This work aimed to evaluate the influence of climate variability and water availability on soybean yields in western Paraná. Historical precipitation series from the Water Institute of Paraná were studied for ten municipalities in the region, with daily data from 1977 to 2015. The effects of the ENOS phenomenon during its El Niño and La Niña phases on the interannual variation of rainfall, and of the LTO on the decadal cycles of precipitation in the region were analyzed. It was found that the risks of veranicos can reach up to 20% in the month of November, while October and December presented lower risks. A strong influence of ENOS and a weak influence of the LDP on the variability of rainfall was verified. Through regression analysis, a high correlation between rainfall in the reproductive phase and soybean yield was verified. It can be concluded that the variability of rainfall in western Paraná directly affects the productivity of soybeans in the surrounding area of Itaipu.
