Simulating the hydrological impacts of land use conversion from annual crop to perennial forage in the Canadian Prairies using the Cold Regions Hydrological Modelling platform

[摘要] The Red River is one of the largest contributing sourcesof discharge and nutrients to the world's 10th largest freshwater lake,Lake Winnipeg. Conversion of large areas of annual cropland toperennial forage has been proposed as a strategy to reduce both floodingand nutrient export to Lake Winnipeg. Such reductions could occur either via a reduction in the concentration of nutrients in runoff or through changes inthe basin-scale hydrology, resulting in a lower water yield and the concomitantexport of nutrients. This study assessed the latter mechanism by using thephysically based Cold Regions Hydrological Modelling platform to examine thehydrological impacts of land use conversion from annual crops to perennialforage in a subbasin of the La Salle River basin in Canada. This basin is a typicalagricultural subbasin in the Red River Valley, characterised by flattopography, clay soils, and a cold subhumid, continental climate. Long-termsimulations (1992–2013) of the major components of water balance werecompared between canola and smooth bromegrass, representing a conversionfrom annual cropping systems to perennial forage. An uncertainty frameworkwas used to represent a range of fall soil saturation status (0 % to 70 %),which governs the infiltration to frozen soil in the subsequent spring. The modelsimulations indicated that, on average, there was a 36.5  ±  6.6 %(36.5  ±  7.2 mm) reduction in annual cumulative discharge and a29.9  ±  16.3 % (2.6  ±  1.6 m 3  s −1 ) reduction in annualpeak discharge due to forage conversion over the assessed period. Thesereductions were driven by reduced overland flow 52.9  ±  12.8 %(28.8  ±  10.1 mm), increased peak snowpack (8.1  ±  1.5 %,7.8  ±  1.6 mm), and enhanced infiltration to frozen soils (66.7  ±  7.7 %, 141.5  ±  15.2 mm). Higher cumulative evapotranspiration (ET)from perennial forage (34.5  ±  0.9 %, 94.1  ±  2.5 mm) was alsopredicted by the simulations. Overall, daily soil moisture under perennialforage was 18.0 % (57.2  ±  1.2 mm) higher than that of crop simulation,likely due to the higher snow water equivalent (SWE) and enhancedinfiltration. However, the impact of forage conversion on daily soilmoisture varied interannually. Soil moisture under perennial forage standscould be either higher or lower than that of annual crops, depending onantecedent spring snowmelt infiltration volumes.

[学科分类] 妇产科学