through monthly manual measurements taken to ensure an unhindered operation of the infrastructure.

A distributed, transient-state flow model is used to simulate the groundwater table’s response to the effluent sub-irrigation at the desired rate. The model’s flexibility also allows making predictions of the aquifer behaviour under changing climatic conditions by augmenting the soil-water balance model with revised weather data. The model’s performance is tested against the high temporal resolution dataset obtained from the monitoring network. Attention is also paid to the experiment’s effect on the water levels in the adjacent hydrological network, while the effluent is partly rerouted from the hitherto used surface water discharge to the sub-irrigation system.

The data collected in our experiment is used to determine the capability of the aquifer to store and recover the reclaimed wastewater during drought periods. That would reduce the demand for traditional, inefficient surface irrigation and increase the climate resilience of the agricultural sector in Flanders. Together with data from similar projects carried out throughout Europe, our results can be used to facilitate long-expected EU legislation enabling circular water use. To support this process, we also investigate the impact of the re-use of treated wastewater for agriculture on groundwater quality and the public perception of this sensitive issue.

How to cite: Zawadzki, M., Speijer, L., Vandeputte, D., Su, Y., Luo, M., Gao, Y., Elskens, M., Verhoest, P., Bauwens, J., Coussement, T., Elsen, F., Raes, B., Eisenreich, S., and Huysmans, M.: Re-use of treated wastewater for irrigation and groundwater recharge: feasibility and effects on groundwater quantity at the experimental site in Kinrooi, Belgium., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9374, https://doi.org/10.5194/egusphere-egu22-9374, 2022.

Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water

KE Ramudzuli, JA Miller, T. Vennmann, A Watson and JD van Rooyen

Department of Earth Sciences, Stellenbosch University.

Unimodal wet season precipitation plays a significant role in ensuring sustainable and continuous replenishment of groundwater resources, especially in arid to semi-arid climates that only recharge during heavy rainfall events. For this reason, changes in precipitation patterns (i.e., the frequency, intensity, duration and seasonality of precipitation events) may impact the reliability and sustainability of groundwater resources. This study investigates the relationship between the stable water isotope precipitation vs groundwater composition from across different climatic zones in South Africa. The analysis was done to examine the record of evaporation recorded in the stable water isotopes of precipitation before groundwater recharge, in order to extrapolate how variable changes in climatic conditions would translate to groundwater recharge (e.g., induced evaporative loss of rainfall). Both precipitation and groundwater samples showed a strong alignment with the Global Meteoric Water Line (GMWL) and respective LMWLs with a dispersion that increased from the O- and H- isotope depleted sections towards the enriched areas. Groundwater samples generally recorded the same characteristics as wet season precipitation irrespective of whether this was winter or summer rainfall regions, and plotting with the same regionality for Local Meteoric Water Lines (LWMLs). Secondary evaporation of precipitation, noted by the deviation of groundwater samples from the GMWL and respective LMWLs, increased from the south-eastern and east coasts, which receive relatively higher precipitation amounts, towards the interior along with south and west coast of the country, which are somewhat dryer. This analysis will assist in the forecasting of future groundwater recharge patterns in response to climate change and represents an important step in assessing the impact of climate variability on groundwater sustainability.

How to cite: Ramudzuli, K. E.: Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11279, https://doi.org/10.5194/egusphere-egu22-11279, 2022.

To assess groundwater response to climate change scenarios in the context of groundwater drought it is fundamental to understand controlling periods of groundwater recharge as well response time to meteorological forcing (Hughes et al 2021, Jasechko et al 2014). 

The study aims at assessing the spatial and temporal distribution of groundwater drought events in the Baltic States over the period 1989 – 2018 as well as the meteorological and hydrological indicators associated with periods of below-normal groundwater level. A set of meteorological, hydrological and groundwater drought indices were used for the identification of significant drought events in the region. Used groundwater level time series were treated and checked for errors according to the Retike et al. (2021).

Four major drought events affecting all monitoring sites under study are identified (1992–1994, 1996–1997, 2002–2004 and 2005–2007), although, the fluctuations in groundwater level display distinct patterns which might be associated with the impact of local meteorological conditions and geological setting of particular monitoring sites such as seasonally derived recharge. It was found that meteorological drought indices (SPI, SPEI, DRI) showed the highest correlation with groundwater drought conditions rather than hydrological indices (SRI and SSRI) calculated from ERA-5 reanalysis data. FHowever, for most indices and most monitoring sites there is a one month time lag between the signal of the hydrometeorological index and the response of groundwater drought. Time series analysis of drought indices at groundwater monitoring sites demonstrated varying characteristics of the onset, duration, and propagation of drought events through different scales thus highlighting the complex nature of groundwater drought events in the Baltic State area.

This research is funded by the Latvian Council of Science, project “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”, project No. lzp-2019/1-0165.

References

Jasechko, Scott & Birks, Sandra & Gleeson, Tom & Wada, Yoshihide & Fawcett, Peter & Sharp, Zachary & McDonnell, Jeffrey & Welker, Jeff. (2014). The pronounced seasonality of global groundwater recharge. Water Resources Research. 50. 10.1002/2014WR015809.

Hughes, A. & Mansour, Majdi & Ward, Rob & Kieboom, Natalie & Allen, S. & Seccombe, David & Charlton, Matthew & Prudhomme, C. (2021). The impact of climate change on groundwater recharge: National-scale assessment for the British mainland. Journal of Hydrology. 598. 126336. 10.1016/j.jhydrol.2021.126336.

Retike, I., Bikše, J., Kalvāns, A., Dēliņa, A, Avotniece, Z., Zaadnoordijk, W.J., Jemeljanova, M., Popovs,K., Babre, A., Zelenkevičs, A., Baikovs, A. (2022) Rescue of groundwater level time series: How tovisually   identify   and   treat   errors.   Journal   of   Hydrology,   605,   127294.https://doi.org/10.1016/j.jhydrol.2021.127294

How to cite: Babre, A., Kalvāns, A., Popovs, K., Retiķe, I., Jemeļjanova, M., Avotniece, Z., and Bikše, J.: Assessment of groundwater determinative recharge seasons and their spatial distribution in the Baltic States based on response to historical drought 1989–2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11392, https://doi.org/10.5194/egusphere-egu22-11392, 2022.

The average air temperature in the world has increased recently. Over the past 20 years, the global average has increased by 0.6 C and continues to increase [1]. In south-western Poland, in Wrocław, for the same period, the recorded increase in the average air temperature is approx. 0.5 °C [2]. The reason for this phenomenon is human activity. The process of urbanisation has created another phenomenon called the Urban Heat Island (UHI), which can be studied analysing for example the Land Surface Temperature (LST). The combined effect of the UHI and climate change can influence groundwater temperature by penetrating underground. The phenomenon of elevated groundwater temperatures is called the Subsurface Urban Heat Island (SUHI) [3,4]. While the Urban Heat Island effects is generally negative and widely investigated, the higher groundwater temperature may have positive aspect, such as e.g. use in heat pumps. The SUHI phenomenon is less understood than the UHI one.
This presentation focuses on the spatial distribution of temperature in shallow aquifers in the city of Wroclaw (SW Poland) developed with various interpolation techniques and based on measurements made in a network of piezometers in the 2004-2005 period. In total 67 locations have been measured and the temperatures recorded varied between 1.1 °C and 24.5 °C with the average of 13.2 °C. The data has been processed with the IDW, spline and kriging interpolation methods. The groundwater temperature distribution was analysed spatially, taking into account the then land use and location of technical infrastructure. In addition, an attempt has been made to compare the distribution of groundwater temperature with the Land Surface Temperature. The latter was determined based on Landsat 5 satellite imagery.
The interpolated groundwater temperature maps have made it possible to analyse and present graphically the spatial distribution of temperature and link it to the LST UHI for the analysed period.

Bibliography:

[1] Global Climate Change https://climate.nasa.gov/ (accessed on 11 January 2022)

[2] Polish climate 2020. Institute of Meteorology and Water Management, National Research Institute. Available online: https://www.imgw.pl/sites/default/files/2021-04/imgw-pib-klimat-polski-2020-opracowanie-final-pojedyncze-min.pdf. (accessed on 11 January 2022)

[3] Luo Z., Asproudi C., Subsurface urban heat island and its effects on horizontal ground-source heat pump potential under climate change, Applied Thermal Engineering, Volume 90, 2015, doi: 10.1016/j.applthermaleng.2015.07.025.

[4] Zhu, K., Bayer, P., Grathwohl, P., and Blum, P. (2015), Groundwater temperature evolution in the subsurface urban heat island of Cologne, Germany, Hydrol. Process., 29, 965– 978, doi: 10.1002/hyp.10209

How to cite: Blachowski, J. and Hajnrych, M.: Groundwater temperature study - Subsurface Urban Heat Island in the city of Wrocław (Poland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8483, https://doi.org/10.5194/egusphere-egu22-8483, 2022.