Emerging evidence demonstrates that nocturnal sap flow (Qn) is a nonnegligible component among many tree species, and depends on the climate and water conditions. We investigated Qn dynamics for Populus popularis, a main tree species in China's farmland shelterbelts, in arid climate and shallow groundwater environments. Tree water use of the P. popularis stand was quantified using sap flow measurements during the growing seasons of 2018-2021. Leaf area index (LAI), nighttime vapor pressure deficit (VPDn), nighttime wind speed at 2 m height (u2n), soil water content in the 0-30 cm soil layer (SWC0-30 cm), and groundwater table depth (GTD) were involved in this study. Results indicated that mean daily Qn and daily proportion of Qn to sap flow were 0.11-0.26 kg m-2 d-1 and 6 %-9 % in four years, respectively. The mean daily proportion of Qn to sap flow was higher in May and September than in other months. Compared with clear nights under similar VPDn and GTD conditions, rainy nights prompted a significant increase in normalized nocturnal sap flow (Qn/LAI, derived by dividing Qn by LAI) after midnight as stem refilling accelerated. SWC0-30 cm and GTD were the primary factors determining Qn/LAI. Qn/LAI could be depressed by VPDn under low SWC0-30 cm. Rising u2n promoted slightly Qn/ LAI over four years. The increase in GTD induced a reduction in daytime sap flow, thereby elevating Qn/LAI over four years, except for 2018. Qn in P. popularis stand could be used for stem water recharge under physiological regulation. Our results reveal species-specific water use strategies, thereby understanding nocturnal water uptake of plantations and refining silvicultural techniques in similar climatic zones worldwide.