LIGHT RAIN CHARACTERIZATION IN PIRACICABA, SÃO PAULO STATE, BRAZIL

ABSTRACT The disorderly soil occupation without the necessary conservationist practices leads to impacts on the local hydrology and induces the pollution of water resources. This pollution may come from more urbanized areas due to the amount of pollutants drained during the rains. Even moderate precipitations constitute one of the main factors that define pollutant runoff on the surface. These rains have recently been called light rains. Light rains have a lower precipitation height and a higher frequency compared to classic rains of drainage projects, being necessary to define them according to patterns of rain frequency for each region. This study aimed to characterize light rain in the municipality of Piracicaba to establish statistical standards for the frequency of certain precipitation heights. A database provided by the ESALQ/USP automatic weather station, which provides precipitation measurements every 15 minutes, was used in the present study. Light rain heights reached 40.3, 41.4, and 42.7 mm for 100, 90, or 80% frequencies, respectively, which implies the use of return periods of 1.00, 1.11, and 1.25 years, respectively.

摘要 未采取必要保护措施的无序土地开发，会对当地水文循环造成负面影响，并引发水资源污染。此类污染多源自城市化程度更高的区域，由降雨过程中冲刷携带的大量污染物所导致。即便降水量中等的降雨，也是决定地表污染物径流的核心影响因素之一，这类降雨近期被称为小雨（light rains）。与排水工程设计所用的典型降雨相比，小雨的降水量更小、发生频率更高，因此需结合各区域的降雨频率特征对其进行界定。本研究旨在对皮拉西卡巴市（Piracicaba）的小雨特征进行分析，以建立特定降水量级的频率统计标准。本研究采用了ESALQ/USP自动气象站（automatic weather station）提供的数据库，该站点每15分钟记录一次降水量数据。在100%、90%和80%的发生频率下，小雨的降水量分别可达40.3 mm、41.4 mm和42.7 mm，对应重现期分别为1.00年、1.11年和1.25年。