## 3 Results
### Responses of Sugarcane Greenness and Photosynthesis to the 2009 Drought  
To investigate the different responses of sugarcane greenness and photosynthesis to the 2009 drought event, we compare seasonal variations in the 16-day mean and multiyear mean and change percent of the EVI and SIF from July to November 2009 over the entire study area (Figure 8). During the early stage of the 2009 drought (as shown in Figure 4a), SIF showed a quick negative response with a reduction of approximately 2.5% from the multiyear mean to the drought on DOY 241 (which corresponds with the second half of August). However, the EVI did not show a negative response during this period, and, thus,  
Figure 7: Spatial distributions of monthly LST and ET anomalies from July to November 2009. (**a,b**) are anomalies from the multiyear mean, and (**c,d**) are standardized anomalies from the multiyear mean.  
is not able to capture the early stage of drought stress. When the study area suffered from extreme drought stress in September 2009 (as shown in Figure 4a), the EVI just started to show a negative response to drought on DOY 273 (which corresponds with the second half of September), which was 32 days later than the SIF response. During the same period, SIF declined \(-19.7\%\) from the multiyear mean, which is much larger than the decreased magnitude of the EVI (\(-4.8\%\)). Under continuous drought stress, SIF and the EVI decreased significantly compared with the multiyear mean, but the decreased magnitude of SIF was always much larger than that of the EVI until November 2009. These results indicate that SIF can closely capture the temporal dynamics of drought on sugarcane, and is much more sensitive to drought stress than the EVI in terms of both the time and magnitude of response.  
To deeply explore the spatial dynamics of the response of sugarcane greenness and photosynthesis to drought stress, we analyzed the spatial distributions of monthly EVI and SIF anomalies (Figure 9), and the monthly area percentage of drought-induced sugarcane losses indicated by the EVI and SIF (Figure 10) from July to November 2009. In July and August 2009, both the EVI and SIF did not show negative anomalies in a large area. In September, approximately 60.8% of the study area, mainly located in the central and eastern parts, suffered from slight losses indicated by SIF, 17.5% suffered from moderate losses and 9.8% suffered from severe losses. However, only approximately 12.5% of the area, located in the central parts, was affected by slight losses observed by the EVI in September. Then, SIF declined from the multiyear mean in almost the entire study area in October, and the area percentages for slight, moderate, severe, and extreme losses are 90.9%, 76.2%, 53.8%, and 27.9%, respectively. During the same period, approximately 46.1% of the area, mainly  
Figure 8: Seasonal variations in the 16-day mean and multiyear mean (**a**) EVI and (**b**) EVI change percent, (**c**) SIF and (**d**) SIF change percent from July to November 2009 over the entire study area.  
located in the central parts, suffered from slight losses indicated by the EVI, but the EVI is not able to capture the extreme losses. Compared with SIF, the EVI still underestimated sugarcane losses in terms of both area and severity in November. During this drought event, the EVI could only capture the sugarcane losses mainly in the central parts, which were the drought center from September to November 2009. In particular, the regions of extreme losses indicated by SIF were located in most parts of the study area during October and November, which coincides with the regions affected by extreme drought stress (as shown in Figure 5a). Overall, SIF can closely capture the spatial and temporal dynamics of drought stress on sugarcane during the 2009 drought.  
Figure 9: Spatial distributions of monthly EVI and SIF anomalies from July to November 2009. (**a**,**b**) are anomalies from the multiyear mean, and (**c**,**d**) are standardized anomalies from the multiyear mean.