Government bonds have traditionally been regarded as among the safest investments in the financial system. Yet rising yields, falling bond prices and mounting public debt are exposing vulnerabilities in banks and financial markets. With memories of the 2023 US banking failures still fresh, could another liquidity crisis threaten the global economy, and what would the consequences be for Portugal?
By Chris Graeme
The hidden foundations of the financial system
Government bonds rarely attract the attention given to stock markets, artificial intelligence or cryptocurrencies. Yet they underpin much of the international financial system, influencing everything from mortgage rates and business investment to government borrowing and bank liquidity.
An analysis of rising bond yields and banking risks, presented in October 2026, warns that the combination of heavily indebted governments, declining bond valuations and increasingly selective investors could create dangerous pressures within the banking system.
The central concern is that banks hold substantial portfolios of government securities, traditionally considered secure investments.
However, security against default does not mean protection against market losses.
When interest rates rise, the market value of existing fixed-rate bonds generally falls. For institutions holding billions in long-dated securities, these movements can create substantial unrealised losses.
The danger emerges when banks need to convert those investments into cash quickly.
Why rising yields threaten banks
The relationship between bond yields and prices is fundamental to understanding the risks.
Consider a government bond paying a fixed annual coupon of 5%. If comparable newly issued bonds offer significantly higher returns, investors will pay less for the older security.
Its market price consequently declines until its yield becomes competitive with prevailing rates.
The precise adjustment depends on the bond’s remaining maturity, coupon payments and market conditions. Long-dated bonds are particularly sensitive to interest-rate changes.
For banks, this creates a potential mismatch between their assets and liabilities.
Depositors can demand their money back at relatively short notice, while a bank’s investments may be tied up in securities maturing over ten, twenty or thirty years.
Although a government bond may repay its face value at maturity, selling it prematurely can crystallise a substantial loss.
Furthermore, not all securities receive identical accounting treatment. Some are valued through earnings or equity, while qualifying held-to-maturity investments are generally carried at amortised cost.
This distinction means that unrealised market losses do not automatically translate into equivalent reductions in regulatory capital.
Nevertheless, they can become a serious problem when liquidity is needed urgently.
The lessons of Silicon Valley Bank
The collapse of Silicon Valley Bank (SVB) in March 2023 demonstrated how rapidly interest-rate risk can become a banking emergency.
The California-based lender had invested heavily in longer-term securities during the period of exceptionally low interest rates.
When the US Federal Reserve increased rates, those investments lost market value.
Meanwhile, SVB’s concentrated customer base of technology companies and venture-capital-backed businesses began withdrawing deposits.
The bank attempted to raise liquidity by selling securities at a loss, undermining confidence and accelerating withdrawals.
According to the Federal Reserve’s subsequent investigation, depositors withdrew more than US$40Bn on March 9, 2023, with substantially greater withdrawals anticipated the following day.Regulators closed the institution on March 10.
The Federal Reserve concluded that weaknesses in management, inadequate supervision, concentrated uninsured deposits and poor interest-rate risk management contributed to the collapse.
SVB was therefore not simply a victim of falling bond prices. Its failure resulted from several interconnected vulnerabilities.
America’s unrealised banking losses
Recent figures suggest that bond valuation risks have not disappeared.
According to the US Federal Deposit Insurance Corporation (FDIC), American banks held approximately US$326.7Bn in unrealised losses on investment securities at the end of June 2026.
This represented around 5.5% of the portfolios’ amortised cost.
Although substantial, the figure was below the corresponding percentage recorded a year earlier.
The FDIC also reported that US banks earned US$90.1Bn during the second quarter, while maintaining strong capital and liquidity levels.
These findings suggest a more nuanced situation than an imminent industry-wide collapse.
American banks remain exposed to interest-rate movements, but many possess considerable resources to absorb losses.
The principal danger lies in institutions combining substantial securities losses with concentrated deposits, inadequate liquidity or deteriorating borrower confidence.
Europe’s sovereign debt dilemma
European banks face a related challenge as governments continue financing large public debts.
The European Central Bank’s May 2026 Financial Stability Review highlighted a significant change in the composition of banks’ liquidity reserves.
As central bank liquidity declined, financial institutions increasingly replaced excess reserves with sovereign bonds.
The ECB noted that central bank liquidity had fallen by more than €2 trillion, approximately 45%, from its 2022 peak.
Although government securities qualify as high-quality liquid assets under banking regulations, they remain vulnerable to market-price fluctuations.
The ECB also warned about the relationship between government finances and banking stability, sometimes described as the sovereign-bank nexus.
If investors become concerned about a government’s ability to manage its debt, rising borrowing costs can reduce the value of bonds held by domestic banks.
Weaker banks may subsequently require government support, potentially increasing pressure on public finances.
This feedback mechanism was particularly evident during Europe’s sovereign debt crisis.
Could hedge funds accelerate a crisis?
Another vulnerability involves leveraged investors operating in government bond markets.
Hedge funds frequently use borrowed money to exploit relatively small pricing differences between securities and derivatives.
Such strategies can generate attractive returns under normal conditions.
However, sudden market movements may trigger margin calls, forcing investors to sell securities rapidly to meet collateral requirements.
If several institutions attempt to unwind similar positions simultaneously, market liquidity can deteriorate.
Banks facing deposit withdrawals could then find themselves competing with leveraged investors to sell bonds into falling markets.
This raises the possibility of a self-reinforcing cycle in which declining prices trigger additional selling.
Nevertheless, central banks retain emergency lending facilities and other instruments intended to prevent temporary market disruption from becoming systemic financial collapse.
What would the consequences be for Portugal?
Portugal is not immune to international financial turbulence, although its banking system has become considerably stronger since the eurozone debt crisis.
In its June 2026 assessment, the International Monetary Fund concluded that Portuguese banks had strong capital and liquidity buffers, supported by relatively high profitability.
The IMF also noted that banks had reduced their dependence on domestic sovereign debt, diversifying their holdings across the euro area.
However, this diversification introduces exposure to changes in bond valuations elsewhere in Europe.
The Bank of Portugal (Banco de Portugal) has similarly highlighted the resilience of domestic banks while warning that geopolitical uncertainty, financial-market volatility and pressure on households and businesses could create new vulnerabilities.
A significant international bond-market shock could increase Portugal’s borrowing costs, affect mortgage lending and discourage corporate investment.
Property development, tourism infrastructure and capital-intensive industries could be particularly sensitive to tighter financing conditions.
Higher sovereign yields could also increase the cost of servicing newly issued Portuguese government debt, potentially limiting fiscal flexibility.
A warning, not a prediction
The possibility of another banking crisis cannot be dismissed, particularly when elevated public debt, leveraged financial markets and uncertain interest-rate expectations interact.
Yet rising bond yields alone do not guarantee widespread bank failures.
The decisive factors are whether financial institutions can withstand valuation losses, retain depositor confidence and obtain sufficient liquidity during periods of stress.
Regulatory reforms introduced since 2008 have strengthened banks’ capacity to absorb shocks, while the collapse of Silicon Valley Bank demonstrated that serious weaknesses can still emerge.
For Portugal, the immediate challenge is to preserve banking resilience and maintain confidence while remaining alert to instability elsewhere.
The bond market may appear remote from everyday economic life, but its influence extends into almost every financial decision. When its foundations become unstable, the consequences can reach far beyond the trading floors.
Sources: FDIC Quarterly Banking Profile; ECB Financial Stability Review (May 2026); Federal Reserve SVB review (2023); IMF Portugal Financial System Stability Assessment (June 2026); Banco de Portugal Financial Stability Report.