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 maintained negative values at -0.6 in June, a minimal change from -0.7 in May suggesting the continued 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 two months with values of +1.32°C, 1.09°C and 2.54°C respectively in June. The western Indian Ocean basin has continued the warming pattern from May with the WIO SST index is at +0.4°C in June, a slight decrease from +0.52°C in May indicating continued 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 continuing to strengthen. 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) through Northern Hemisphere winter 2015-16, and around an 80% chance it will last into early spring 2016. The current conditions will continue to strengthen and last through the rest of 2015 with a favorable chance of a strong warm event. The consensus forecast is for a significant El Niño in excess of +1.5°C in the Niño-3.4 region(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 April 2015 to June 2015 still show positive anomalies concentrated in South Sudan, northwestern and eastern Ethiopia, Somalia and parts of eastern Kenya. 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 2015 to June 2015, the RVF persistence model identifies areas in South Sudan and eastern Ethiopia where ecological conditions would support the emergence of RVF vectors. Enhanced surveillance is advised in these areas. The above normal rainfall conditions could lead to outbreaks of other vector and water-borne diseases.