Characteristics of hourly precipitation in Tianjin

Based on the hourly rain-gauge data from 205 automatic weather stations (AWS) in Tianjin area during the period of 2009-2013, the basic precipitation distribution and diurnal variation characteristics were analyzed. The results show that there are several high value areas of precipitation hours and hourly precipitation intensities in Tianjin, located in northern mountainous area of Jixian, northwest of the main urban area and the central and south in Binhai New Area. The peak of cumulative precipitation in central and north of Tianjin mainly appears around 23:00-3:00, while it in south mainly appears around 17:00-19:00 and 4:00-8:00. The hourly precipitation intensities are similar to the cumulative precipitation and the lowest value is at 11:00. The peak of precipitation frequency generally appears around 0:00-9:00. The precipitation frequency in early evening to midnight is less than that in the early morning. The maximum value of long duration precipitation often appears in the early morning to morning, while the short duration precipitation often appears in the early evening to midnight. For most times from evening to midnight, the precipitation, precipitation frequency and precipitation intensity in urban areas are stronger than its surrounding areas and coastal areas. But in the morning opposite is true. In Tianjin, precipitation with onset time from afternoon to the evening commonly is short duration precipitation, while precipitation with onset time from the evening to early morning is often long duration precipitation.