Abstract:
In order to investigate annual variations and characteristics of summer precipitation, Beijing is divided into four areas according to different land use and topographic height: The urban area (UA), suburban area (SA), north mountainous area (NMA), and south mountainous area (SMA). Results of cluster analysis based on monthly precipitation amount during 33 years verify the reasonability of the regional division. Using observed monthly rain-gauge measurements from 14 meteorological stations in Beijing, differences among four areas are investigated. Significant annual mean precipitation differences are observed among four areas, with the maximum precipitation amount observed in SA (620 mm), followed by UA and SMA, and the minimum precipitation amount observed in NMA (476 mm). In UA and SMA, the precipitation amount is similar, presenting a significant difference from SA and NMA. Precipitation amount in all the four areas shows a decreasing trend, with the highest decreasing rate observed in SA (47 mm/10 a), which passes the significance test at a significance level of 0.06, and the lowest decreasing rate observed in NMA (0.7 mm/10 a). Summer precipitation which accounts for 79.1% of the annual total amount in four areas is analyzed. Results show that UA and SMA have similar features, yet being significantly different from those in SA and NMA.Differences in precipitation between Beijing Weather Observation (BWO) and four areas are also investigated, and results show that BWO isn’t significantly different from UA and SMA in both annual and summer precipitation amount, but differences between BWO, NMA and SA are significant. Upon comparison of the statistics of root-mean-square error and correlation coefficient of precipitation between BWO and four areas, consistent results are obtained, which reveals that the representativeness of precipitation in BWO is good for UA and SMA, but is poor for NMA and SA. As a result, it suggests that some other stations should be selected in suburban and north mountainous areas to represent the characteristics of precipitation there. Together with BWO, these stations may better reflect the characteristics of precipitation variations over Beijing metropolitan area.