Irrigation expansion has kept pace with the CO2 fertilization effect on vegetation growth in a typical arid region.

Dynamics of vegetation in arid areas have drawn worldwide attention. The expansion of irrigated cropland (ICE) in arid regions contributes to increased food security and impacts on the extent and development of regional vegetation. However, the quantitative attribution of vegetation growth variation from ICE and biogeochemical factors (e.g., atmospheric CO₂ concentration, climatic factors) is still lacking. Here, we assessed key drivers of vegetation growth in the inland arid region of Northwest China (IANC) from 1982 to 2018, including ICE, increased nitrogen rates, elevated atmospheric CO₂ concentration (eCO₂) and climate drivers, using normalized difference vegetation index (NDVI) and ecosystem gross primary productivity (GPP) as measures. These variables were quantified through trend decomposition, machine learning algorithms, and a satellite-based model. The results show that vegetation growth was increased in IANC mainly due to eCO₂ and ICE. After 1995, as the regional climatic aridity intensified, the CO₂ fertilization effect on vegetation growth decreased, as the atmospheric CO₂ concentration continued to increase. Meanwhile, irrigated cropland area increased sharply, and ICE-driven GPP variation exceeded that driven by eCO₂ in the whole region, while the ICE-driven NDVI variation exceeded that due to eCO₂ when the ICE reached 6.38%. The ICE effect on regional vegetation growth rather than the CO₂ fertilization effect has mitigated the slowdown of the rate of vegetation growth caused by climate changes. Although the ICE is conducive to food security and continuous greening of arid areas, further reclamation will exacerbate water scarcity. Our results provide research base for identifying the scale of sustainable agricultural development. Highlights: Vegetation growth was enhanced in Northwest China mainly due to the CO₂ fertilization effect and irrigation expansion during 1982–2018. The effect of irrigation on vegetation growth approached or even outweighed that of elevated atmospheric CO₂ concentration after 1995. The effect of irrigation expansion mitigates the slowdown of vegetation growth trend, instead of the CO₂ fertilization effect. [ABSTRACT FROM AUTHOR]