Observed Hydroclimatic Trends and Their Implications Over Water-Cycle Dynamics in Montérégie, Southern Quebec, Canada.

A comprehensive understanding of groundwater recharge processes is essential for sustainable water resource management under climate change and increasing anthropogenic pressures. This study evaluates hydroclimatic trends (1980-2023) and their impacts on water-cycle dynamics in Montérégie, a predominantly agricultural and forested region in southern Quebec, Canada, characterized by spring snowmelt and biannual baseflow discharge. Historical records of temperature, precipitation, streamflow, groundwater levels, and land cover are analyzed for 20 subwatersheds and 50 piezometers, with missing data addressed using Multiple Imputation by Chained Equations. Trends are assessed using Mann-Kendall and Sen's Slope tests, while potential groundwater recharge is simulated with the GR4J hydrological model coupled with the CemaNeige snow module. Results indicate significant regional warming, particularly in summer and autumn, leading to longer growing seasons and more frequent winter melt events. Precipitation intensity has increased, contributing to slightly higher winter streamflow. Approximately 75% of annual GR4J percolation occurs during winter-spring. Recharge increases in the Baie Missisquoi due to earlier snowmelt but declines elsewhere because of higher evapotranspiration and drier soils. Groundwater levels rise in central Richelieu but decline in central-western Montérégie due to pumping and limited recharge capacity. These findings support adaptive groundwater management.