Groundwater sustainability in a changing climate: modeling and experimental analyses from urban, agricultural and ecological contexts

Groundwater is arguably the most strategic freshwater resource for humans and the biosphere. If properly managed, groundwater can be resilient to climate change, making it a valuable resource to protect and optimize for climate change mitigation plans. Yet, groundwater can be also vulnerable to antropic contamination and naturally a poorly renewable resource, requiring our efforts to ensure its long-term sustainability. This session gathers theoretical and applied studies focusing on groundwater sustainability. The session welcomes experimental and modeling tools and analyses performed from the shallow soils and vadose zone to deeper environmental studies, including fossil aquifers. Among the topics, the session addresses:
• the development and use of modern techniques, such as managed aquifer recharge (MAR);
• the optimization of pumping wells and draining systems;
• the optimization of groundwater-driver irrigation and other agricultural applications;
• the sustainable use of groundwater to save groundwater-dependent ecosystems; including rivers and streams endangered by aquifer overexploitation, and;
• the disturbance of external factors, such as wildfires.
The results and discussions emerging from this session will help disentangling some of the "23 Unsolved Problems in Hydrology", in particular climate-change-driven time variability (questions 1-4), the role of different interfaces in hydrology to control the management of groundwater (questions 12-15) and the impact of groundwater sustainability on the society (questions 21-23).

Convener: Daniele Pedretti | Co-Conveners: Michelle Newcomer, Barry Croke, Amir AghaKouchak
| Fri, 03 Jun, 13:30–17:45|Room Barthez 2
| Attendance Fri, 03 Jun, 15:00–16:30|Poster area

Orals: Fri, 03 Jun | Room Barthez 2

Chairpersons: Barry Croke, Daniele Pedretti, Amir AghaKouchak
Pierre Séraphin, Julio Gonçalvès, Bruno Hamelin, Thomas Stieglitz, and Pierre Deschamps

This study assesses the detailed water budget of the Saq-Ram Aquifer System (520 000 km²) over the 2002-2019 period using satellite-gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions (JPL, CSR, GSFC) were tested for their local compatibility to compute groundwater storage variations in combination with soil moisture datasets (VIC, CLSM, NOAH) available from the Global Land Data Assimilation System (GLDAS) land surface models. Accounting for groundwater pumping (15.7 ± 1.1 mm yr-1), artificial recharge (2.2 ±

0.8 mm yr-1) and natural discharge (0.3 ± 0.06 mm yr-1) uniformly distributed over the Saq-Ram domain, the GRACE-derived water mass balance calculation yields a long-term estimate of the domain-averaged natural recharge of 2.4 ± 1.4 mm yr-1, corresponding to 4.4 ± 2.6% of the annual average rainfall.

Beyond the global approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin. Within agricultural plots, irrigation excess is great enough to artificially recharge the aquifer (i.e. 167 ± 83 mm yr-1 distributed over irrigated areas). However, on the outskirts of these crop areas subjected only to the natural recharge but still influenced by pumping drawdown, there is a risk of relative disconnection from the infiltration front with the declining water table (i.e.  the unsaturated zone thickens faster than percolation flows through it), making effective recharge locally zero. The second source of recharge heterogeneity identified here is natural: Volcanic lava deposits (called Harrats on the Arabian Peninsula) which cover 8% of the Saq-Ram Aquifer domain but contribute to more than 50% of the total natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge which has been poorly discussed hitherto.

How to cite: Séraphin, P., Gonçalvès, J., Hamelin, B., Stieglitz, T., and Deschamps, P.: Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq-Ram, Arabian Peninsula), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-102, 2022.

Youcef Hakimi, Philippe Orban, Pierre Deschamps, and Serge Brouyère

The Continental Intercalaire aquifer (CI) (North Africa) is one of the largest transboundary aquifer systems in the world. It contains around 20 000 × 109 m3 of groundwater. The recharge comes mainly from the occidental part of the aquifer (southern foothills of the Saharan Atlas, Algeria) going east to the outlet area in South Tunisia. Several studies have showed, using 14C, that the principal recharge has taken place in Late Pleistocene and Holocene. However, doubts exist about the results of some of these studies as it was demonstrated that samples containing less than 10pmc could have been contaminated by modern air during the sampling procedure.

Based on a new field survey and the combination of new 14C and 36Cl data, the data of the previous studies are reviewed and new insights on the groundwater age are given. Close to recharge area, 14C age showed a significant amount of modern recharge (less than 2Ky B.P.). Any sample was found to have an age between 2 to 11Ky P.B. This means that during this period, Northern Sahara was dominated by a hyperarid climate. From 11 to 30Ky, it is observed that there is cyclicity of approximately 4Ky between given ages. This indicates that this period is dominated by an arid climate. Those 14C ages are calculated using F&G model.

Beyond 30 Ky P.B., the use 14C is critical because of its limited half-time. 36Cl is more relevant in that case (half-time equal to 301Ky). Samples close to recharge area, where 14C activities are sufficiently high and halite dissolution is not significant, are explored in order to define initial values of 36Cl. There, the initial 36Cl/Cl ratio is around 145 × 10-15 at/at and the initial chlorine concentration is around 175mg/L. Based on these values, the age of CI groundwater in the Great Oriental Erg basin and South Tunisia has to be 300 to 700Ky old instead of 40 to 50Ky calculated by 14C. This is supported by the ages calculated by 81Kr performed in the South Tunisia. However, the applicability limit of each technic has to be investigated.

How to cite: Hakimi, Y., Orban, P., Deschamps, P., and Brouyère, S.: Review of groundwater age of a transboundary aquifer system using 14C and 36Cl, case of the Continental Intercalaire aquifer in Algerian Sahara and Southern Tunisia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-56, 2022.

Dr. Kartic Bera, Dr. Michelle E. Newcomer, and Prof. Pabitra Banik

Drylands are characterized by their limited water supply, low and highly variable rainfall, and recurrent drought. Almost 40% of land in the world is considered drylands, which are the most sensitive areas to climate change and human activities. Representative Concentration Pathways (RCPs) projections data show an increase of drylands by 50% near the end of this century. With the expansion of drylands, and the increasing population in West Bengal (85° 40'E-88° 15'E longitudes and 21° 45'N-24° 45'N latitude), this puts pressure on water managers to accurately plan, prepare, and implement new measures for increasing water sustainability and sources of water. Future climate projections will require finding alternative and reusable water sources for present and future use. The goal of this study is to design a methodology to evaluate current existing groundwater resources, and to identify future potential zone for artificial groundwater recharge activities to improve groundwater storage during rain events. We also evaluate locations for rainwater harvesting, the state-of-the science of wastewater reuse and alternative crop rotations to minimize water use while maximizing production and benefits to farmers. Our work is applicable to other dryland areas around the world experiencing accelerated warming and desertification. 

How to cite: Bera, Dr. K., E. Newcomer, Dr. M., and Banik, P. P.: Climate Risk Analysis for Water Resources in Dryland Area of West Bengal, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-157, 2022.

Nazeer Asmael and Alain Dupuy

The Garonne river is the third longest river in France and the most important one for the southwest part of the country. Its hydrology is influenced by the Mediterranean and oceanic climate and the snow melt. The surrounding Quaternary alluvial aquifer is considered as a large regional reservoir and an important source for the agricultural activities well developed in the Garonne valley. The hydraulic exchange between this aquifer and the river is depending on the river’s water level. The overexploitation of water resources and the effects of climate change lead to river discharge and aquifer level to decrease over the past several years. However, this affects the economy and threaten the related ecosystems.

The Techno pole Agen-Garonne (TAG) project, green and temperate peri-urban zone, is under construction within an area of about 240 ha close to the Agen City. The project and surrounding areas, about 20 km2, is taken as a study area (Fig 1). Runoff from the TAG is collected in retention basins and used as a potential source to recharge the shallow alluvial aquifer.

In the present work, the three-dimensional (3D) groundwater model was used to evaluate the effects of the groundwater artificial recharge on the aquifer level and the maintenance of ecological low flows of the Garonne River during dry periods. The calibrated model demonstrates a good agreement between observed and simulated groundwater levels (Fig. 2).

Groundwater level measurements close to the retention basin show that the water level increases about 1 m after the rainstorm event (Fig.3). The result of the simulation illustrates that the infiltrated water, takes about 3-4 months to reach and sustain the river during low-flow summer period (Fig. 4). The relatively low temperature of inflowing groundwater into the river can be considered as an important factor to control the ecosystem function.

For better sustainable water resource management in the study area, further modelling can be performed in the context of using surface water and groundwater as a single source taking into account the agricultural and ecological needs and water scarcity.

Figure. 1