Attenuated cooling effects with increasing water-saving irrigation: Satellite evidence from Xinjiang, China

• Published in: Agricultural and forest meteorology 2023-04, Vol.333, p.109397, Article 109397
• Main Authors: Zhang, Chao, Dong, Jinwei, Leng, Guoyong, Doughty, Russell, Zhang, Kun, Han, Songjun, Zhang, Geli, Zhang, Xuezhen, Ge, Quansheng
• Format: Article
• Language: English
• Subjects: Land surface temperature; Water use; Water-saving irrigation; Weakened cooling effect; Xinjiang
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2023.109397

•Increasing water-saving irrigation dampened irrigation cooling effect in Xinjiang.•More evident cooling effect reduction in South Xinjiang than in North Xinjiang.•Cooling effect reduction significantly correlated with declining water use.•Cooling effect reduction mainly occurred in late summer and early spring. The cooling effects of agricultural irrigation on land surface temperature (LST) are more evident in arid areas like Xinjiang Uygur Autonomous Region (Xinjiang) in northwest China. In the 21st century, irrigation practices improved, and the water-saving irrigation (WSI) area increased substantially from 1266 ha in 2000 to 2916 ha in 2019. However, it remains unclear how the cooling effects changed along with the increasing WSI area relative to traditional irrigation. Here we examine the changes in irrigation cooling effects on LST in Xinjiang from 2000 to 2020 at multi-spatiotemporal scales and analyze their relationship with irrigation water use (IWU). We find a significant decrease in daytime cooling effects (0.21 K/decade) but an increase in nighttime cooling (0.17 K/decade) over stable croplands in Xinjiang, both of which significantly (P < 0.05) correlate to the decreased IWU. Seasonally, the weakened daytime cooling effect is most evident in late summer and early spring. Spatially, the decrease in the cooling effects is much more prominent in South Xinjiang (0.48 K/decade, p < 0.05) than in North Xinjiang, possibly due to their different WSI extents, intensities, and climate conditions (e.g., precipitation). Furthermore, we identify different cooling alleviation trends in two different agricultural systems: state farms with more advanced WSI measurements and conventional farms with fewer WSI infrastructures. We find that the state farms had a higher LST (∆LST: 0.60 K) and vapor pressure deficit (∆VPD: 0.013 kPa) than conventional farms in 2000, but that gap significantly decreased to 0.32 K and 0.002 kPa in 2020 due to increasing WSI in conventional farms, suggesting that the promotion of WSI dampened the irrigation cooling effects in Xinjiang. Our findings show that WSI lessens the cooling effect of irrigation, and we suggest that WSI-related effects on temperature should be considered in climate modeling and climate change scenarios.