# Forest Resistance and Resilience to 2002 Drought in Northern China
## 3 Results  
### Spatio-Temporal Characteristics of Droughts  
The time series of mean growing season SPEI 12 (Figure 2a) illustrated the overall drought condition from 1902 to 2015 for the stable forests. During the 114 years, forests in northern China experienced ten extreme drought events, which happened approximately once per decade. There were four of these extensive drought events occurred after year 2001, which were in 2002, 2003, 2007, and 2008. Despite the drought events in 2003 and 2003, forests were generally under normal water condition during 2004 to 2006. However, after the extreme and pervasive drought in 2007 and 2008, our study objects experienced dramatic fluctuations from moderate drought (2009) to moderate wet (2010), which might cause an even more complicated situation for comparing the ecosystem stability. Thus, we decided to focus on exploring the resistance and one-to-four-year resilience of forests to drought in 2002. The involved time period is 2001-2016.  
To classify the drought condition spatially, we retrieved the minimum SPEI12 during growing season in 2002 for each forest pixel. Unsurprisingly, most of the forests in northern China experienced drought under different levels in 2002 (Figure 2b). There were 97.37% of the forest pixels had a SPEI12 value lower than zero, in which 53.00% were under severe droughts (\(-2<\text{SPEI12}\leq-1.5\)), and 23.65% experienced extreme droughts (\(\text{SPEI12}\leq-2\)). The severe and extreme drought regions were clustered in the northeast and east of northern China, which were covered with dense forests. Only 18.62% of the forest pixels were under moderate drought condition (\(-1.5<\text{SPEI12}\leq-1\)). The result suggested that large areas of the forests in northern China experienced severe-to-extreme droughts in 2002.  
To compare the areas of the DNF and DBF under drought, we counted the ratio of DNF and DBF pixels under vary water condition separately. The majority of the DNFs experienced drought events, in which 31.45% encountered extreme drought, and 68.42% were under moderate drought in growing season in 2002. Only 0.13% of the DNFs were under normal to wet conditions. To the DBF pixels, 59.33% experienced extreme drought, 24.81% were under moderate drought, and 15.69% were under normal to wet conditions, respectively (Figure 3). Since drought events occurred extensively among our study objects, pixels under drought events in 2002 were selected for analyzing.  
Figure 2: Spatial and temporal characteristics of SPEI12: (**a**) The time series of mean growing season (April to October) SPEI 12 during 1902–2015 (blue line) and the overall percentiles of the stable pixels (solid red lines for 10 th and 90 th percentile, which stands for extreme drought and extreme wet event thresholds; dashed red lines for the 25 th and 75 th percentile, which stands for moderate drought and moderate wet even thresholds; and the gray-colored range marked the SPEI values of normal years); (**b**) the spatial distribution of water-balance condition in 2002 for the stable forest pixels, the climate events were classified with individual SPEI12 thresholds calculated from the 1902–2015 records of each pixels respectively.