Statistical characteristics of environmental parameters for warm season short-duration heavy rainfall over central and eastern China

Abstract

Water vapor content, instability, and convergence conditions are the key to short-duration heavy rainfall forecasting. It is necessary to understand the large-scale atmospheric environment characteristics of short-duration heavy rainfall by investigating the distribution of physical parameters for different hourly rainfall intensities. The observed hourly rainfall data in China and the NCEP final analysis (FNL) data during 1 May and 30 September from 2002 to 2009 are used. NCEP FNL data are 6-hourly, resulting in sample sizes of 1573370, 355346, and 11401 for three categories of hourly rainfall (P) of no precipitation (P < 0.1 mm h−1), ordinary precipitation (0.1⩽ P < 20 mm h−1), and short-duration heavy rainfall (P ⩾ 20.0 mm h−1), respectively, by adopting a temporal matching method. The results show that the total precipitable water (PWAT) is the best parameter indicating the hourly rainfall intensity. A PWAT of 28 mm is necessary for any short-duration heavy rainfall. The possibility of short-duration heavy rainfall occurrence increases with PWAT, and a PWAT of 59 mm is nearly sufficient. The specific humidity is a better indicator than relative humidity. Both 700- and 850-hPa relative humidity greater than 80% could be used to determine whether or not it is going to rain, but could not be used to estimate the rainfall intensity. Temperature and potential pseudo-equivalent temperature are also reasonable indicators of short-duration heavy rainfall. Among the atmospheric instability parameters, the best lifted index (BLI) performs best on the short-duration rainfall discrimination; the next best is the K index (KI). The three rainfall categories are not well recognized by total totals (TT) or the temperature difference between 850 and 500 hPa (DT85). Three-quarters of short-duration heavy rainfall occurred with BLI less than -0.9, while no short-duration heavy rainfall occurred when BLI was greater than 2.6. The minimum threshold of KI was 28.1 for short-duration heavy rainfall. The importance of dynamic conditions was well demonstrated by the 925- and 850-hPa divergence. The representativeness of 925-hPa divergence is stronger than that of 850 hPa. Three-quarters of short-duration heavy rainfall occurred under a negative divergence environment. However, both the best convective potential energy (BCAPE) and vertical wind shear were unable to discriminate the hourly rainfall intensities.