Bab al-Mandeb and the Rupiah: When Red Sea Displacement Becomes Shipping-Risk Arithmetic

Rupiah Stability Watch · 2026-09-13

The premise

The first fact is human, not financial: Al Jazeera reported that about 1,400 people fled Yemen for Djibouti within 24 hours, citing Djibouti’s economy and finance minister, after an earlier group of 500 people reached Obock when boats ran out of fuel crossing the Bab al-Mandeb strait. The International Organization for Migration also warned that at least 46,000 people had been displaced inside Yemen since fighting escalated last week, with families fleeing for the second or third time and access to assistance becoming harder. That is the center of the story, not a footnote to it.

The rupiah question comes after that. A displacement surge near Obock is not a currency variable by itself. It becomes economically relevant only because it is occurring alongside a reported shift in control around the Bab al-Mandeb — the southern gate of the Red Sea and the route into the Suez corridor. Al Jazeera reported on September 11 that Houthi fighters had seized Mocha, reached Dhubab, and moved onto Mayyun, or Perim, Island after government forces withdrew. NPR, citing the Associated Press, reported on September 12 that both a Yemeni government military official and a Houthi official confirmed the capture of Mayun.

For Rupiah Stability Watch, this extends earlier work on “War-Risk Insurance,” the “Strait of Hormuz Toll Regime,” “Oman Oil Spill and the Rupiah,” “Sanctions, Carriers, and the Rupiah,” and “Brent Above $100.” Those pieces treated Hormuz as the dominant maritime-energy chokepoint. Bab al-Mandeb is different. It is not primarily a direct Indonesia oil-import gate. It is a confidence and routing gate: a place where Red Sea risk can convert into higher freight, war-risk cover, fuel burn, delayed cargoes, and a broader Middle East shipping premium.

What the evidence supports

The evidence supports five narrower claims.

First, the security geography changed. Al Jazeera’s September 11 report says Houthis took Yemen’s Red Sea coast, seized Mocha, reached Dhubab, and moved onto nearby islands in the Bab al-Mandeb. NPR’s September 12 report says Mayun’s seizure was confirmed by officials on both sides, while the Houthi military spokesman said maritime navigation remained safe except for Saudi vessels. That distinction matters: control of terrain and declared selectivity are not the same as a proven full blockade.

Second, shipping behavior has already shown stress. The National, citing preliminary Kpler data, reported that only six vessels crossed Bab al-Mandeb by 3:14pm UAE time on September 10, down from 30 on Wednesday, 26 on Tuesday, and 29 on Monday; five of the six vessels were exiting the Red Sea carrying grain, crude, coal, and fertiliser. That is a daily snapshot, not a settled trend, but it is the kind of market behavior that turns security reports into freight and insurance arithmetic.

Third, Bab al-Mandeb had already become smaller than its pre-crisis self. The U.S. Energy Information Administration’s world oil chokepoint table shows oil and petroleum-liquids flows through Bab el-Mandeb at 9.3 million barrels per day in 2023, then 4.1 million b/d in 2024 and 4.2 million b/d in the first half of 2025. The Cape of Good Hope line moved the other way, from 6.2 million b/d in 2023 to 9.3 million b/d in 2024 and 9.1 million b/d in the first half of 2025. In other words, rerouting is not hypothetical; it is already part of the system’s recent memory.

Fourth, the latest Red Sea risk is connected to Hormuz rather than separate from it. NPR reported that Mayun matters because the Red Sea route had become a key alternative for Saudi oil and other exports while Iran targeted vessels around Hormuz. The same article said Saudi Arabia had shut down a cross-country oil pipeline as a precaution after attacks, and that Saudi oil exports through the Red Sea port at the pipeline’s end had more than doubled since the February U.S.-Israel attack on Iran, according to the IEA. That makes Bab al-Mandeb an amplifier of a pre-existing Hormuz shock.

Fifth, Indonesia has a real but indirect exposure. Tempo reported in March that Pertamina imported 135.33 million barrels of crude oil in 2025, of which about 19 percent, or 25.36 million barrels, came from Saudi Arabia, with other crude from Africa, Latin America, the United States, Malaysia and others; Indonesia also maintained long-term refined-fuel supply agreements with Singapore and Malaysia. This mix means Indonesia is not simply “dependent on Bab al-Mandeb,” but landed fuel costs and replacement cargo economics can still move when Middle East shipping is repriced.

How the channel reaches Indonesia

The narrow channel from Bab al-Mandeb to the rupiah is not “refugees cause currency pressure.” That claim would be wrong and indecent. The channel is operational:

• Freight and insurance: if Red Sea transits fall and carriers treat Bab al-Mandeb as a war-risk zone, the price of moving oil products, fertiliser, grain, container inputs, and manufactured goods can rise even for cargoes that do not physically cross the strait.
• Route substitution: when Suez and the Red Sea are less usable, vessels reroute around the Cape of Good Hope. That adds sailing time, fuel burn, crew time, inventory cost, and schedule uncertainty. The EIA’s Cape of Good Hope data already show that this substitution became material after earlier Red Sea attacks.
• Energy landed cost: Indonesia’s fuel ledger is sensitive to global crude, refined-product spreads, shipping premia, and the rupiah price of dollar-denominated cargoes. A higher landed cost can pass into fiscal subsidy arithmetic before it reaches households directly.
• Food and fertiliser timing: The National’s Kpler snapshot included grain and fertiliser among vessels exiting the Red Sea. Indonesia’s exposure here is mostly indirect — world price, freight availability, and alternative cargo timing — rather than a simple single-route dependency.
• Confidence: currency markets do not need a physical shortage to price risk. They respond to whether a shock is contained, whether the policy response is credible, and whether the current account looks more vulnerable to dollar outflows.

The rupiah therefore watches Bab al-Mandeb through the same operating ledger used in the Hormuz pieces: imported energy cost, freight and insurance premia, shipping delays, fiscal cushion, and market confidence. But the route is weaker and more diffuse than Hormuz. Hormuz is closer to the core oil-flow bottleneck. Bab al-Mandeb is closer to the rerouting, Suez access, and shipping-confidence layer.

What is different from Hormuz

Hormuz and Bab al-Mandeb should not be collapsed into one headline.

Hormuz is the direct Gulf export artery. The EIA table puts the Strait of Hormuz at 20.9 million b/d of crude oil and petroleum-liquids flows in the first half of 2025, compared with 4.2 million b/d through Bab el-Mandeb. That scale difference matters. A Hormuz shock can move oil balances quickly.

Bab al-Mandeb is a second chokepoint with a different function. It governs access between the Gulf of Aden, the Red Sea, and the Suez corridor. When it is stressed, the immediate costs are often insurance, routing, delay, and effective shipping capacity. Its rupiah relevance grows when it prevents the system from using the Red Sea as the relief valve for Hormuz pressure.

That is the new arithmetic: if Hormuz risk raises the price of oil, and Bab al-Mandeb risk raises the cost of routing around or away from that pressure, Indonesia faces a compound maritime premium. Not a guaranteed rupiah fall. A thinner margin.

What the evidence does not support

The evidence does not support a claim that refugees are causing rupiah pressure. People fleeing Yemen are not a market input; they are people escaping danger.

The evidence also does not support saying Bab al-Mandeb has already moved USD/IDR. I did not find market evidence tying a specific rupiah move to the September 11–13 Red Sea reports. The correct formulation is conditional: if freight, insurance, crude, refined-fuel spreads, and import timing deteriorate, Bab al-Mandeb becomes rupiah-relevant.

It does not support calling this a generalized blockade. The Houthi statement quoted by NPR said navigation was safe for all companies except Saudi vessels. That statement may not reassure insurers or shipowners, and experts told NPR the Houthis are unpredictable, but selective targeting and market fear are not the same thing as a verified total closure.

It also does not support treating Bab al-Mandeb as Indonesia’s dominant chokepoint. For Indonesia, Malacca, Hormuz-linked energy flows, regional refined-product supply, and domestic subsidy policy remain more direct. Bab al-Mandeb matters because it can widen the global cost envelope around those more direct channels.

Watchlist for the next week

The practical watchlist is modest and observable:

1. Transit counts: whether Kpler, Vortexa, port, or AIS-based data show Bab al-Mandeb transits recovering toward normal or remaining depressed.
2. War-risk premia: whether insurers quote materially higher cover for Red Sea and Gulf of Aden exposure, and whether that bleeds into non-Saudi cargoes.
3. Carrier routing: whether container lines and tanker operators announce Cape of Good Hope diversions rather than case-by-case avoidance.
4. Fuel and refined-product landed costs: whether Brent above $100 is joined by higher clean-product freight and Asian refined-fuel premia.
5. Indonesian official signals: whether Pertamina, the Energy Ministry, ports, logistics associations, or Bank Indonesia treat Red Sea/Suez risk as an active input into supply, inflation, subsidy, or currency-stability planning.
6. Humanitarian access: whether the IOM and UN agencies can reach displaced families, or whether insecurity around the coast makes the human crisis larger.

The least-harm reading is this: keep the human crisis in the foreground, and monitor the shipping channel without exaggerating it. Bab al-Mandeb is not yet a rupiah shock. It is a second maritime stress point that can make an already expensive Hormuz world harder to absorb.