Objective Urumqi is located in a typical arid region, where urban tree growth is highly susceptible to water deficit, high temperature, atmospheric drought, and related environmental stresses. To clarify the intra-annual radial growth dynamics of Ulmus pumila, a dominant urban tree species in arid regions, and its relationship with meteorological factors, this study investigated the radial growth patterns of U. pumila at daily and seasonal scales and identified the major meteorological drivers. The results are expected to provide a scientific basis for urban greening management and ecological planning in arid regions.

Method High-precision radius dendrometers were used to monitor the radial growth of four U. pumila in urban Urumqi over three consecutive years from 2019 to 2021. Diurnal variation and seasonal dynamics of radial growth were analyzed. We used key meteorological data from a nearby weather station. The data included air temperature, precipitation, vapor pressure deficit, and soil temperature at different soil depths. We applied five analytical methods: the maximum value method, temperature threshold method, Gompertz growth model, Pearson correlation analysis, and sliding correlation analysis. These methods were used to determine the start and end dates of the Ulmus pumila growing season, as well as the date of peak growth rate. We also calculated the average growth rate at growth onset, and identified the main meteorological factors affecting radial growth.

Result (1) The growing season of Ulmus pumila in Urumqi lasted from early April to early November (approximately DOY 103–308). The peak growth rate occurred in mid-May (approximately DOY 135). The average growth rate at growth onset was 10 µm/d. (2) Radial growth mainly occurred at night, approximately from 21:00 to 03:00, and reached its daily peak at around 02:00, indicating distinct diurnal rhythmicity and seasonal periodicity. (3) Correlation analysis showed that the radial growth of Ulmus pumila was significantly and positively correlated with precipitation and relative humidity, whereas it was significantly and negatively correlated with vapor pressure deficit and sunshine duration, indicating that water availability was the primary factor limiting its radial growth. Moving correlation analysis further revealed that radial growth during the early growing season was mainly driven by air temperature and soil temperature, and gradually shifted to be dominated by precipitation and relative humidity from mid-summer through autumn.

Conclusion The radial growth of U. pumila in Urumqi showed a pronounced daily rhythm of daytime contraction and nighttime expansion, as well as stable seasonal periodicity. Its growth response exhibited a seasonal transition from thermal regulation in the early growing season to water limitation in the middle and late growing season. The date on which soil temperature at a depth of 20 cm remained above 12.5 ℃ provided a reliable indicator of growing-season onset. These findings offer quantitative support for phenological forecasting, precision irrigation, urban green-space management, and the maintenance of urban forest ecosystem functions in arid regions.