Analysis of Daily Rainfall and Spatiotemporal Trends of Extreme Rainfall at Paraná Slope of the Itararé Watershed, Brazil

Abstract The knowledge of intensity and frequency of rainfall allows establishing predictive measures to minimize impacts caused by high volume of rainfall totals in a region. Therefore, the objective is to evaluate daily rainfall for Paraná slope of the Itararé watershed (PSIW) and to verify the spatiotemporal trend of intense and extreme daily rainfall. Rainfall data from 14 stations collected from 1976 to 2012 were used with less than 4% of data faults. Multivariate analysis based on cluster analysis technique (CA) was used applying the Euclidean distance for the identification of homogeneous groups, and the quantiles technique to classify daily rainfall. The Mann-Kendall (MK) test was used to identify trends for annual rainfall totals, annual number of rainy days (ANRD) and for the occurrence of intense (R95p) and extreme (R99p) rainfall. The CA technique identified three rainfall groups (HG I, II and III). Given the latitudinal position of the area, rainfall at the southern sector is characterized by its greater similarities with the subtropical climate, whereas in the North sector there is a consistent reduction of rainfall totals in autumn and, especially, during winter months, which are characteristic of the tropical climate. The MK test identified the downward trend of ANRD, with greater significance for the south-centered sectors of the basin. The observed trends for the intense (R95p) and extreme (R99p) daily rainfall show the predominance of reduction for the Southwest and central sector, followed by a significant increase in the Southeast and North sectors of the PSIW.

摘要 掌握降雨强度与频率的相关知识，可为制定预测性防控措施提供依据，以最大程度降低区域内强降雨总量所引发的各类影响。为此，本研究以伊塔雷雷流域巴拉那斜坡（Paraná slope of the Itararé watershed, PSIW）为研究区域，旨在评估该区域的日降雨特征，并探究极端强降雨事件的时空演变趋势。本研究采用了1976年至2012年间14个气象站点的观测数据，数据缺失率低于4%。研究运用基于聚类分析（Cluster Analysis, CA）技术的多元分析方法，以欧氏距离（Euclidean distance）作为相似性度量指标，识别降雨均一性分组；同时采用分位数法对单日降雨量进行分级分类。此外，本研究借助曼-肯德尔（Mann-Kendall, MK）检验，分别分析了年降雨总量、年降雨日数（Annual Number of Rainy Days, ANRD），以及强降雨（R95p）和极端降雨（R99p）事件的变化趋势。聚类分析结果显示，该区域可划分为3个降雨组（HG I、II和III）。鉴于研究区域的纬度位置，流域南部的降雨特征更接近亚热带气候；而北部区域在秋季，尤其是冬季的降雨总量呈现显著减少，这一特征与热带气候的特点相符。曼-肯德尔检验结果表明，年降雨日数整体呈下降趋势，且在流域南部集中区域这一趋势的显著性更强。针对强降雨（R95p）与极端降雨（R99p）的日降雨序列分析显示，流域西南部及中部区域的降雨事件以减少趋势为主，而东南部与北部区域则呈现显著增加的变化趋势。