## 3 Results  
### Spatial and Temporal Patterns of the 2010-2011 Drought  
During the 2010-2011 drought, regional reductions in rainfall were evident spatially and temporally (Figures 4-6). The 2010-2011 drought, in fact, represented a significant reduction (as large as three standard deviations less) in rainfall, not only as compared to the climatology (Figures 5D and 6D), but also as compared to the region's substantial drought history (as large as 1.5 standard deviations; Figures 5F and 6F). During the previous drought years (a 'drought climatology' is presented in Figures 5B and 6B), a negative rainfall anomaly of the short rains (OND) was primarily between 40\({}^{\circ}\) E and 43\({}^{\circ}\) E, whereas the 2010 drought extended further east and with greatest intensity further westward than the average of 41.5\({}^{\circ}\) E (Figure 5E,F and Figure 6E,F). The decrease of the ensuing long rains (MAM) was one standard deviation below that of previous droughts (Figures 5B and 6B) in the southern hemisphere, exacerbating drought started in the season of short rains. In both rainy seasons, the 2010-2011 drought extended further east than in previous drought events. The 2010-2011 drought was spatially distinct from previous regional droughts. The ITCZ does not extend over East Africa during the rainy seasons but its spatial coherence over the West Indian Ocean can be considered as a proxy for moisture transport to East Africa because the Indian Ocean temperature alters the local Walker Circulation [13]. East Indian Ocean SST is warmer than West Indian Ocean SST (Figure 7), and this east-west gradient in the SST pattern has been associated with droughts in East Africa [13]. A strong negative correlation exists between SSTs in the tropical Indian and Pacific Oceans and East African rainfall [39]. In August and September of 2010, the precipitation that eventually became the southern maximum of the West Indian Ocean double ITCZ was significantly reduced in intensity and showed a less robust spatial integrity than was evident in the climatology (Figures 6 and 7). Anomalously low precipitation over the western Indian Ocean in the months preceding the OND long rains yielded a reduced westward extension of the southern ITCZ and correspondingly reduced water vapor transport to East Africa. Ultimately, this resulted in less distinct double ITCZs over the West Indian Ocean and reduced precipitation over East Africa. Figure 4: The 2010–2011 drought (red) represented a significant reduction of productivity (SIF and NDVI, Normalized Difference Vegetation Index) as compared to the mean annual cycle (thick black line) of different precipitation products averaged over the drought region. Figure 5: The 2010–2011 drought was spatially and temporally unique. The left column represents monthly rainfall climatology (GPCP) (**A**), drought climatology (alternatively referred to as a drought composite—an average of previous regional droughts (**B**), and 2010–2011 rainfall (**C**). Cool colors represent high rainfall. The right column represents average rainfall anomaly (B minus A) during drought years (**D**), 2010–2011 rainfall anomaly (C minus A) (**E**), and drought anomaly (E minus D or precipitation anomaly as compared to the drought composite average anomaly) (**F**). Brown values represent anomalously low rainfall whereas blue values represent greater than expected (anomalously high) rainfall. The anomaly was averaged along the longitude between 38.5\({}^{\circ}\) E and 46.5\({}^{\circ}\) E.  
Failed formation of the double ITCZ over the West Indian Ocean continued into the MAM season, a season with a typically weaker double ITCZ (Figure 7). Precipitation in the West Indian Ocean was  
Figure 6: Similar to Figure 5, but the anomaly was averaged along the latitude between 1.5\({}^{\circ}\) S and 4\({}^{\circ}\) N.  
Figure 7: The climatology of sea surface temperature (HadjISST, \({}^{\circ}\)C) and TRMM rainfall (mm/day) over the Indian Ocean during both rainy seasons. The East Indian Ocean is warmer than the West Indian Ocean.