The Arabian Sea is the main moisture source for the summer monsoon, on which nearly a billion people depend. Marine heatwaves here have been poorly studied: previous work focused on the Bay of Bengal, the western equatorial basin, and coastal zones of the southeastern Indian Ocean. It is known that these regions are influenced by El Niño, the Indian Ocean Dipole, and intraseasonal oscillations, but for the Arabian Sea the mechanisms of MHW generation and atmospheric responses remained unclear. This study fills that gap by linking MHWs to monsoon rainfall and extreme events.
The authors used OISST satellite sea surface temperature data for 1982–2023, ERA5 and ECCO reanalyses for heat fluxes and winds, and IMERG precipitation. Marine heatwaves were defined as periods when temperatures exceeded the 90th percentile of the seasonal cycle for at least five days. To separate the influence of anthropogenic warming, a linear trend was removed from the data. To test causal links, they ran numerical experiments with the regional WRF model, comparing runs with actual sea surface temperatures against runs with climatological temperatures lacking MHW-related anomalies. Additionally, they analyzed the mixed-layer heat budget using ECCO data.
The eastern and northern Arabian Sea have become MHW hotspots: the frequency, duration, and cumulative intensity of events have grown rapidly since 1982, mostly due to anthropogenic warming. After detrending, most MHWs are short (median duration about 9 days; 25 of 32 events in the east and 25 of 29 in the north). Short MHWs occur during suppressed convection phases of intraseasonal oscillations (BSISO): clear skies boost incoming solar radiation, while weaker winds reduce evaporation. Long MHWs (>20 days) depend on interannual temperature anomalies tied to El Niño and a positive Indian Ocean Dipole, as well as other, not-yet-identified factors. In response to the warming, a cyclonic circulation forms in the atmosphere: in the east it enhances rainfall over India's southwest coast (the risk of extreme rainfall rises by a factor of 2–3), and in the north it does so over northwestern India and Pakistan. The August 2022 Pakistan flood coincided with an MHW whose peak occurred on 8 August, and the subsequent cyclone brought extreme rainfall on 17–18 August.
This work is the first to demonstrate a two-way coupling between atmosphere and ocean in the Arabian Sea: intraseasonal oscillations spawn MHWs, and MHWs then amplify cyclonic activity and rainfall. This sets it apart from neighboring studies that treated MHWs as a passive response to the atmosphere or focused on other basins. It shows that short and long MHWs have different mechanisms, which calls for separate treatment in forecasting. The results explain why extreme rainfall in the region may be tied not only to large-scale modes but also to local ocean warming.
The topic could move toward MHW forecasting based on intraseasonal oscillation predictions, which already have good skill. This would allow warnings of extreme rainfall risk several weeks ahead. It is also necessary to investigate sources of interannual variability not related to El Niño or the dipole, which contribute comparably to long MHWs. It is important to assess how MHW frequency and intensity will change under further warming and what that means for the monsoon.
The results will affect forecasting of extreme rainfall and floods in India and Pakistan, as well as management of marine ecosystems and fisheries in the Arabian Sea.
Develop a statistical or hybrid MHW forecast model based on intraseasonal oscillation indices. Run additional numerical experiments to quantify the threshold sensitivity of the atmospheric response to the amplitude of temperature anomalies.
In atmospheric and ocean sciences, the predictability of extreme events on subseasonal timescales remains an open question. This work connects that problem to marine heatwaves, showing that accounting for oceanic anomalies can improve forecasts. Also open is the role of non-ENSO and non-IOD interannual variability in the Indian Ocean.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
Using satellite data, reanalyses, and numerical experiments, this study identifies the mechanisms behind marine heatwaves (MHWs) in the Arabian Sea: short events are linked to suppressed convection during intraseasonal oscillations, while long events are tied to interannual variability, including El Niño and the Indian Ocean Dipole. The authors show that MHWs generate cyclonic anomalies that enhance rainfall over southwestern India and Pakistan, including the 2022 floods.
Where its strength is
The strength lies in establishing a two-way ocean-atmosphere coupling in this region: MHWs are not only generated by intraseasonal oscillations but also amplify cyclonic activity and extreme precipitation. Separating the mechanisms of short and long events provides a basis for their independent forecasting.
Where it could go next
Worth trying
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.48, against a usual 0.64. It looks like few have drilled nearby.
The 2022 Pakistan flood affected about 33 million people and claimed nearly 1500 lives. The marine heatwave that preceded it peaked just ten days before the heaviest rains.
In Kim Stanley Robinson's novel The Ministry for the Future, extreme heat in India triggers a chain of climate catastrophes. In the book, the Arabian Sea also becomes a source of destructive monsoons, echoing the mechanism described in this paper.