## 4 Results  
### Drought Characteristics and Their Spatial Distribution  
We calculated the 1-, 3-, 6-, and 12-month SPEIs for Hunan Province from 1965 to 2015. Figure 4 displays the variability of the SPEI value with different time scales. Drought events had a shorter duration and higher intensity for 1-month SPEI than for 3-, 6-, and12-month SPEI. This result indicates that an increase in time scale has a smoothing effect on the intensity and duration of a single drought [7]. For 6- and 12-month SPEI, the drought event with the highest intensity occurred in October 1998 (SPEI \(6=-2.146\)) and January 2011 (SPEI 12 \(=-1.874\)), respectively. This result means that drought characteristics vary with different drought time scales. [PERSON] et al. [7] also observed this phenomenon.  
In the past five decades, drought events that lasted for 10 months mostly began in summer and winter and lasted until the winter of the following year. According to the profile of SPEI-12 (Figure 4), from 1965 to 2015, Hunan Province experienced eight drought events that lasted more than 10 months; these events began in 1970, 1977, 1984, 2004, 2006, 2008, 2010, and 2012.  
Drought duration (DD), drought severity (DS), and drought intensity (DI) were extracted from each station. A total of 7533 drought events were found throughout all stations, with an average of 85 drought events per station (accounting for 24.67-29.58%) with an average duration of 1.98 months and average severity of 2.25. Approximately, 21.6% of the stations had drought events that lasted more than 8 months; most drought events lasted less than six months. A single drought event at several stations was serious despite the weak intensity, which may be due to the shortening of the drought duration.  
The drought characteristics extracted from each station were interpolated through the kriging method to explore their spatial distribution pattern, and the results are shown in Figure 5. Figure 5e,f shows remarkable variations in the total drought events (TDE) and total drought durations (TDD), respectively, in Hunan Province during 1965-2015. TDE and TDD had almost similar spatial distribution patterns. The northern (Changde and Zhangjiajie) and southern (Yongzhou) parts of Hunan are prone to be affected by long-lasting droughts, whereas the central parts have fewer droughts.  
Average drought duration (ADD), average drought severity (ADS) and average drought intensity (ADI) are nearly uniformly distributed throughout the province, as shown in Figure 5a-c. The severity of drought in these areas ranges from moderate to severe. The north-western (Jishou and Huaihua) and central (Shaoyang and Hengyang) parts of Hunan Province constantly experience severe, long-lasting drought. However, the north-eastern region (Yiyang, Changde and Yueyang) of Hunan Province often experiences short-term drought. Amongst the areas, Loudi is the most prone to short-duration, intense drought.  
Figure 4: SPEI profiles with different time scales (SPEI\(-1\), SPEI\(-3\), SPEI\(-6\), and SPEI\(-12\)).  
The spatial distribution of maximum drought intensity (MDI) also presented certain characteristics (Figure 5d). Only the most severe drought events at each station were explored in this work. The MDI in the north,-eastern part of Hunan is relatively strong, but the drought duration here is very short possibly because the area is prone to rapid drought, but it can rapidly recover from the drought.  
Figure 6 shows the ADD, ADS, and ADI linear fits of all stations. Given that intensity is the accumulation of severity, with the extension of ADD time, drought turns to a wet state or returns to the normal state. Hence, ADD and ADS are positively correlated (R\({}^{2}\) = 0.76), but ADD and ADI are negatively correlated (R\({}^{2}\) = 0.24).  
Figure 5: Spatial distribution of drought characteristics in Hunan: (**a**) ADD, (**b**) ADS, (**c**) ADI, (**d**) MDD, (**e**) TDE, and (**f**) TDD.  
Figure 6: Correlation between (**a**) ADS and ADD and between (**b**) ADI and ADD at the meteorological stations.