El Niño reduces agricultural production and productivity across Indo-Pacific low- and middle-income countries (LMICs), though effects are context specific.
1.1 The Review in Brief
El Niño reduces agricultural production and productivity in the Indo-Pacific, though its effects vary between and within countries. There is no clear evidence that El Niño and +IOD affect disease incidence or market prices consistently across the Indo-Pacific. There is no available evidence to assess effects of El Niño and +IOD on migration, conflict, and nutrition in the region.
1.2 What Is This Review About?
Climate drivers such as the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) can impact multiple sectors globally. El Niño is a climate driver that occurs in the tropical Pacific Ocean, and it is characterised by a seesaw in the sea-level pressure between the western and eastern Pacific and with a weakening of the easterly trade winds over the tropical Pacific. The IOD is the difference in sea surface temperature (SST) between the western (near East Africa) and the eastern (near Indonesia) sides of the Indian Ocean. A +IOD is characterised by higher SSTs in the western Indian Ocean region. These climate drivers may affect economic outcomes, health, migration, conflict and violence, and food security in the Indo-Pacific.
1.3 What Is the Aim of This Review?
This systematic review examines the effects of El Niño and +IOD on economic outcomes, health, migration, conflict and violence, food and nutrition security across LMICs in the Indo-Pacific region. The review summarises evidence from 89 non-randomised studies published after 1990.
1.4 What Are the Main Findings of This Review?
1.4.1 What Studies Are Included?
In January 2024, we searched 12 academic databases and 14 institutional websites and found 10,113 records. Of these, 89 unique studies (and 12 linked publications) met our inclusion criteria. The included studies spanned the period from 1992 to 2023 and were mostly from India, Indonesia, the Philippines, Malaysia, and Bangladesh. Most included studies had a high risk of bias which means their results need to be interpreted with caution. The main concerns were related to study design, specifically the failure to isolate effects of El Niño from other factors such as changes in temperature or precipitation, technological innovations, or changes in population immunity.
1.4.2 What Are the Effects of El Niño and +IOD on Health, Food Security, Socioeconomic Outcomes, Migration, Social Conflict, and Violence?
El Niño likely decreases agricultural production and productivity for LMICs in the Indo-Pacific region but has no clear effect on prices or the incidence of vector-borne diseases. Limited studies prevent conclusions on other outcomes such as aggregate production, trade, investment, household welfare, incidence of cholera, other enteric infections, direct injuries or fatalities, and respiratory infections. The findings greatly vary within and between countries. Very few studies assess the effects of +IOD in the Indo-Pacific, which makes it difficult to draw any conclusions on the effects. No studies were found on the effects of El Niño and +IOD on migration, conflicts and violence, food security, and nutrition (Figure 1).
1.5 What Do the Findings of This Review Mean?
This review highlights potential effects of El Niño and +IOD in the Indo-Pacific and underscores the need for context-specific policy responses to mitigate risks at local and regional levels.
1.6 How Up-to-Date Is This Review?
The review authors searched for studies up to January 2024. This Campbell Systematic Review was published in March 2025.