Assad, Eduardo Delgado, et al. “Dry Spells in the Brazilian ‘cerrados’ Region: Frequency and Probability of Occurrence”. Pesquisa Agropecuaria Brasileira, vol. 28, no. 9, Sept. 1993, pp. 993-1003, doi:10.1590/S1678-3921.pab1993.v28.3962.