# Impact of Natural and Human Factors on Dryland Vegetation in Eurasia from 2003 to 2022
## 3 Results
### Relative Contributions of Natural and Human Factors to Vegetation Activities  
Figure 8 illustrates the spatial distribution of the relative contributions from natural factors (mean annual temperature (MAT), mean annual precipitation (MAP), soil moisture (SM), atmospheric vapor pressure deficit (VPD) and terrestrial water storage (TWS)) and human activities to the interannual variations of the normalized vegetation index (NDVI), gross primary productivity (GPP) and solar-induced chlorophyll fluorescence (SIF) during 2003-2022. We found that the impact of human activities on vegetation greening was generally greater than that of the natural factors. Overall, the relative contributions of  
Figure 7: Partial correlation coefficient between NDVI, GPP, SIF and natural factors. Red, blue and green bars represent the normalized difference vegetation index (NDVI), the gross primary productivity (GPP) and the solar-induced chlorophyll fluorescence (SIF), respectively. MAT (**a**), MAP (**b**), SM (**c**), VPD (**d**) and TWS (**e**) represent the mean annual temperature, the mean annual precipitation, the soil moisture, the vapor pressure deficit and the terrestrial water storage, respectively. WCE, EEU, the MED, WSB, ESB, WCA, ECA, TIB, EAS, ARP and SAS represent West and Central Europe, E. Europe, Mediterranean, W. Siberia, E. Siberia, W. C. Asia, E. C. Asia, Tibet Plateau, E. Asia, Arabian Peninsula and S. Asia, respectively. The symbol “**” indicates that the partial correlation coefficient has passed the significance test with \(p<0.05\). human-induced changes to NDVI, GPP and SIF were 52.45%, 55.81% and 74.18%, respectively, while the relative contributions of natural factors were 47.55%, 44.19% and 25.82%, respectively (Figure 8). At the regional scale, human activities dominated the change in NDVI in most subregions, being the highest of relative contribution in TIB (Tibet Plateau: 74.68%), followed by ECA (E. C. Asia: 61.99%) and the largest contribution from natural factors was EEU (E. Europe: 56.14%) (Figure 9). For GPP, the relative contribution of natural factors was higher than that of human activities in WCE (West and Central Europe: 56.64% vs. 43.36%) and EEU (54.56% vs. 45.44%). For ESB (E. Siberia), WCA (W. C. Asia), ECA, TIB, EAS (E. Asia) and ARP (Arabian Peninsula), the relative contribution of human activities were greater than the relative contribution of natural factors on GPP (58.78%, 60.16%, 65.97%, 81.77%, 54.03% and 70.72%, respectively). The relative contributions of natural factors and human activities to the increase in GPP were counterbalanced in the MED (Mediterranean: 49.09% vs. 50.91%), WSB (W. Siberia: 50.15% vs. 49.85%) and SAS (S. Asia: 51.43% vs. 48.57%) (Figure 9). For SIF, the contribution of human activities was higher than 62.00% in eleven sub-regions, being the highest in TIB (90.15%) during 2003-2022 (Figure 9). Further analysis of the improved (i.e., the index values show an increasing trend) regions for NDVI, GPP and SIF indicated that the total contributions of human and natural factors were 30.38%, 31.68% and 42.88%, respectively (Figure 10). In the Eurasian drylands, human activity predominated, accounting for 23.20%, 28.50% and 21.10% of NDVI-, GPP- and SIF-increased areas. Natural factors, on the other hand, dominated, constituting 15.97%, 13.09% and 2.51% of NDVI-, GPP-, SIF-increased areas. In areas where NDVI, GPP and SIF were declining, indicating vegetation degradation, the relative contributions of human and natural factors were 12.20%, 6.86% and 19.17%, respectively. Human activity predominated,  
Figure 8: Spatial distributions of the relative contributions of natural and human factors to the changes in the normalized difference vegetation index (NDVI, (**a,b**)), gross primary productivity (GPP, (**c,d**)) and solar-induced chlorophyll fluorescence (SIF, (**e,f**)). Left and right columns represent natural and human factors, respectively. accounting for 10.87%, 6.92% and 12.85% of NDVI-, GPP- and SIF-decreased areas.