Predictability and prediction of decadal hydrologic cycles: A case study in Southern Africa

Decision makers in drought-prone regions of the world and in international organizations responsible for drought relief require advance information, preferably on the decadal timescale, of future hydro-meteorological conditions. Focusing on Southern Africa (SA), a region subject to droughts, we used indices of four decadal climate variability phenomena, statistically associated with Self-calibrating Palmer Drought Severity Index (SC-PDSI), hindcast/forecast by the MIROC5 Earth System Model from 1961 to 2019–2020, in a statistical prediction system (SPS) to assess SC-PDSI predictability. The SA-averaged correlation coefficient between hindcast and observations-based SC-PDSI increased from 0.2 in the 1980s to 0.33 in the 2001 to 2009–2010 period; grid point correlations within SA increased from 0.4 to over 0.7 during the last 30 years. The MIROC5 – SPS system forecasts that SA may experience a moderate drought from 2014 to 2016, followed by a wet period around 2019. These hydrologic event forecasts are predicated on the absence of major low-latitude volcanic eruptions during the prediction period.