Assessing and managing the impact of climate change on coastal groundwater resources and dependent ecosystems
Objective(s)The CLIMWAT project aimed to assess the impact of climate change on coastal groundwater resources and GDEs in three coastal systems: the Central Algarve in Portugal, the Ebre Delta in Spain and the Atlantic Sahel in Morocco. It does so by employing a set of methodologies based on climate scenarios and hydrological and hydrogeological modelling, as well as biological tools for the development of indicators of shifts that occur in GDEs. Average annual temperature is 17.2 º C in the Ebre Delta, 17.4 º C in the Central Algarve and 17.5 º C in the Sahel Atlantic, whereas mean annual rainfall corresponds to 520 mm, 660 mm and 390 mm, respectively. All areas are characterized by important aquifers exploited for irrigation and public supply and with groundwater discharges into wetlands that constitute GDEs. In the Central Algarve and the Atlantic Sahel these wetlands also receive seawater input, with well-defined fresh/saltwater transition zones.
Following the baseline characterization of the study sites, specific tasks focused on:
i. The estimate of climate change scenarios for the study areas with high spatial and temporal resolution for multiple CO2 emission scenarios and/or climate models;
ii. The application and evaluation of water balance calculations and more advanced hydrological models to estimate the impacts of climate change on surface flow and groundwater recharge for multiple scenarios, focusing on long-term trends (up to 2100) and changes to interannual and seasonal variability;
iii. The use of groundwater flow and transport models to obtain a clear picture of the evolution of groundwater levels and quality under future climate scenarios, including the movement of the fresh/saltwater transition zone in coastal zones;
iv. The assessment of structure of invertebrate communities in surface/groundwater and fresh/saltwater transition zones, so as to study their potential as bioindicators of shifts in groundwater quality and availability.
MethodologyOf the several climate scenario data sources that were considered, it was decided to use the ENSEMBLES projections, which include results from 1950 up to 2100, provide good spatial resolution (25x25 km), consider a reasonable and balanced emission scenario (A1B) and cover the three study sites of the project (for four climate models).
Data of temperature (T) and precipitation (P) were downloaded from the ENSEMBLES site. Bias correction or downscaling of the data (so that they are valid for the local conditions of the study sites) was applied using different methodologies, thereby analyzing the uncertainty of these approaches. 1960-1990 was selected as the reference period, whereas climate normal scenarios were selected for 2021-2050 and 2071-2100. The downscaled data were used to develop scenarios of surface runoff and groundwater recharge, using a variety of approaches: i) water budget calculations based on the methods of Thornthwaite-Mather and Penman-Grindley; ii) advanced hydrological models for the Spanish and Portuguese sites.
Groundwater models were developed in horizontal and vertical 2D domains. Following calibration and validation, the climate scenarios were integrated into the models, particularly focusing on three aspects: i) the evolution of aquifer recharge, ii) the evolution of irrigation needs and iii) sea level rise. Where possible, different scenarios were run in the models to analyze the sensitivity of aquifer response to the different climate model predictions, as well as the importance of each of the referred aspects.
To analyze the potential of invertebrate communities as bioindicators in GDEs, sediment samples were taken in a coastal wetland (estuary in the Central Algarve) along a gradient of increasing distance to a point of groundwater input into the estuary. The sampling design aimed to assess the community structure of sediment invertebrates in two distinct situations in terms of groundwater flow, at the end of the dry and rainy seasons, with minimum and maximum discharge, respectively. Sampling of groundwater fauna was also performed along a salinity gradient, in the Central Algarve and the Atlantic Sahel study sites.
Main results and conclusionsAll climate scenarios agree on significant increase in mean temperature (T), 1.1 to 2.6 ºC by 2031-2060 and 2.8 to 5.3 ºC by 2071-2100, with the largest rises in the Portuguese and Spanish sites, and more pronounced during late spring, summer and autumn. In the Atlantic Sahel, foreseen increases in T are more well-distributed throughout the year. Rainfall scenarios show much higher variability. For the Portuguese and Moroccan sites there is a general consensus as to the concentration of rainfall in the months of November to January. In the long-term, i.e. 2071-2100, the Portuguese and Moroccan sites are expected to see large decreases in rainfall, -12 to -40%, larger than the Ebre Delta in Spain: -7 to -13%.
Regarding recharge, scenarios indicate similar trends to that of rainfall, with less conclusive results for 2021-2050 and significant decreases in 2071-2100 in all areas: Ebre Delta (-9 to -25%), Central Algarve (-7 to -38%) and Atlantic Sahel (-38 to -48%). In the Ebre Delta, where irrigation with surface water contributes to groundwater recharge, the values vary spatially and largely depend on the presence and type of irrigation. It is also clear that crop water demand will increase, so that maintaining the current cultivated area will lead to higher irrigation needs, also because natural recharge will decrease. More efficient irrigation systems will be essential in the areas where groundwater is the main source for irrigation.
There is a high variation of estimates with climate scenario, downscaling method and recharge calculation method. This highlights the uncertainty surrounding these estimates. Notwithstanding, the mentioned trends are clear. It should be emphasized that although ENSEMBLES data only consider one CO2 emission scenario, the results can be considered relatively conservative, due to the balanced nature of scenario A1B.
Groundwater in the study area currently does not show major problems of salinization, despite the occurrence of large droughts, when groundwater discharge into the GDEs is largely reduced. A decrease in natural recharge coupled to an increase in pumping rates, mainly for irrigation, results in a twofold negative impact.
When integrating the climate scenarios into the flow and transport models, an overall decreasing trend of groundwater heads is observed, resulting in drops of 5-20 m until 2100 in the largest parts of the aquifers, though locally drops may exceed 100 m in the Ebre Delta and the Central Algarve. Lower groundwater levels will become increasingly common. This may be solved by drilling deeper wells, but this apparent solution will in fact increase the problem.
Where a fresh/saltwater interface is present, seawater intrusion is seen to occur much more frequently on a seasonal basis in the period 2071-2100, and in some scenarios throughout the entire year. In a short-term, i.e. 2021-2050 problems are less evident and uncertainty is high, particularly for the Portuguese and Spanish sites. However, this is less the case when taking into account increasing groundwater irrigation rates, as clearly shown for the Central Algarve. In the Ebre Delta, the problem is less evident, or perhaps more complex to foresee, as irrigation is mainly performed with surface water, the availability of which in future scenarios has not been studied.
The model runs for the Central Algarve show the results of incorporating uncertainty of the different recharge calculation approaches, with the results disagreeing on the extent and duration of gradient inversion that leads to saltwater intrusion. Notwithstanding, they clearly agree on the general trend of the lowering of groundwater levels and the increased occurrence of the inversion of the hydraulic gradient at the saltwater boundary, particularly in the long-term. The salt wedge will intrude several km inwards, affecting the water quality in the aquifer, impairing its use for irrigation and human consumption. Moreover, recovery in wetter years will be slow and difficult. On the other hand, the impact of sea level rise on future groundwater levels and aquifer discharge rates is seen to be negligible.
A threat that is seen to be common to the three study sites is the large reduction of groundwater discharge into the wetlands that form GDEs, particularly if groundwater withdrawals increase. Within the project framework it was possible to obtain a biological tool to monitor estuarine ecosystem response to changes in freshwater input from aquifers. Groundwater fauna sampling campaigns were conducted in the Atlantic Sahel and the Central Algarve, allowing modelling underground fauna variation with differing groundwater characteristics including salinity.
The integration of information between environmental and ecological variables was performed at different time and spatial scales between the two case studies, hence allowing a comprehensive evaluation of the dynamics of the studied GDEs. Specific taxa were identified as possible bioindicators of groundwater conditions, though due to the high endemism associated with this type of fauna, future modelling must take into consideration regional variation. It was further possible to indicate which species are likely to diminish or increase with decreased freshwater inflow, due to a combination of increased groundwater usage and climate change, hence allowing for an informed interpretation of consequences for the GDE dynamics and its influence in similar adjacent estuarine systems.
Monitoring programs based on these results are now essential for achieving success in the biodiversity conservation of these GDEs, particularly of the species identified as groundwater dependent. These programs must be sensitive to and include salinity variation of sampled locations, shown here to explain some of the groundwater and associated estuarine fauna variation. A more extensive characterization of the variation of groundwater biodiversity according to aquifer characteristics and levels of human impacts is crucial in developing proficient conservation frameworks.
The definition of sustainable yields is a difficult task due to: i) the high variability of interannual recharge characteristic of the regions; ii) the foreseen negative trends in water levels and discharge rates. Nevertheless, efforts should be targeted at guaranteeing long term sustainability of the aquifers (for water supply) as well as of the ecosystems that depend on it. The groundwater models can be used to calculate maximum annual abstraction rates that prevent the drying out of the wetlands (by guaranteeing a minimum for ecological demands), the drop of heads below a certain limit or the occurrence of seawater intrusion.
The added value of the project for the Mediterranean Scientific Community resides in the joint application of climatological, hydrological and biological data processing and modeling. In other words, the project shows how future climate scenarios and related uncertainties can be incorporated into calculations and modeling of surface water flow, groundwater recharge and groundwater flow and transport. Moreover, the project results show how certain biological communities are expected to react to future climate changes, and how they can be used as indicators of such changes.
See also article in Regional Environmental Change supplement issue (Volume 14 - Supplement 1 - Feb.2014)
Stigter T.Y., Monteiro J.P., Nunes L.M., Vieira J., Cunha M.C., Ribeiro L., Nascimento J., Lucas H. (2009). Screening of sustainable groundwater sources for integration into a regional drought-prone water supply system. Hydrology and Earth System Sciences 13: 1-15
Stigter T., Ribeiro L., Oliveira R., Samper J., Fakir Y., Monteiro J.P., Nunes J.P., Pisani B., Tavares P.C.F. (2009) Assessing and managing the impact of climate change on coastal groundwater resources and dependent ecosystems: the CLIMWAT project. International Conference on Ecohydrology and Climate Change, Tomar, Portugal, 10-12 de September, 2009
Stigter T., Ribeiro L., Oliveira R., Samper J., Fakir Y., Monteiro J.P., Nunes J.P., Pisani B., Tavares P., Fonseca L. (2010) Estudo do impacto das alterações climáticas nos recursos hídricos subterrâneos em zonas costeiras de Portugal, Espanha e Marrocos. 10º Congresso da Água, Alvor, Portugal, 22-24 March, 2010
Fakir Y., El Mandour A., Kaidrassou K., El Himer H., Stigter T., Monteiro J.P. (2010) Echanges aquifères-lagunes dans le Sahel côtier de Oualidia-Sidi Moussa (Maroc): impact sur le fonctionnement et la pérennité de l’écosystème . 2nd International Conf “Integrated Water Resources Management and Challenges of the Sustainable Development”, GIRE3D, Agadir, Morocco, 24-26 March, 2010
Shapouri M., Tavares P.C., Ribeiro L., Nascimento J., Stigter T., Monteiro J.P., Cancela da Fonseca, L. (2010) Integration of environmental and ecosystem responses to “seasonality” in surface waters and groundwater systems potentially affected by climate changes. 2nd International Conf. “Integrated Water Resources Management and Challenges of the Sustainable Development”, GIRE3D, Agadir, Morocco, 24-26 March, 2010
Stigter T., Ribeiro L., Oliveira R., Samper J., Fakir Y., Fonseca L., Monteiro J.P., Nunes J.P., Pisani B. 2010. Studying the impact of climate change on coastal aquifers and adjacent wetlands. Geophysical Research Abstracts 12: EGU2010-15399; proceedings of the EGU 2010 General Assembly, May 2010, Vienna.
Pisani B., Samper J., Ribeiro L., Fakir Y., Stigter T. (2011) El Proyecto CLIMWAT: evaluación y gestión de los impactos del cambio climático en acuíferos costeros y ecosistemas asociados. Clima y balance hídrico en la Plana de la Galera (Cataluña, España). Comunicación aceptada en: ZNS2011, Salamanca, Octubre 2011.
Li Y., Samper J., Pisani B., Ribeiro L., Fakir Y., Stigter T. (2011) El Proyecto CLIMWAT: evaluación y gestión de los impactos del cambio climático en acuíferos costeros y ecosistemas asociados. Acuífero de la Plana de la Galera y manantiales del delta del Ebro (Cataluña, España). Comunicación aceptada en: ZNS2011, Salamanca, Octubre 2011.
Silva A.C.F., Tavares P., Shapouri M., Stigter T.Y., Monteiro J.P., Machado M., Cancela da Fonseca L., Ribeiro L. (in submission) Estuarine biodiversity as an indicator of climate change effects on groundwater discharge. Estuarine, Coastal and Shelf Science Journal ii
El Himer H., Fakir Y., El Mandour A., Lepage M., Stigter T.Y., Ribeiro, L. (in progress) Hydrogeological approach developed in CLIMWAT project for vulnerability assessment of the Ramsar wetland of Oualidia-Sidi Moussa, Atlantic coast, Morocco
Fakir Y., El Himer H., Lepage M., Stigter T.Y., Ribeiro L., Monteiro, J.P., Nunes J.P. (in progress) Assessing the impact of climate change on the coastal groundwater resources of the Sahel of Oualidia and Sidi-Moussa, Morocco: hydrogeological modeling
Tibor Stigter, Geo-Systems Centre/CVRM, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal, [email protected]
CLIMWAT Kick off meetingAddress: Lisbon
Date: 05 March 2009 / 06 March 2009
CLIMWAT Mid Term WorkshopWorkshop - Assessing and managing the imapct of climate change on water resources in coastal wetlands
Address: Marrakech, Morocco
Contact: [email protected]
Date: 29 March 2010 / 30 March 2010
Address: StMiguel, Azores, Portugal
Date: 21 June 2010 / 25 June 2010
- CLIMWAT_Nov2008: Powerpoint CIRCLE MED Kickoff, Rome Nov.2008
- CLIMWAT Poster 09/2009: Poster at CIRCLE Final Conf. in Vienna
- CLIMWAT Final Report - Executive Summary : Part A executive summary
- CLIMWAT Final Report - Cover, objectifs and references : CLIMWAT objectives and references
- CLIMWAT Final Report - work package 1: CLIMWAT project final report part B work package 1 - Baseline Characterization and Selection of Monitoring Locations - February 2011
- CLIMWAT Final Report - Work Package 2: CLIMWAT - Work Package 2 - Predicting the Impact of Climate Change on Surface and Groundwater Resources (February 2011)
- CLIMWAT Final Report - Work Package 3: CLIMWAT - Work Package 3 Groundwater Monitoring and Modelling February 2011
- CLIMWAT Final Report - Work Package 4: CLIMWAT - work package 4 - Application of Bioindicators to Monitor the Ecotones February 2011
- CLIMWAT Final Report - Coordination: CLIMWAT Final Report - part C - Coordination
- CLIMWAT Final Report - Publications: publications
- Final Conference Climwat presentation: 22-23 Mars 2011, Aix-en-Provence
- Changement Climatique et littoral méditerranéen: comprendre les impacts, construire l'adaptation: Synthèse des programmes de recherche Circle-Med
- Climate Change and Mediterranean Coastal Areas: Understanding the Impacts and Developing Adaptation Strategies: An overview of the CIRCLE-Med Research Projects, 2008-2011