Estimativa de chuvas intensas em locais sem dados no Rio Grande do Sul

Abstract

The knowledge of the intense rainfall is important in the project of several engineering works, which normally, is defined from the intensity-duration-frequency relations (IDF), allowing to estimate in a simple way the maximum intensity rainfall that can occur with a certain time of recurrence (TR). However, for the determination of an IDF, is required rainfall data with a small temporal discretization (<10-20min), with long periods of observation and few failures, which is difficult to obtain in the Rio Grande do Sul, making it difficult to determine of IDF relations. However, there is a numberless of precipitation information in RS, usually not used directly, such as daily data and estimated satellite precipitation or reanalysis data, such as the Multi-Source Weighted-Ensemble Precipitation (MSWEP). Observing the need for studies that can propose and evaluate alternative and reliable methods of estimating IDF, based on this information. In this scenario, two methodologies are proposed and evaluated, one for the estimation of the maximum daily precipitation and another for the estimation of the maximum precipitation to several durations since sub-daily until several days. To concretize these methodologies, 5 homogeneous regions of maximum precipitation for RS were initially determined, based on geographic convenience in conjunction with the measures of disagreement and heterogeneity of the L-moments presented by Hosking and Wallis (1997). First, using the daily data provided by the National Water Agency (ANA), the maximum precipitation growth curves were determined, relating the reduced Gumbel variable and the precipitation, based on the FORGEX methodology presented by Reed, Faulkner and Stewart (1999), after which the daily maximum precipitation equations determined with the aid of GAMLSS models. For the determination of maximum rainfall for several durations, the MSWEP data were used together with the hourly data provided by INMET, the equations were determined based on the L-moments along with the methodology presented by Koutsoyiannis, Kozonis, Manetas (1998). Therefore, for each of the 5 homogeneous regions of maximum rainfall of the RS, two equations are presented, one for the estimation of the daily maximum precipitation and the other for the maximum precipitations for several durations. However, the equations proposed in this work have limited of application, and it is possible to obtain the maximum daily precipitation for return time between 2 and 30 years, in relation to the maximum precipitation estimates for several durations it is possible to obtain the maximum precipitation for durations between 3 hours and 168 hours, with a return time between 2 and 50 years. Thus, with the homogeneous regions and the use of the maximum precipitation equations, it is possible to estimate the intense precipitations in the entire of Rio Grande do Sul, same in locations with no observed precipitation data.