Abstract
Significant hindcast skill for the 3-month standardized precipitation
index (SPI$_{3M}$) has been so far limited to one lead month. To
increase that lead time, we propose to exploit well-known El
Ni\~no-Southern Oscillation
(ENSO)–precipitation teleconnections through ENSO-state conditioning.
We condition initialized seasonal SPI$_{3M}$ hindcasts, derived
from the Max-Planck-Institute Earth System Model over the period
1982-2013, on ENSO states by exploring significant agreements between
two complementary analyses: hindcast skill ENSO–composites, and
observed ENSO–precipitation correlations. Predictions conditioned on
autumn (ASO)-ENSO states demonstrate significant and reliable winter
(DJF) drought hindcast skill up to lead month 4 in equatorial South- and
southern North America. The area of reliable drought hindcast skill is
further enlarged when the respective region’s dry ENSO phase is already
present in the antecedent summer (JJA-ENSO-state-conditioned). In
contrast to previous studies, our evaluation separates predictions and
observations. Thereby, ENSO-state conditioning demonstrates genuine
hindcast skill up to lead month 4.