Long-Term Variation Characteristics of Planetary Boundary Layer Height and Their Influencing Factors in Fuyang of Anhui Province

Rapid urbanization in Fuyang City, a densely populated city, has raised concerns about climate and environmental issues. This research focuses on understanding the long-term boundary layer structure and its relationship with meteorological conditions amid climate change. The analysis uses conventional meteorological observation data from Fuyang City, Anhui Province, high-resolution L-band sounding observations from the Fuyang sounding station between 2010 and 2019, as well as the ERA5 reanalysis data to calculate the PBLH (planetary boundary layer height) using the bulk Richardson number method. The study analyzed long-term PBLH variations in the Fuyang City, examining its relationship with meteorological factors such as 10-m wind speed, near-surface temperature, relative humidity, and surface pressure across monthly, seasonal, and interannual scales using multi-year data. It also compared observed PBLH data with ERA5 reanalysis data to identify any discrepancies. The results indicate that the PBLH at 0800 BJT (Beijing time) and 2000 BJT remains below 500 m owing to relatively weak solar radiation, leading to an underdeveloped or stable nocturnal boundary layer. The PBLH at 2000 BJT is higher than that at 0800 BJT owing to lower pressure, higher temperature, and lower relative humidity, which led to a higher uplifting of the PBLH and surpassed the effect caused by lower wind speeds. The PBLH exhibited significant seasonal variations, with the order being summer＞spring＞winter＞autumn, regardless of whether observations were taken at 0800 BJT or 2000 BJT. The ERA5-derived PBLH generally matched this seasonal variation pattern. However, there were some discrepancies: at 0800 BJT, the ERA5 PBHL was 23 m higher than observed, primarily owing to elevated wind speeds, higher temperatures, and lower atmospheric pressure in ERA5. Conversely, at 2000 BJT, the ERA5 PBLH was 99 m lower than observed, influenced by complex factors. The study found high multi-year monthly averaged correlation coefficients between ERA5 and observed PBLH, with values of 0.91 at 0800 BJT and 0.74 at 2000 BJT, suggesting ERA5’s suitability for long-term PBLH trend studies in Fuyang and southeastern regions. Both observations, and ERA5 annual average PBLH showed consistent fluctuation patterns over the years, though ERA5 indicated a slightly decreasing trend (not statistically significant at 0.05 significance level). On the monthly average scale, surface meteorological factors like atmospheric pressure and wind speed exerted a greater impact on PBLH compared to temperature and humidity. The multi-year monthly averaged PBLH from ERA5 exhibited a significant negative correlation with surface pressure and a strong positive correlation with surface wind speed. Correlations were stronger at 0800 BJT than at 2000 BJT. The annual average PBLH value did not show a significant relationship with ground meteorological elements, indicating that despite climate change increasing surface temperature and relative humidity, the change in annual average PBLH is statistically not significant. Intensive observations indicated that both observed and ERA5-derived PBLH gradually increased from 0200 BJT to 2000 BJT and then decreased, reflecting typical diurnal variation characteristics of the boundary layer height, with a deeper boundary layer during the day and a shallower boundary layer at night.