Characters Of Short-time Heavy Precipitation And Analysis And Forecast Research On Rainstorm Disasters In Jinan

The short-time heavy precipitation is difficult to forecast for its happened suddenly and large rainfall. Because of the special terrain and the unsubstantial drainage facility, it could be influent to the road traffic terribly and even threaten human life. In this study, we analyzed the short-time heavy precipitation processes since it had been recorded by the regional automatic meteorological stations and studied two rainstorm disasters.We explored the characteristics of short-time heavy precipitation processes in Jinan during 2007 to 2014 including the interannual, intermonthly and daily variation, magnitude variation and regional distribution. Besides that, the weather conditions, the physical quantity fields and the Doppler radar productions were also be discussed in the current study. We selected two serious rainstorm disasters to investigate the circulation situations, water vapour conditions, thermodynamic conditions and mesoscale dynamics conditions using the NCEP Reanalysis data. The multiple linear stepwise regression equation for predicting hourly maximum precipitation had been set up by using weather conditions and common physical quantities, as well as tested in daily forecast work. The conclusions were as follows.（1） It was an increasing trend for the days of short-time heavy precipitation in 2007 to 2014. The most frequently area in which it occurred was the southern mountain area where nearby Mount Taishan, followed was the center of the city. Short-time heavy precipitation usually happened in July and August. The earliest records was the middle of March, and it decreased rapidly in September, with no processes after the mid of September arrived. The peak intensity performed in July, and the weakest in March. For one day, it mainly rained on 18 and 19 o’clock, followed was 4 and 5 o’clock. The daily variabilities, both short-time precipitation and urban heat island effect intensity, indicated a certain degree of relationship.（2） The main weather condition patterns resulted to short-time precipitation were cold vortex, transversal trough, west wind trough, subtropical high, between the two subtropical high and typhoon reverse trough. The highest appearance probabilities were west wind trough and subtropical high, while the lowest were between the two subtropical high and typhoon reverse trough. The temperature dropped rapidly and the pressure increased when it rained. The precipitation usually shew a positive correlation with the variabilities of temperature and pressure, and whether the gale appeared was decided by the intensity of cold air.（3） There were significant increasing processes for the physical quality indexes such as K index ≥32℃, SI index <-1℃, CAPE ≥ 500J·kg-2, θse850 ≥ 75℃, and（T850-T500） ≥ 25℃, before the short-time heavy precipitation happened. There were some signs for the radar productions when the short-time heavy precipitation occurred, e.g., the radar echo strength was more than 40 dBZ and the maximum got to 70 dBZ, there were adverse wind area or wind convergence area on the basic hodographs and it is usually 15-30 minutes for adverse wind area appeared before the short-time heavy rain happened, the echo top（ET） was more than 9 km with the highest value of 12 km, the Vertical Integrated Liquid water（VIL） was larger than 20 kg·m-2 and the maximum was more than 50 kg·m-2.（4） There were four common points of weather condition for two serious rainstorm disasters: trough in westerlies, the edge of subtropical high, low vortex at the middle-inferior layer of troposphere, and the strong southwest jet at low altitudes. The strong southwest jet brought the warm and wet flow to the rainstorm area continuously resulting in the convective unstable energy raised sharply. The cold air converged with strong southwest jet at low altitude in Jinan triggering convective unstable energy released and rainstorm come. It is shown strong convergence ascending motion at low altitude during two rainstorm with K index >40℃, SI index <-2.4℃, and q>13g·kg^-1.（5） Based on the analysis of circulation situations, physical quality fields and radar productions, we chose some indexes which shared close relationships with short-time heavy precipitation to establish the multifactorial forecast procedure according to the principle of from coarse to fine by analyzing the variations of weather conditions, water vapour, atmospheric stratification stability, and the characteristics of the Doppler radar, wind profile radar and regional automatic meteorological stations. It was tested during the rainy season of 2015, with a precision rate of 60%. It played an important role in the short-time heavy precipitation during the application of daily forecast work.