@article{blain_2012,  title={Monthly values of the standardized precipitation index in the State of São Paulo, Brazil: trends and spectral features under the normality assumption},  volume={71},  ISSN={0006-8705},  url={https://doi.org/10.1590/S0006-87052012005000004},  DOI={10.1590/S0006-87052012005000004},  number={1},  journal={Bragantia},  publisher={Instituto Agronômico de Campinas},  author={Blain, Gabriel Constantino},  year={2012},  pages={122–131} }