Abstract. Groundwater recharge (GWR) is a strategic hydrologic
variable, and its estimate is necessary to implement sustainable groundwater management. This is especially true in a global warming context that highly
impacts key winter conditions in cold and humid climates. For this reason,
long-term simulations are particularly useful for understanding past changes in GWR associated with changing climatic conditions. However, GWR simulation at
the regional scale and for long-term conditions is challenging, especially
due to the limited availability of spatially distributed calibration data and due to generally short observed time series. The objective of this study is to demonstrate the relevance of using a water budget model to understand
long-term transient and regional-scale GWR in cold and humid climates where
groundwater observations are scarce. The HydroBudget model was specifically
developed for regional-scale simulations in cold and humid climate
conditions. The model uses commonly available data such as runoff curve
numbers to describe the study area, precipitation and temperature time series to run the model, and river flow rates and baseflow estimates for its
automatic calibration. A typical case study is presented for the southern
portion of the Province of Quebec (Canada, 36 000 km2). With the model
simultaneously calibrated on 51 gauging stations, the first GWR estimate for
the region was simulated between 1961 and 2017 with very little uncertainty
(≤ 10 mm/yr). The simulated water budget was divided into 41 % runoff
(444 mm/yr), 47 % evapotranspiration (501 mm/yr), and 12 % GWR
(139 mm/yr), with preferential GWR periods during spring and winter (44 %
and 32 % of the annual GWR, respectively), values that are typical of other cold and humid climates. Snowpack evolution and soil frost were shown to be
a key feature for GWR simulation in these environments. One of the
contributions of the study was to show that the model sensitivity to its
parameters was correlated with the average air temperature, with colder watersheds more sensitive to snow-related parameters than warmer watersheds.
Interestingly, the results showed that the significant increase in precipitation and temperature since the early 1960s did not lead to
significant changes in the annual GWR but resulted in increased runoff and
evapotranspiration. In contrast to previous studies of past GWR trends in
cold and humid climates, this work has shown that changes in past climatic
conditions have not yet produced significant changes in annual GWR. Because
of their relative ease of use, water budget models are a useful approach for
scientists, modelers, and stakeholders alike to understand regional-scale groundwater renewal rates in cold and humid climates, especially if they can
be easily adapted to specific study needs and environments.