Abstract: To deeply understand the sunshine duration characteristics in the ecological conservation area of West Beijing (ECAWB), China, based on the data of daily total cloud cover, low cloud cover, precipitation days, relative humidity and daily sunshine duration of Mentougou and Zhaitang National Meteorological Stations in Beijing from 1975 to 2019, the spatial and temporal variation of sunshine duration in ECAWB, as well as the correlations with the various meteorological elements, are analyzed by using climate tendency rate and Mann-Kendall test methods. The results show that from 1975 to 2019, the annual, monthly, and daily sunshine duration in ECAWB were long in western mountainous area and short in southeastern plains, with significant correlations in the daily sunshine duration between the two meteorological stations (with about 80% of the difference in the range of −2 h to 2 h). The peak of monthly average sunshine duration was observed in April and May, and the valley appeared in November and December, with a most significant decreasing trend observed in June, September and October. The seasonal distribution of sunshine duration was generally uniform, despite more sunshine duration observed in spring and less in winter. In the meantime, the annual sunshine duration during 2002–2010 were consistently below the mean value, with a greater decreasing trend observed in southeastern plains (−51.6 h·(10a)−1) than in western mountainous area (−39.5 h·(10a)−1). Anomalously higher annual and seasonal sunshine duration were mainly observed from 1980s to 1990s, while anomalously lower annual and seasonal sunshine duration mainly occurred after 2000. The sunshine duration increased significantly during 1982–1990, and then decreased considerably from 1991 to 2019. The comprehensive analysis shows that the sunshine duration in this area were negatively correlated with total cloud cover, low cloud cover, daily average humidity, and daily precipitation, while significantly positively correlated with daily wind speed as well as visibility. These findings could be critical reference for the construction and climate evaluation in ECAWB.

Key words: ecological conservation area of West Beijing, sunshine duration, spatial and temporal variation; correlations