Abstract
Clouds are crucial components of the climate system and exert profound influences on climate processes. They play a key role in global and regional climate change, energy balance, and water cycle, and have a critical impact on precipitation and radiative transfer processes. Based on daily total cloud cover (TCC) observations from 9 stations over the Tianshan Mountains, China (TM) and 17 stations over the mountain foothills (MF) from 1970 to 2009, this study systematically assesses the spatiotemporal variability of TCC, with a focus on its long‐term trends, seasonal characteristics, and statistical associations with surface temperature (T) and relative humidity (RH). Station observations indicate that both TM and MF exhibit clear spatial and seasonal differences in TCC; however, based on the Trend‐Free Prewhitening Mann–Kendall test, neither TM nor MF exhibited a statistically significant long‐term trend in annual mean TCC during 1970–2009 (TM: 0.04% per decade,
p
= 0.81 MF: 0.24% per decade,
p
= 0.32). After removing the 8 stations with Standard Normal Homogeneity Test‐detected breakpoints within this period, the trends remained nonsignificant. The TCC based on ERA5 also showed no significant trend over TM during 1970–2009 (–0.10% per decade,
p
= 0.44), supporting the station‐based conclusion. The apparent post‐2010 increase should be interpreted cautiously because of possible observing‐system inhomogeneity. In terms of spatial distribution, station observations indicate that TCC at western TM stations is higher than at eastern TM stations, and that TCC at northern MF stations is higher than at southern MF stations. In terms of seasonal characteristics, TCC over TM exceeds that over MF in spring and summer, while the opposite occurs in winter; both TM and MF exhibit a seasonal cycle with a spring maximum and an autumn minimum. After detrending and controlling for T, TCC was significantly positively partially correlated with RH in all seasons, especially in spring, autumn, and winter (
R
> 0.6,
p
< 0.001). This study provides an observational basis for understanding the spatiotemporal variability of TCC over the Tianshan region, while highlighting the inhomogeneity‐related uncertainties in detecting long‐term climate trends from ground‐based cloud observations, as well as the potential risks of extrapolating the short‐term post‐2010 increase as a long‐term climate signal.