## 3 Results
### Impacts of Drought on Forest Ecosystem Measures of NPP, ET and WUE  
Mean annual baseline conditions and drought conditions of NPP, ET and WUE by three drought classes (D1: moderate drought, D2: severe drought and D3: extreme drought) was calculated in Table 1. The results indicated that the NPP and ET under normal conditions and drought conditions in severe drought regions were all larger than that in the other two drought classes. Thereby, WUE under baseline conditions and drought conditions were highest in the extreme drought region, followed by the severe drought region. Based on one-way Analysis of Variance (ANOVA), significant differences of NPP (\(p<0.0001\)), ET (\(p<0.0001\)) and WUE (\(p<0.0001\)) can be found between drought classes (Table 1). The spatial distributions of baseline NPP, ET and WUE vs. NPP, ET and WUE under the drought condition (i.e., 2009 and 2010) were compared in Figure 5. Annual NPP in 2010 showed a pattern of lower than normal values in almost 61% of forest area in south-western China (Figure 5e). The highest reduction of NPP in a drought period (2009 and 2010) was found in the central part of Yunnan province, with an annual reduction of 100 gC/m\({}^{2}\) (Figure 5d,e). The highest increment of ET in a drought period (2009 and 2010) was mainly found in south-west and north-west parts of the study region (Figure 5i,j). The ratios of forest area in 2009 and 2010 that exhibited declines in ET under drought conditions are 73% and 59%, respectively. In 2009, just 30% of forest area showed an increasing  
Figure 4: The inner-annual variation of soil moisture derived from microwave information during 2006–2010 in south-western China. The soil moisture in two drought years was separately compared to the baseline conditions (2006–2008). trend in WUE under drought conditions. However, the ratio of forest area in 2010 that exhibited an increment in WUE under drought conditions increased to 54%. In the D1 region (Moderate drought), NPP and ET in 2009 declined by 78 gC/m\({}^{2}\)/yr. and 28 mm/yr related to baseline values. In the D2 region (severe drought), NPP and ET in 2009 declined by 75 gC/m\({}^{2}\)/yr. and 14 mm/yr related to baseline values (Table 1, Figure 5). Furthermore, the reduction of NPP and ET in 2009 compared to baseline values was similar to that in the D1 region, with the values of 74 gC/m\({}^{2}\)/yr and 22 mm/yr. The annual WUE in 2009 in three drought classes was a little higher than in the baseline condition (Table 1, Figure 5). In 2010, the changes in NPP and ET in each drought class were not obvious (Table 1, Figure 5). The annual WUE in 2010 was a little higher than that in 2009 for each drought class. The time series of NPP, ET, and WUE under the normal condition and the drought condition were extracted by drought class (Figure 6). The seasonal pattern of NPP and ET showed a single peak for both baseline and drought conditions. The baseline NPP and NPP under drought conditions in the moderate drought region exhibited no differences in the second half of the drought period (Sep. 2009 to March 2010) (Figure 6a). Meanwhile, no differences could be found between ET under normal and drought conditions in the moderate drought region during the drought period (Figure 6d). In the severe drought region, NPP and ET under drought conditions during the drought period showed smaller values than that under normal conditions. The fact that drought directly reduced the NPP and ET during drought periods can also be found in the extreme drought region. The seasonal pattern of WUE under normal and drought conditions showed the lowest values in summer. In the first half of the drought period, WUE under the drought condition was obviously smaller than that under normal conditions in moderate and severe drought-class regions. But in the beginning of 2010, WUE under drought conditions exceeded the WUE values under normal conditions in these two drought-class regions.