Runoff and Climate Change at the Field-Scale: Comparing Projections and Observations Across Regions

Abstract:

Water quality is a globally significant issue that is tied to land use and geomorphic conditions as well as climate drivers as excess nutrients are transported hydrologically. An intensification of the hydrologic cycle is predicted in future; however, not all regions will respond in the same way and cold regions where snowmelt and frozen ground may play a role in hydrology are expected to be strongly impacted by warming. This study explores the impacts of climate and hydrometeorology (winter severity, antecedent conditions, precipitation form, event characteristics) on runoff at the agricultural field scale from field sites located in both the cold, sub-humid Canadian Prairies and cool, humid southern Ontario, Canada. We used a robust dataset of edge-of-field surface runoff and tile drainage hydrographs of almost 500 events across eight agricultural fields with varying soil textures (clay, silt loam, clay loam), including both snowmelt and rainfall runoff responses. The two broad regions have vastly different climates, where the Canadian Prairie sites have more severe winters and frozen ground in winter, contrasted by dry summers with periodic intense rainfall from convective storms, and the southern Ontario sites have less severe winters with greater snow cover and minimal ground frost, and more humid summers subject to large, persistent frontal precipitation systems. On an annual scale, these differences produce vastly different hydrological budgets. However, hydrograph analysis demonstrated that individual edge-of-field runoff events in the two regions had similar magnitudes and volumes. A suite of flashiness metrics suggests that Canadian Prairies had significantly flashier small-scale hydrology, with hydrographs with wider range, sharper peaks, steep slopes, and more noise, and these differences persisted across event and annual scales. Significant baseflow and the presence of tile drainage only played significant roles in end-of-field hydrology in southern Ontario. However, the impacts of tile drainage may become more important in future warmer and wetter climates with less frozen ground in the Canadian Prairies. This work provides an improved understanding of how runoff dynamics may respond to a range of climate drivers, and the potential impacts on agricultural water quality are discussed.