## 4 Discussion
Specifically, following the severe drought in 2001 ([PERSON] _et al._, 2014; [PERSON] _et al._, 2011), cropland productivity in AB and SK (Figure 7a,b) dropped to the lowest level during the observed period. Cropland productivity in these areas was continuously influenced by the drought in the following two years and then began to recover in 2004. In 2009, Canada experienced the driest year of the past 70, and comparable to the drought year of 2002 (Canada's Top Ten Weather Stories for 2009, [[https://ec.gc.ca/meteo-weather/](https://ec.gc.ca/meteo-weather/)]([https://ec.gc.ca/meteo-weather/](https://ec.gc.ca/meteo-weather/))), most cropland in central and eastern Canada was severely affected by the drought and cropland productivity in AB, SK, and MB was below the normal level of yield. In 2012, crop conditions were severely affected by a drought again and cropland productivity was below average (Canada's Top Ten Weather Stories for 2012, [[http://www.ec.gc.ca/meteo-weather/](http://www.ec.gc.ca/meteo-weather/)]([http://www.ec.gc.ca/meteo-weather/](http://www.ec.gc.ca/meteo-weather/))). Although the results from this study are encouraging, several uncertainty factors other than those investigated in this study are worth noting. The first uncertainty is from the MODIS land cover product, which has an accuracy of about 80% in identifying croplands globally [43]. SOS and EOS extracted from MODIS product may be affected by pixel mixing effect. This is inevitable when using coarse resolution MODIS products; however, the impact should be limited to the Canadian Prairies agricultural region as it is cropping intensive and major crops have roughly a similar phenology cycle. At the same time, the identification of crop SOS and EOS from remote sensing may be different from dates identified from field measurement or crop model simulation [61]. Therefore, the uncertainties in the assessment of the trend of cropland productivity and the influences of climate variables on cropland productivity in this area may also be affected by the length of growing season derived from MODIS FAPAR. It should be acknowledged that our analyses were focused solely on the influence of cumulative climatic conditions, such as cumulative daily rainfall during the growing season, on cropland productivity variation. Therefore, our study provides an annual synoptic view of the climatic impact on cropland productivity in the Canadian Prairies. In reality, cropland productivity is impacted by climatic condition in a more complex manner and finer spatial-temporal scale than that used in this study. Climatic conditions may have different impacts on the final yield at different growth stages, and the impacts may also be significantly different in different regions [3; 19; 62]. For instance, spring wheat could benefit from a slight water stress at the heading-soft dough stage in Manitoba [2], whereas canola yield in Saskatchewan could be negatively impacted by low rainfall and high temperatures at the early stage of flowering [62]. Further studies assessing the effect of climate variables on crop growth stage and final yield at finer spatial scale using remote sensing are needed.