From river flow regime diversity to proxies for hydrologic homogeneity a Canada-wide case study.

Zonal classifications, such as those based on biomes and ecozones, are commonly used to contextualize short-term dynamics and long-term environmental change. One challenge in hydrology is the lack of zonal classifications that explicitly incorporate flow statistics. To date, few studies have evaluated whether non-hydrological zonal classifications can serve as proxies for flow dynamics across large, heterogenous regions. Taking Canada as an example, the focus was on 2531 hydrometric stations for which select streamflow signatures were computed. Those signatures, coupled with catchment characteristics, were used to distinguish flow regimes based on their degree of temporal variability-categorizing them as erratic or persistent-and their main water sources-either shallow subsurface flow or groundwater. Results show that catchments with higher cropland and urban cover and higher percentages of clay soils were associated with erratic regimes fed by shallow subsurface flow. Conversely, catchments with higher forest and semi-permanent water features were associated with persistent regimes. The high degree of intra-region and inter-region hydrologic heterogeneity was typically not well captured by non-hydrological zonal classifications. Caution is therefore warranted when using existing non-hydrological zonal classifications for regional water policy planning, as they may lead to a mischaracterization of spatial differences in streamflow patterns.