Variations of Absorbed Photosynthetically Active Radiation over the Canadian Prairie in 2000-2008

The fraction of absorbed photosynthetically active radiation (fAPAR) determines the absorption of solar radiation by vegetation and controls the ecosystem productivity. In this paper, the fAPAR over the Canadian Prairie eco-zone (hereafter the Prairie) was estimated for 2000-2008 using the 3-D canopy radiation transfer model implemented as part of the Ecological Assimilation of Land and Climate Observations (EALCO) model and the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data. With these estimates, the fAPAR magnitude, spatial distribution, and inter-annual variations due to the impact of climate variations were investigated. It was found that the Prairie-scale average fAPAR during the peak growing season was around 0.56 during the nine study years. The inter-annual variation of fAPAR was significantly related to the climate variations over the region, with precipitation being the most important factor. The severe droughts in 2001 and 2002 over the Prairie resulted in 11.5% and 15.2% reduction respectively compared to the 9-year average fAPAR. The spatial variation of fAPAR over the Prairie was largely determined by vegetation types, growing conditions, soil types, and climate factors such as precipitation and temperature. Among the seven eco-regions in the Prairie, the fAPAR was found to be the highest in Aspen Parkland eco-region, owing to the well-growing trembling aspen, mixed tall shrubs and intermittent fescue grasslands under the conditions of favorable precipitation and fertile black soils. The fAPAR was the lowest in Mixed Grassland eco-region where about half the region was cultivated and the remainder was used for pasture or rangeland. This region had the lowest precipitation (250-350 mm per year) in the Prairie.