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 continued with the trend towards normal with a value of 0.2 in February indicating the prevalence of neutral conditions. However, monthly SST anomalies in NINO 3.4 and NINO 4 monitoring regions have remained positive or increased with values of +0.57°C and 1.02°C respectively in February. The western Indian Ocean basin is currently undergoing a cooling pattern with the WIO SST index at -0.38°C indicating the prevalence of colder than 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 development of El Niño conditions. There has been weak coupling between the warm Ocean and the atmosphere and, the frequency and strength of low-level westerly wind anomalies has increased over the equatorial Pacific during the last month and a half. Convection was enhanced over the western 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 (50-60% chance) during the rest of the spring season in 2015 with no significant impacts expected as spring season contributes to progressively lower probabilities of El Niño. In some locations, certain impacts often associated with El Niño may appear during the Northern Hemisphere spring 2015 season.
Cumulative NDVI anomalies for Africa for December 2014 to February 2015 show persistent positive anomalies concentrated eastern Sudan, Eritrea, eastern Ethiopia and northern Somalia, northwestern Kenya, Botswana and NW South Africa 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 December 2014 to February 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.