Long-term Trends of Precipitable Water Vapor and Temperature at the Delingha Observatory

Long-term variations in precipitable water vapor (PWV) and temperature are critical for ground-based astronomical observations at infrared, millimeter, and sub-millimeter wavelengths. This study presents a comprehensive 40 yr analysis (1984–2023) of atmospheric conditions at the Delingha Observatory on the northeastern Tibetan Plateau, based on ERA5 reanalysis and in situ measurements. The site exhibits a median PWV of 3.96 mm, with PWV remaining below 6.00 mm for approximately 63% of the time. The median temperature is 2.32°C, with a median nighttime variation amplitude of 11.97°C. Both PWV and temperature exhibit strong seasonal cycles, with highest values typically observed in summer (peaking in July) and lowest in winter (January). Statistically significant long-term trends are observed, with annual mean PWV increasing by +0.24 mm decade −1 and temperature rising by +0.42°C decade −1 . Furthermore, the observed correlations suggest that PWV is significantly modulated by the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO), while temperature also shows significant correlations with the El Niño-outhern Oscillation, in addition to the NAO and PDO, with phase lags ranging from 0 to 11 months. These findings highlight the importance of incorporating climate diagnostics into long-term planning for telescope scheduling and site management.