The Regionalization and Temporal Characteristic of Rainfall Anomalies in North China During Summer

North China is one of the three rainfall areas in eastern China. Precipitation over North China shows the characteristics of burstiness and locality. According to the statistics, 80%—90% precipitation occurs from June to August. Sometimes daily precipitation of a rainstorm can be up to 50% precipitation amount of that month. So it is important to forecast precipitation correctly especially to forecast larger magnitude precipitation correctly.Objective precipitation forecast is a difficult problem in NWP products interpretation at present in which models are always established station by station. Precipitation especially larger magnitude precipitation is small probability event for individual station, so establishing an effective forecast equation is difficult. Precipitation intensity, spatial and temporal distribution over North China has its own particularity. Due to the regionality characteristic, it is difficult to summarize in one weather mode. Objective partitioning can be used in establishment of precipitation forecast mode. Similar samples in the weather region are combined together. Regional forecast mode is more stable than single-station forecast mode, because the number of large-class precipitation samples is increased. In addition, sample data time selection is important for objective precipitation forecast modeling process.Based on the data of daily precipitation at 703 weather stations over North China from 1981 to 2007, which covers the domain of 32°—42°N, 110°—124°E, the temporal and spatial distribution characteristics are analyzed with Rotated Empirical Orthogonal Function (REOF) method. REOF analysis manifests that precipitation fields may be divided into 7 divisions. Mann-Kendall test and running t-test are used to analyze about the temporal change characteristics of different regions over North China during summer, in order to investigate the beginning and ending dates of rainy season specifically. The 7 divisions are different in precipitation beginning and ending dates. The initial date and final date of rainy season over North China are set up, and their dates are further identified, showing obvious regional features. Rainy season begins the earliest and ends the latest in the mountainous areas of the northeast of North China. It begins the latest in the central part of North China, and it ends the earliest in the southeast of North China. The concentration of precipitation time is different from the natural seasons. The long-term variation trend of precipitation anomalies in various regions and their stage are studied.