Growing-season rainfall and scenarios of future change in southeast Africa: implications for cultivating maize

Global climate change is a detectable and attributable global phenomenon, yet its manifestation at the regional scale, especially within the rainfall record, can be difficult to identify. This problem is particularly acute over southern Africa, a region characterised by a low density of observations and highly dependent on rural agriculture, where the impact of rainfall changes on maize cultivation critically depends on the timing with respect to the crop phenological cycle. To evaluate changes in rainfall affecting maize cropping, daily rainfall observations from 104 stations across Malawi, Mozambique, Zambia and Zimbabwe were used to detect trends in planting dates, rainfall cessation and duration of the rainfall season, as well as number of dry days, length of dry spells and measures of rainfall intensity during critical periods for growing maize. Correlations with the Southern Oscillation Index (SOI) and Antarctic Oscillation (AAO) were used to infer how large-scale climate variability affects these attributes of rainfall and highlight where (and when) trends may contribute to more frequent crossings of critical thresholds. The El Nio Southern Oscillation (ENSO) was associated with changes in planting and cessation dates as well as the frequency of raindays during the rainfall season (particularly early in the season). AAO mainly affected raindays towards the end of the season when maize was planted late. Trends are discussed relative to changes projected in empirically downscaled scenarios of rainfall from 7 general circulation models for the 2046-2065 period, assuming an SRES A2 emissions scenario.