This section of the report will provide a rolling three month update on a monthly basis of the state of the climatic and ecological indicators used in monitoring areas at risk to RVF activity. These indicators include, global SST anomalies patterns, Equatorial Western Indian Ocean (WIO) and Eastern Pacific Ocean (EPO: NINO 3.4) SST anomalies, Southern Oscillation Index (SOI) and Outgoing Longwave Radiation (OLR) anomalies, Rainfall and anomalies, Normalized Difference Vegetation index anomalies and RVF risk map for Africa and the Arabian Peninsula.
1. SOI and SST Indices
The SOI index has further decreased with a value of -1.6 in September from -1.4 in August, suggesting a further strengthening of El Niño conditions since early summer. This is supported by continued anomalous increase in positive SSTs in NINO 3.4, NINO 4 and NINO1&2 monitoring regions which have tremendously warmed over the last three months with values of +2.06°C, 1.04°C and 2.57°C respectively in September. The western Indian Ocean basin has continued the warming pattern with the WIO SST index at +0.84°C in September (a further record) from +0.74°C in August indicating continued warmer than normal conditions over this ocean basin. The persistent above-average sea surface temperatures (SST) (below) in the central equatorial Pacific region indicate that strong El Niño conditions are present and significantly strengthening. Enhanced convection is amplified over the central and eastern equatorial Pacific and suppressed convection over the Indonesian basin is fully entrenched. Collectively, these atmospheric and oceanic conditions reflect strong El Niño conditions are present and persisting. Currently a majority of model forecasts predict El Niño conditions (95% chance) through Northern Hemisphere winter 2015-16, gradually weakening through spring 2016. The consensus forecast is for a significant El Niño near or in excess of +2.0°C in the Niño-3.4 region(3-month values of the Niño -3.4 index +2.0°C or greater) during the peak period in December - January. In some locations, certain impacts often associated with El Niño are already manifesting during this Northern Hemisphere 2015 fall season.
Cumulative NDVI anomalies for Africa for August 2015 to September 2015 still show positive anomalies concentrated in parts of southeast Ethiopia, Somalia, Mauritania and Mali. The RVF risk map below was derived from thresholding NDVI anomaly data to detect areas persistent of above normal NDVI. Periods of widespread and prolonged heavy rainfall lead to flooding of dambos and anomalous green up in vegetation, creating ideal ecological conditions for the emergence RVF vectors. For the period August 2015 to September 2015, the RVF persistence model identifies areas does not identify any areas at risk, however given the elevated rainfall conditions, preventive measures are advised for the endemic areas of East Africa and enhanced surveillance is advised in these areas especially in the next three months (October to December 2015). The above normal rainfall conditions during this period could lead to outbreaks of other vector and water-borne diseases elsewhere.