Groundwater use for agricultural production – current water budget and expected trends under climate change. Final report submitted to MAPAQ and OMAFRA

Larocque, Marie; Levison, Jana; Gagné, Sylvain et Saleem, Shoaib (2019). Groundwater use for agricultural production – current water budget and expected trends under climate change. Final report submitted to MAPAQ and OMAFRA. Montréal; Guelph, 67 p.

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Global changes from natural and anthropogenic sources (e.g. climate change, population growth, agricultural intensification) place great stress on water resources. Groundwater resources are of great importance for rural communities and for agricultural production in southern Ontario, Canada. The goal of this research was to improve the understanding of potential opportunities and challenges for the agricultural industry relying on groundwater resources in a changing climate. This was accomplished through quantifying the water budget in a water-stressed agriculturally-dominated area and examining the long-term sustainability of groundwater source availability for agriculture, considering future climate stresses and potential land use changes. In the lower portion of the Whitemans Creek subwatershed, part of the Grand River watershed, Ontario, a detailed analysis of the water budget, including collection of field data and numerical simulations using the coupled SWAT-MODFLOW model, was conducted. The water budget analysis indicates that recharge is the main component of the water cycle followed by evapotranspiration. Groundwater discharge to the stream calculated using a digital filter is between 0.34 and 1.25 m3/s with a median of 0.73 m3/s (159 and 585 mm/yr; median of 344 mm/yr). Reported groundwater use is low in the subwatershed, but allowed (permitted) amounts are close to mean annual recharge. In 2016, for example, the LWC had 47 active PTTW, pumping the aquifer (12 permits), ponds (32 permits) and surface water (3 permits) for the equivalent of 182 mm/yr. Agricultural use accounts for >95% of the permitted pumping. However, the maximum declared water use was 18 mm/yr in 2012. Modeling results from SWAT (surface model only), for the past conditions, gives a mean annual recharge of 424 mm. Simulated baseflow from SWAT for the past condition is 390 mm (0.79 m³/s) while the baseflow simulated by the SWAT-MODFLOW model is 236 mm (0.49 m³/s). This indicates the importance of the regional flow in the study area and the contribution of the recharge to the aquifer located downstream of the subwatershed. Simulations using climate change scenario data predict an increase in the annual recharge from 2000 to 2100. This increase mainly occurs during the winter months and is caused by an increase in temperature and more frequent melt events. This increase in recharge is also observed in the baseflow. In order to assess the possible impact of land use change in the water cycle, combined with climate change, four land use scenarios were tested in the SWAT model. The changes in the future water balance were masked by the large changes induced by the climate change scenarios, and thus land use change impacts were not considered with the coupled model. On average there will be more water available (recharge, stream flow, baseflow, groundwater elevation) in the subwatershed in winter and fall seasons. However, there will be changes in timing of water availability. Less water is predicated to be available during critical crop periods such as lower recharge and stream flow in spring and summer. This study has highlighted that a small subwatershed such as the LWC, with highly permeable soils, stresses on current water availability and dense agricultural activities, can be vulnerable to changes in the water budget for future conditions. It is important that predictive models are used to simulate water budgets, including future impacts of climate and land use change when possible, to ensure collective uses do not have adverse impacts.

Type: Rapport pour un gouvernement, une ONG
Mots-clés ou Sujets: Eau souterraine, rivière, interactions, agriculture, changements climatiques, SWAT, MODFLOW
Unité d'appartenance: Faculté des sciences > Département des sciences de la Terre et de l'atmosphère
Déposé par: Marie Larocque
Date de dépôt: 30 mars 2020 08:53
Dernière modification: 24 nov. 2021 14:13
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