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 was near normal in July though slightly negative with a value of -0.2 in July from a value of 0.2 in June. These conditions generally reflect the prevalence of somewhat ENSO-neutral conditions. July monthly SST anomalies in the NINO3.4 SST have decreased substantially to 0.18°C in July from ~0.45°C in June 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) in the NINO 1& 2 regions of the far eastern equatorial Pacific continued during July 2014, the remained near average in the central and east-central equatorial Pacific and in particular most of the Niño indices decreased in July. The absence of a clear atmospheric response to the positive SSTs indicates ENSO-neutral conditions. As a result, nearly all model forecasts have delayed the onset to the August - September period and decreased the chance of El Niño to about 65% to peak at weak strength during the late fall and early winter (3-month values of the Niño 3.4 index between 0.5°C and 0.9°C).
Cumulative NDVI anomalies for Africa for May 2014 to July 2014 show positive anomalies concentrated over the central Sudan, north-western Ethiopia, Botswana and Namibia 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 May 2014 to July 2014, the RVF persistence model identifies areas in Sudan and South Sudan where ecological conditions would support the emergence of RVF vectors. Enhanced surveillance is advised in these areas. These locations have reported cases Cholera over the last month due to flooding and poor sanitary conditions.