## 5 Discussion
### Comparison of EVI Anomalies with Weather Data and Crop Yields
#### 5.2.2 EVI Deviances and Their Drivers in Other Years  
Apart from 2003 and 2018, we could depict the following years standing out with negative EVI anomalies or below-average yields: 2006, 2007, 2010, 2011, and 2013.  
The year 2006 reached low yields in maize and potatoes and was characterized by varying weather conditions throughout the year. July 2006 reached the highest temperatures ever recorded at that time [41; 42]. At the same time, in total, precipitation amounts were relatively normal, and in particular, a wet August prevented large damages due to the heatwave [41]. However, winter 2005/2006 lasted relatively long with cold temperatures until the second half of March [41]. This is in accordance with the EVI anomaly pattern of 2006 of this study, showing relatively negative conditions for the vegetation at the beginning of the vegetation period, but with below-average temperatures being the limiting factor at the time. Both the heatwave and the long-lasting winter might have reduced yields in 2006.  
Crop statistics of 2007 show yields below-average for winter wheat and for rye and winter cereal. March and April 2007 were relatively warm and dry, May 2007 was very wet [43]. The EVI signal shows positive effects in March 2007, which are probably a result of the warm conditions in the phase of phenological onset. The vegetation stress level seems to be minimized through the wet May [43]. However, reduced harvests in cereal might have occurred as, due to the spring drought, a reduced number of ears were developed [44]. Such a small-scale effect is not visible in the EVI anomaly pattern. Another known drought year occurring majorly in Eastern Europe/Eurasia was 2010 [10], which is also visible within the time series showing negative vegetation condition.  
The year 2011 shows strong negative values in particular in the EVI anomalies for cropland. The EVI deviances (Figure 5) reveal negative effects in the first half of the year with June being the most affected month, the second half is positive. The crop yield statistics also show below-average harvests, but only for rye and winter cereal. It can be assumed that these effects were caused be unfavorable cultivation conditions (wet and cold) in winter 2010/2011 [45], which lead to recorded damages of winter cereal. In addition to that, relatively dry conditions in western parts of Germany in spring (especially in May) had some negative influence on the cultivation of field crops [45].  
We also found negative effects in EVI in April 2013. The reason for that are most probably also not dry or hot weather conditions, but a long-lasting winter and a late phenological onset as in large parts of Germany the snow cover was present until the second half of April [46]. This effect is also discernable in silage maize and--a little less prominently--in potato yields, but not in the winter cereals, highlighting the varying impacts of different abnormal weather conditions on different crop types.  
Another notable year is 2015, as it was also dry and hot, especially in central and southern Germany [47]. However, within this study, no negative conditions for the vegetation were found considering the area of Germany. From a hydrological perspective, the drought was moderate and covered a smaller extent compared to 2003 [39]. Even if the meteorological situation was not so different from 2003 in some regions, water surplus from the preceding winter and spring 2015 prevented a hydrological drought [39]. This would explain the average EVI signal in 2015. This is also in accordance to the harvest statistics as none of the four investigated crops showed a yield below one standard deviation from the mean in 2015 at least averaged over Germany.