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 decreased to below normal values in March at -0.7 from a positive a value of 0.2 in February indicating the emergence of week El Niño conditions. Monthly SST anomalies in NINO 3.4 and NINO 4 monitoring regions have remained positive or increased with values of +0.58°C and 1.13°C respectively in March. The western Indian Ocean basin has warmed somewhat as the cooling pattern that has dominated the basin over the last two months has subsided. The WIO SST index is at 0.07°C indicating the prevalence of normal conditions over this ocean basin. The recent persistent above-average sea surface temperatures (SST) (below) in the central equatorial Pacific region are consistent with the prevalence of weak El Niño conditions. This is reflected by the recent enhanced consistent ocean-atmosphere coupling and the eastward shift of convection to the central equatorial Pacific.Convection was enhanced over the central equatorial Pacific to the Date Line over the last 3 months as shown by OLR departures below. Currently a majority of model forecasts predict weak El Niño conditions (70% chance) will continue through the Northern Hemisphere summer 2015, and a greater than 60% chance that it will last through autumn. In some locations, certain impacts often associated with El Niño may appear during the Northern Hemisphere spring and early summer 2015 season.
Cumulative NDVI anomalies for Africa for January 2014 to March 2015 show persistent positive anomalies concentrated eastern Sudan, South Sudan, northern Ethiopia and Eritrea 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 January 2014 to March 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.