## 3 Method
### Crop Condition Assessment Result  
Figure 9 shows the spatial heterogeneity of crop conditions over the NCP study area for early May 2011, compared to the previous year. Figure 9a was generated from the 16-day composite MODIS NDVI data for Julian Days 153 to 168, while Figure 9b was produced from the UALR-adjusted NDVI over the same period. The color coding in the two crop condition maps is the same, except for an additional gray color in Figure 9b representing uncropped arable land. (As discussed above, pixels with a UALR larger than 0.98 in either 2010 or 2011 were excluded and are marked as this additional class in Figure 9b.) Overall, the two maps show similar spatial patterns. Generally, crop condition in the study area in early May 2011, was not as good as 2010. However, crop condition is better in 2011 compared with 2010 in central and northern parts of the study area; poorer condition crops are mostly situated in southern sections. The southernmost part of Henan province, northwest Anhui province and the peripheral areas of Jiangsu province have the worst crop conditions as a result of excessive rainfall and a lack of radiation in 2011. Better crop conditions are observed in the neighboring regions of Zhengzhou and Shijiazhuang, the capitals of Henan and Hebei provinces, respectively. Although similar overall, there are some differences in the detail between the two maps. Statistically, for the MODIS NDVI data, 8% of cropland shows a better condition (dark and light green areas) in early May 2011, compared with 2010, and 9.2% is worse (red and orange-red regions), while the rest maintained a similar condition (yellow-green areas). For the UALR-adjusted NDVI data, 13.4% of cropped land shows a better condition and 14.3% a worse condition. Crop conditions in the southern NCP are noticeably poorer in Figure 9b than that in Figure 9a. This is consistent with the UALR distribution map. Southern NCP (especially south of Henan and north of Anhui) kept more arable land uncropped during the winter crop growing season in 2010 than in 2011. In the neighboring areas of northernmost Henan province and southernmost Hebei province, crop condition was generally normal in 2011 compared with 2010 based on MODIS NDVI data (Figure 9a), while a poor crop condition is observed from the UALR-adjusted NDVI data (Figure 9b). Figure 8: The scatter plot of all valid pixels for MODIS NDVI and UALR-adjusted NDVI for early June 2011. The crop growth profiles for the study area also confirm the poorer crop condition in 2011 compared to 2010 (Figure 10). The spatial average MODIS NDVI during the winter crop growing season ranged from 0.19 to 0.66 for 2009-2010 and from 0.31 to 0.63 for 2010-2011. The corresponding UALR-adjusted NDVI ranged from 0.20 to 0.68 and from 0.32 to 0.65. The lowest NDVI occurs in winter when crops are dormant, and the peak NDVI occurs in early May when winter wheat is flowering. The peak NDVI during the 2010-2011 winter crop growing season was 4.4% lower than that during the 2009-2010 growing season, while the lowest average NDVI was much higher in 2010-2011 than in 2009-2010. The main reason was the amount of snow fall during winter in 2010-2011, which was much less than during 2009-2010. Most of the crops in the north portions of the study area during winter 2009-2010 were covered by snow, which has a much lower NDVI than dormant crops. Figure 10 shows crop growth profiles based on MODIS NDVI data (green and purple lines) and UALR-adjusted NDVI data (blue and red lines) for the NCP overall and for five separate provinces in the NCP. The provincial charts show distinctive characteristics deriving from the impact of differences in topography and climate on crop phenology and growth patterns in different regions. The overall profile for the NCP is an amalgam of these differences. For example, two sudden drops are apparent in the overall NCP 2009-2010 profiles (blue and green lines), the first in early November 2009, and the second in early February 2010.