## 4 Discussion
### Impact of Climate Change on Ecological Change in the GGP Subregions  
Climate variability and ecological restoration programs jointly influence vegetation growth [78], thus further impacting EQ and ESs. From 2000 to 2010, the climate in the whole GGP area became warmer and wetter, with average increments of 0.0292 \({}^{\circ}\)C and 0.4685 mm per year in temperature and precipitation, respectively. Climate change showed large spatial heterogeneity, with wetter places (mainly southern subregions) becoming drier, and drier places (mainly northern subregions) becoming wetter. Most of the southern and northwestern subregions became warmer, especially in the southwest, while central and northeast subregions became colder (Figure 9). We used the slope of annual \(\text{FVC}_{\text{max}}\), \(\text{LAI}_{\text{max}}\), \(\text{NPP}_{\text{avg}}\), \(\text{WR}_{\text{pua}}\), \(\text{SWAL}_{\text{pua}}\), and \(\text{SWIL}_{\text{pua}}\) changes and the slope of annual precipitation and temperature changes to investigate the relationship between the ecological changes and climate change at a subregion scale (Figure 10). We found that the impacts of precipitation and temperature on ecological changes at a subregion level were not significant, except \(\text{WR}_{\text{pua}}\), which was impacted by precipitation very significantly (R\({}^{2}\) = 0.78, P < 0.01) (Figure 10d). Therefore, the increase in precipitation might explain the rise of \(\text{WR}_{\text{pua}}\) in most northern subregions, while the decrease led to a decline in \(\text{WR}_{\text{pua}}\) in most southern subregions. However, the \(\text{WR}_{\text{pua}}\) and precipitation of subregions did not fluctuate with the same volatility and the response of \(\text{WR}_{\text{pua}}\) to precipitation change in northern subregions was weaker than that in southern subregions, e.g., the slope values for precipitation change in the ASRNC, HGRLP, and MHRSCHH were similar, but the slopes for \(\text{WR}_{\text{pua}}\) change in the ASRNC and HGRLP were far lower than in MHRSCHH (Figure 10d). Considering the abnormal rise of annual \(\text{FVC}_{\text{max}}\), \(\text{LAI}_{\text{max}}\), and \(\text{NPP}_{\text{avg}}\) compared with climate change in northern subregions, especially in the HGRLP (Figure 10a-c), the increased forest might lead to a reduction in the water yield in arid and semi-arid regions [78; 83; 90], whereas the precipitation might become a more constraining factor to water conservation in humid areas. New planting would increase ET and induce a significant decrease in the ratio of river runoff to annual precipitation across hydrological catchments [26], and large-scale afforestation in vulnerable arid and semi-arid regions could increase the severity of water shortages [83]. Besides \(\text{WR}_{\text{pua}}\), the \(\text{SWIL}_{\text{pua}}\) in the ASMRYY and HGRLP still increased slightly under the scenarios of afforestation (Figure 10f), concurring with the discovery of [PERSON] [22], who found that planting trees in arid and semi-arid regions had failed to mitigate desertification. The correlation was relatively high between \(\text{SWAL}_{\text{pua}}\) and precipitation (Figure 10e), indicating that climate change contributes to the enhancement of SC. The fact that the effects of climate change on most ecological variables at a subregion level were not significant implied that the GGP might play a more important role in ecological change, and the difference of ecological outputs among subregions might be attributed to different regional restoration measures (Table 1). The selection and richness of tree species, area, and locations for revegetation or afforestation would significantly influence the ecological effects [91; 92]. Figure 10: Relationship between the difference in ecological changes among Grain for Green Program (GGP) subregions and climate condition from 2000 to 2010.