## 3 Results and Discussion
### Agricultural Drought Year Detection  
For the identification of drought years, the 20 th percentile of the agricultural drought index was calculated, using it as the threshold below which years were considered dry years (Figure 4). As a general result, in all regions except CM, dry years were coincident in wheat and barley crops since the critical month used for drought year selection was the same for both crops. Of the three approaches applied (M, 2M and 3M) for wheat and barley, in the case of 2M, April and May were detected in all regions. Furthermore, for the three temporal approaches, very similar patterns were observed for each crop and region. Hence, the three criteria used mostly adequately identify the predominant dry years in CM and CL, as well as in BY, NS and NW. In the case of German regions, the years with agricultural drought were grouped in the last decade of study, in accordance with the soil  
Figure 3: Monthly results of SM anomaly trends (Z) and months with statistical significance \(p<0.05\) (*) in the Bayern (BY), Nordrhein-Westfalen (NW) and Niedersachsen (NS) districts. The yellow and blue blocks indicate positive and negative trends, respectively. Figure 2: Most frequent critical month and its average R, obtained from monthly and provincial correlations between SM anomalies and the annual yields of barley and wheat during the growing season in the Castilla y Léón (CL, blue) and Castilla–La Mancha (CM, orange) regions. moisture trend observed in this study and others [106]. Therefore, it could be said that the three criteria used are equally valid for the identification of agricultural drought years. In the CL region, the dry years identified (2005, 2009, 2017 and 2019) coincide for the three approaches used. In the CM region, there is variation in dry years in the three periods as well as between the two crops. Thus, the years 2005, 2012 and 2017 coincide mostly for both crops and time periods in CM. The years 2006 and 2015 were especially dry for wheat and barley crops, respectively. The drought episodes identified in CL and CM have also been detected and studied by other authors, but mostly from a meteorological drought perspective. The study [107] describes that 2005 was characterized by extremely dry conditions on the Iberian Peninsula, which had a significant impact on cereal production, decreasing it by 60% on average. The 2015 event first appeared in early spring (May and earlier) in southern France and on the Iberian Peninsula [108; 109]. Several studies have identified 2012 as a year with drought [110; 111]. Ref. [112] analyzed the drought that affected Europe from July 2016 to June 2017. They found that during that period, most  
Figure 4: Dry years detected (red bars) in each region (Castilla y Léón, CL; Castilla–La Mancha, CM; Bayern, BY; Niedersachsen, NS and Nordrhein-Westfalen, NW) for wheat (**left**) and barley (**right**) and for the three criteria (M, 2M and 3M) from 2001 to 2020.  
of Western Europe suffered a major drought event resulting in severely affected crops, especially cereals in Spain. Ref. [113] indicates that Spain suffered major droughts in 2005, 2012 and 2017. Moreover, the consequences of drought events for vegetation, such as those observed in 2015, 2018 or 2019 in most parts of Europe, are productivity losses [114]. In the German regions, a cluster of dry years was observed in the second decade of study. Almost 90% of the dry years identified in the German regions occurred from 2010 onward, with a clear incidence in 2011, 2012 and 2020, showing a clear climatic trend, which led to an increase in the frequency of droughts. These results are consistent with those obtained by the authors of [115], who reported that droughts identified in southwestern Germany from 1801 to 2018 based on meteorological indices were distributed over the study period, but in the last decade, drought episodes showed greater severity. Ref. [116] also classified the period from 2003 onward as the one with the highest incidence of severe drought events in southwestern Germany. Ref.