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 slightly weakened in June with a value of 0.2 from 0.5 in June. These conditions generally reflect the prevalence of continued ENSO-neutral conditions across the eastern Pacific Ocean basin. June monthly SST anomalies in the NINO3.4 SST have remained steady at ~ 0.45°C and so are the WIO SST (0.3°C) anomalies indicating the prevalence of normal conditions over these ocean basins. Even though above-average sea surface temperatures (SST) (below) and in the NINO 1& 2 regions have increased and expanded over the eastern equatorial Pacific Ocean during June 2014, the absence of a clear atmospheric response to the positive SSTs indicates ENSO-neutral conditions, though the tropical Pacific continues to evolve toward El Niño. Nearly all model forecasts indicate the development warm ENSO 70% this summer (Niño 3.4 index: between 1.0°C and 1.4°C) and 80% in the fall. There are uncertainties to its evolution but projections are for at weak-to-moderate strength during the late fall and early winter with seasonal with Niño 3.4 SST values ranging between 0.5°C and 1.4°C.
Cumulative NDVI anomalies for Africa for April 2014 to June 2014 show positive anomalies concentrated over the South Sudan, western Ethiopia, Botswana, Namibia and northern South Africa following the above normal rainfall in these areas in the last several months. 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 April 2014 to June 2014, the RVF persistence model identifies areas in Kenya, Botswana, central Namibia and Sudan and South Sudan where ecological conditions would support the emergence of RVF vectors. Enhanced surveillance is advised in these areas.