Wang et al. (2025) Temporal Evolution and Extremes of Urban Thermal and Humidity Environments in a Tibetan Plateau City

Identification

• Journal: Land
• Year: 2025
• Date: 2025-12-29
• Authors: J. Wang, Suonam Kealdrup Tysa, G. Chen, Qiong Li
• DOI: 10.3390/land15010064

Research Groups

• State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing, China
• Department of Hydraulic Engineering, Tsinghua University, Beijing, China
• State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining, China

Short Summary

This study analyzes high-density observational data (2018–2023) from Xining, a Tibetan Plateau city, to characterize the temporal evolution and extremes of its urban thermal and humidity environments. It reveals an intensification of the urban heat island (UHI) effect and a weakening of the urban dry island (UDI) effect, with both showing increased variability and extreme events modulated by background meteorological conditions.

Objective

• To investigate the intensity, temporal distribution, variability, and extremes of summer Urban Heat Island (UHI) and Urban Dry Island (UDI) effects in Xining, a Tibetan Plateau city.
• To analyze the interaction between UHI and UDI and background meteorological conditions (temperature and humidity).

Study Configuration

• Spatial Scale: Xining City, Tibetan Plateau (36.2–36.5 °N, 101.2–102.2 °E).
• Temporal Scale: Summers (June–August) from 2018 to 2023, with hourly resolution data.

Methodology and Data

• Models used: None (observational study).
• Data sources:
  • High-density automatic weather station network (89 stations) providing hourly 2 m surface air temperature (SAT) and relative humidity (RH) data.
  • Global Artificial Impervious Areas (GAIA) dataset (2018) for urban core delineation.
  • High-accuracy digital elevation model (90 m resolution).
  • Land use/land cover data (1 km resolution) from the Resources and Environmental Science Data Platform.

Main Results

• The summer mean Urban Heat Island Intensity (UHII) in Xining averaged 1.16 °C (2018-2023), showing recent intensification from 0.89 °C in 2018 to a peak of 1.36 °C in 2021.
• The variability of daily UHII increased significantly, with the standard deviation rising from 0.30 °C in 2018 to 0.63 °C in 2022.
• The frequency of strong UHI days surged from 0–2 days during 2018–2020 to 23 days in 2022, and the maximum hourly UHII increased from 3.95 °C in 2018 to 6.60 °C in 2023.
• The summer mean Urban Dry Island Intensity (UDII) averaged 0.75 hPa (2018-2023) but exhibited a clear weakening trend, declining from 1.51 hPa in 2018 to 0.33 hPa in 2023.
• The year 2023 marked the first occurrence of "urban moist island" days (29 days with negative daily UDII, with a minimum of -0.84 hPa).
• The frequency of weak UDI days increased substantially to 14 days in 2023, while strong UDI days decreased markedly from 39 days in 2018 to 0–3 days in most subsequent years.
• Hourly UHII is significantly modulated by background meteorological conditions, showing a strong positive correlation with air temperature and a more substantial negative correlation with humidity, with humidity demonstrating greater explanatory power.
• These influences (temperature and humidity on UHII) exhibit pronounced diurnal asymmetry, being strongest at night and weak or even reversed during pre-noon hours.

Contributions

• Provides the first systematic, data-driven investigation of fine-scale (hourly) urban thermal and humidity environments and their extremes in a Tibetan Plateau city.
• Quantifies the contrasting evolution of UHI (intensifying) and UDI (weakening) in a high-altitude urban environment.
• Elucidates the differential responses of UHI to background meteorological drivers (temperature and humidity) and their pronounced diurnal asymmetry.
• Offers critical insights for urban planning and climate adaptation strategies in similar highland cities.

Funding

• Open Research Fund Program of the State Key Laboratory of Hydroscience and Engineering (sklhse-2024-C-02)

Citation

@article{Wang2025Temporal,
  author = {Wang, J. and Tysa, Suonam Kealdrup and Chen, G. and Li, Qiong},
  title = {Temporal Evolution and Extremes of Urban Thermal and Humidity Environments in a Tibetan Plateau City},
  journal = {Land},
  year = {2025},
  doi = {10.3390/land15010064},
  url = {https://doi.org/10.3390/land15010064}
}