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 value is now at -0.7 in May down from normal value of 0.0 in April suggesting the development of El Niño conditions. This is supported by increased positive SST anomalies in NINO 3.4, NINO 4 and NINO1&2 monitoring regions which have increased over the last one month with values of +1.03°C, 1.09°C and 2.43°C respectively in May. The western Indian Ocean basin has continued to warm up substantially, the WIO SST index is at +0.52°C in May from +0.43°C in April indicating significant 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 El Niño conditions are present and persistent. Enhanced convection is amplified over the central and eastern equatorial Pacific and suppressed convection over the Indonesian basin is entrenched. Collectively, these atmospheric and oceanic features reflect an ongoing and strengthening El Niño conditions. Currently a majority of model forecasts predict El Niño conditions (90% chance) will continue through the Northern Hemisphere summer 2015, and a greater than 85% chance that these conditions will strengthen and last through the rest of 2015 with a favorable chance of a strong event (3-month values of the Niño -3.4 index +1.5°C or greater). In some locations, certain impacts often associated with El Niño may appear during the Northern Hemisphere through the summer 2015 season.
Cumulative NDVI anomalies for Africa for March 2015 to May 2015 still show positive anomalies concentrated in South Sudan, northwestern Ethiopia and Somalia even though the patterns are not spatially coherent. 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 March 2015 to May 2015, the RVF persistence model does not identify any areas where ecological conditions would support the emergence of RVF vectors. Therefore there is no risk of ecologically coupled RVF activity at present. However the above normal rainfall conditions currently in other regions of the continent could lead to outbreaks of numerous vector and water-borne diseases.