IDENTIFICATION OF HOMOGENEOUS RAINFALL ZONES DURING GRAIN CROPS IN PARANÁ, BRAZIL

ABSTRACT The aim of this study is to identify homogeneous rainfall zones in the winter and summer 1st and 2nd crops, in the state of Parana, Brazil. The zones were defined by clustering using the expectation-maximization (EM) algorithm to transform seasonal rainfall series. Monthly average rainfall data collected from 157 weather stations for 20 years (1996 to 2015) were employed. The results show that the number of homogeneous zones varied among growing seasons. The summer crop presented two clusters, with rainfall averages of 1489 and 1925 mm; the second crop presented four clusters, with averages of 1849, 1004, 1454, and 1182 mm; and the winter crop had three clusters, with averages of 969, 1498, and 1171 mm. Clustering was a useful instrument to identify geographical regions with similar rainfall regimes during different growing seasons in the state of Parana. Rainfall distribution was more homogeneous in the summer crop. In all crops analyzed, the clusters with the lowest rainfall rate were present in the northwestern, northern center, and northern pioneer of the state of Parana, whereas the clusters with the highest rainfall rate were found in the coastal regions.