## 3 Results
### Spatial Patterns of Cropland Productivity and Climate Indices  
As discussed above, CFAPAR\({}_{\text{CAR}}\) was used as a surrogate for cropland productivity to assess the variation of cropland productivity during 2000-2013. The spatial patterns of average annual CFAPAR from 2000 to 2013 on the Canadian Prairies are shown in Figure 3. In general, the spatial patterns of CFAPAR were in conformity with the distributions of agro-climatic zones (Figure 1b). The average annual CFAPAR in the sub-humid region is the highest among the three agro-climatic zones (-75), followed by the semi-arid region (-56) and the arid region (-50) (Figure 3). At the provincial level, MB had the highest CFAPAR (-85) among the three provinces, followed by AB (-80) and SK (-65).  
The spatial distributions of climate indices, including cumulative rainfall, daily mean temperature and cumulative daily radiation during a growing season, are shown in Figure 4. In general, their spatial distribution patterns are consistent with the distribution of agro-climatic zones. The growing season cumulative rainfall in the prairie region was generally less than 450 mm (Figure 4a), and decreases  
Figure 3: Spatial distribution of the average annual cumulative FAPAR (CFAPAR) during 2000–2013.  
Figure 2: Correlation between the cropland Net Primary Production at the CAR level (NPP\({}_{\text{CAR}}\)) derived from crop (barely, wheat, canola and oats) yield reports of Statistics Canada and cumulative FAPAR at CAR level (CFAPAR\({}_{\text{CAR}}\)).  
from the sub-humid area to the arid area. The sub-humid area received the highest amount of rainfall in each growing season (~273 mm), especially in the area along the western and eastern borders of the region (>350 mm). The cumulative rainfall was higher in the semi-arid area (~205 mm) than in the arid zone (~183 mm). The growing season mean temperature generally decreased from the sub-humid to the arid region (Figure 4b). The pattern of temperature distribution in the sub-humid region was more complex than in the other two regions as the temperature in AB was lower than that in SK and MB. The cumulative radiation during a growing season showed an opposite order of distribution compared with that of daily average temperature (Figure 4c). The highest value of radiation occurred in the western portion of the sub-humid region in the province of AB.  
By comparing the spatial patterns of cropland productivity in Figure 3 and climate indices in Figure 4, we observed that the spatial patterns of the climate variables over the growing season were very similar to that of cropland productivity. One of the factors that contributed to these spatial patterns was the duration of the growing season length, which was determined by SOS and EOS, as discussed by [PERSON] _et al._ (2014). The overall correlation between average annual CFAPAR and climate variables are shown in Figure 5. Both cumulative rainfall (\(r\) = 0.79, \(p\) < 0.01) and cumulative radiation (\(r\) = 0.76, \(p\) < 0.01) were positively correlated to cropland productivity, while the growing season mean temperature showed a negative relationship (\(r\) = \(-\)0.73, \(p\) < 0.01) with cropland productivity. Partial correlation analysis (Table 1) demonstrated that spatial patterns of the annual CFAPAR was mostly affected by the cumulative rainfall (\(r\) = 0.60, \(p\) < 0.01) and the growing season mean temperature (\(r\) = \(-\)0.46, \(p\) < 0.05), and not by cumulative radiation (\(r\) = 0.00, \(p\) > 0.1).  
Figure 4: Spatial distribution of climate indices during crop growing seasons from 2000 to 2013 for cumulative rainfall (mm) (**a**); growing season mean temperature (\({}^{\circ}\)C) (**b**); and cumulative short wave radiation (MJ\(\cdot\) m\({}^{-2}\)) (**c**), respectively.