Groundwater level variability plays a critical role in determining the spatial and temporal distribution of water resources, driven by interactions between climate, surface water, and subsurface processes. While subsurface processes are central to the quality of water influencing groundwater-dependent ecosystems, near-surface groundwater dynamics are increasingly recognized as an impediment to urban densification, where sub-grade construction intersects the water-table and future design requires perpetual de-watering. _x000D_ Decadal-scale climate variability, combined with historic water taking practices, present challenges when attempting to isolate seasonal variability. While there exists good data to support a static long-term average water-table map, what is unclear is the magnitude of variability one should expect year to year. Using advanced fitting techniques, both the long term and seasonal trends can be isolated._x000D_ We present a regional scale (~30,000 km2) interpolated water table map superimposed with seasonal variability that can be used (in part) by municipal planners in determining areas where development can likely occur without groundwater interference. Throughout the Greater Toronto Area, seasonal shallow groundwater variability averages about ±1 m from the static mean, but in places variability can reach ±5 m. Thus, the timing of any depth to groundwater estimation is not only locally dependent, but seasonally dependent._x000D_ Seasonal trends can be visually categorized into four main distributions, each peaking roughly by season (spring, summer, fall, winter). A challenge for future work would be to isolate longer term trends from climate influences and to isolate pumping influences.
