5.3 Update on El Niño or La Niña

According to the Australian Government Bureau of Meteorology, the El Niño phenomenon continues to persist in the tropical Pacific. Atmospheric and oceanic indicators of the El Niño-Southern Oscillation (ENSO) reflect a mature El Niño phenomenon. Sea surface temperatures (SSTs) across the tropical Pacific remain above El Niño thresholds, with warmer than average SSTs supporting elevated surface temperatures. In the atmosphere, cloud, wind, and pressure patterns are consistent with El Niño conditions. Climate model forecasts indicate the central to eastern Pacific may continue to warm, with SSTs likely to remain above El Niño thresholds into the early austral spring 2024. Overall, the ocean-atmosphere coupled system reflects an intensification of the El Niño phenomenon.

Figure 5.4 shows the evolution of the standard Southern Oscillation Index (SOI) values from October 2022 to October 2023. Over the past four months, SOI values have remained negative and in a consistently low range (close to or below -7), with a downward trend from July to September, dropping to -12.7 and -13.6 in August and September, respectively, before bouncing back up in October. Three-month average SOI values of -7 or lower are an important indicator for the occurrence of El Niño events.

Figure 5.4 Monthly SOI-BOM time series from October 2022 to October 2023(Source: http://www.bom.gov.au/climate/enso/soi/)

Another commonly used measure of El Niño events is called the Oceanic Niño Index (ONI). Figure 5.5 shows the locations of several NINO indices and their values for October 2023. The values for the three key NINO indices in October 2023 are: NINO3 +2.0℃, NINO3.4 +1.24℃, NINO4 +1.59℃. This means the average sea surface temperatures across these three regions are markedly above historical average levels.

  Figure 5.5 Map of NINO Region（Source: https://www.ncdc.noaa.gov/teleconnections/enso/sst）

Sea surface temperatures (SSTs) for October 2023 (Figure 5.6) were above average across the central and eastern tropical Pacific, exceeding El Niño thresholds. International climate models indicate the central and eastern tropical Pacific may continue to warm further. All models surveyed indicate sea temperatures will remain above El Niño thresholds into the early austral spring 2024.

Figure 5.6 Monthly temperature anomalies for October 2023(Source: http://www.bom.gov.au/climate/enso/wrap-up/#tabs=Sea-surface)

Table 5.2 ONI (℃) Anomaly Values from September 2023 to October 2023(Source: https://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices)

According to the latest forecasts from NOAA's Climate Prediction Center, at least a "strong" El Niño event (≥1.5℃ for ≥3.4℃) is likely to persist through January-March 2024. In the November-January season, the event has a 35% chance of becoming "historically strong" (≥2.0℃). Stronger El Niño events increase the odds of El Niño-related climate anomalies but do not necessarily equate to severely impactful events. In summary, the El Niño event is expected to continue through northern hemisphere spring, with a 62% chance during April-June 2024.

Global implications

Global warming continues to influence Australian and global climate. Global sea surface temperatures (SSTs) from April to October were the highest on record. Since national records began in 1910, Australia’s climate has warmed by 1.48 ± 0.23°C. El Niño often brings drier conditions to parts of Australia, Southeast Asia and southern Africa, increasing risks to agricultural production and wildfires. Pacific jet streams and tropical cyclone activity may also be affected.

The occurrence of El Niño not only leads to climate anomalies in Southeast Asia, Australia, and Africa but also typically results in flooding in southern China, drought in the north, drought in India, increased rainfall in East Africa, reduced rainfall in Southeast Asia, and humid conditions with abundant rainfall in the Gulf of Mexico region, including Texas and Florida. Along the Pacific coast, the northwestern United States and the Rocky Mountain region are prone to drought during El Niño events. Additionally, El Niño events usually bring increased precipitation to southern South America, the southern United States, the Horn of Africa, and certain areas in Central Asia, potentially leading to flooding issues.

Figure 5.7 The “23.7” Catastrophic Flood in the Haihe River Basin (Source: China floods: More than a million displaced as Hebei region reels after record rains | CNN)