Impacts of Agricultural Areas on Spatio-Temporal Variability of Daily Minimum Extreme Flows during the Transitional Seasons (Spring and Fall) in Southern Quebec

Abstract

Several statistical methods were used to analyze the spatio-temporal variability of daily minimum extreme flows (DMEF) in 17 watersheds—divided into three homogenous hydroclimatic regions of southern Quebec—during the transitional seasons (spring and fall), during the 1930–2019 period. Regarding spatial variability, there was a clear difference between the south and north shores of the St. Lawrence River, south of 47° N. DMEF were lower in the more agricultural watersheds on the south shore during transitional seasons compared to those on the north shore. A correlation analysis showed that this difference in flows was mainly due to more agricultural areas ((larger area (>20%) on the south than on the north shore (<5%)). An analysis of the long-term trend of these flows showed that the DMEF of south-shore rivers have increased significantly since the 1960s, during the fall (October to December), due to an increase in rainfall and a reduction in cultivated land, which increased the infiltration in the region. Although there was little difference between the two shores in the spring (April to June), we observed a decrease in minimum extreme flows in half (50%) of the south-shore rivers located north of 47° N.

Impact of land cover changes on Long‐Term Regional‐Scale groundwater recharge simulation in cold and humid climates

“…Destouni et al (2013) and Jaramillo et al (2013) linked historical agricultural development at the expense of grassland to increases in runoff and actual evapotranspiration in several watersheds in Sweden, thus reducing the available water for recharge. Meanwhile, increases in spring and fall minimum river flows in southern Quebec (Canada) were linked to a reduction in agriculture area in the 1950 s and were interpreted as an increase in GWR (Assani et al, 2021). Alternatively, Greenwood and Buttle (2018) showed that agricultural LC notably increased the depression‐focussed GWR compared with forested area in a complex and highly permeable moraine deposit in southern Ontario (Canada), mainly due to more intense winter soil frost, producing more snowmelt runoff that accumulated in highly permeable topographical depression, thus favouring GWR compared with agriculture area.…”

“…Others have found that land use and LC had little impact on GWR simulation, or that land use and LC impacts were smaller than those of climate change (Guerrero‐Morales et al, 2020; Mohan et al, 2018; Morgan et al, 2021; Shuler et al, 2021). These differences are most likely due to the fact that it can be challenging to distinguish the impacts of climate change from the impacts of land use and LC changes on GWR, and on all components of the water budget more generally (Assani et al, 2021; Goodbrand et al, 2022; Young et al, 2019). The study scale could also determine the importance of the impacts of land use and LC changes on GWR simulations, as local impacts of changes are not necessarily visible at larger scales (Shuler et al, 2021; Zomlot et al, 2017).…”

“…Agriculture favours topographic depression‐focussed GWR rather than the spatially distributed recharge occurring in forests due to more intense soil frost producing more snowmelt runoff that accumulates in and infiltrates from the topographic depressions (Greenwood & Buttle, 2018). Agricultural watersheds have also been shown to have lower river baseflow than forested watersheds, because runoff usually dominates in agricultural lands, thus decreasing GWR and soil water storage (Assani et al, 2021). Although local scale GWR varies with LC, it is still unclear how LC changes will impact large scale GWR in cold and humid climates within a climate change context.…”

“…Similarly,Assani et al (2021) andGoodbrand et al (2022) identified average slope and soil water storage as countering the impact of agricultural development on forested land and wood harvesting on the river flow of six watersheds of different sizes in southern Quebec (Canada) and three headwater watersheds in Alberta (Canada). While an increase in fall and spring rainfall was the second reason identified byAssani et al (2021) for the increase in minimum flow during these seasons in southern Quebec,Goodbrand et al (2022) found that climate variability also reduced impacts of land-use changes on river flow. Similarly, moister future conditions expected in southern Quebec counter balanced the decrease in GWR rates simulated using HB LC due to afforestation taking place on lowpermeability surficial deposits, thus reducing the impact of LC changes on GWR (Figure6).…”

Spatiotemporal variability of fall daily maximum flows in southern Quebec (Canada) from 1930 to 2018

“…It follows that, despite the significant increase in rainfall, part of the excess water provided by this increase was absorbed by the soil in uncropped land and reforested land. This increase in infiltration following the reduction in agricultural areas has, moreover, resulted in a significant increase in minimum flows supplied by groundwater in the fall (e.g., Assani et al, 2021Assani et al, , 2022. This increase in minimum flows was not observed on the north shore despite greater surface area of wetlands.…”