The Night the Plumbing of the Financial System Seized
In 2019 the market where banks borrow overnight suddenly spiked, forcing the central bank to intervene. It revealed how little margin the system had, and how poorly understood its plumbing was.
The Market Nobody Watches Until It Breaks
Banks and other institutions constantly borrow and lend cash overnight, secured against safe collateral, in a market called the repo market. It is the plumbing of the financial system, invisible and dull, moving vast sums each day at rates that normally sit close to the central bank target.
In 2019 this plumbing suddenly failed. Overnight repo rates, which should have been near a couple of percent, spiked to several times that level in a single day, signalling that the system had abruptly run short of cash. Nothing was collapsing, no crisis was underway, and yet the most basic funding market seized up, forcing the central bank to intervene.
The spike was not caused by a crisis. It was caused by the ordinary system running out of the cash it needed on a normal day, which was more alarming than a crisis would have been.
What Actually Happened
The cause was mundane, a collision of predictable events that together drained cash from the system at the same moment. Two ordinary things coincided: a corporate tax payment date pulled cash out of the banking system to the government, and a large settlement of newly issued government bonds required buyers to pay out cash.
| Event | Effect |
|---|---|
| Corporate tax payments | Drained cash to the government |
| Government bond settlement | Required large cash payments |
| Reserves already reduced | Little cushion to absorb the drain |
On their own, each was routine. Together, against a banking system whose reserves had already been reduced by earlier balance sheet shrinking, they drained more cash than the system could comfortably supply. Rates spiked as institutions competed for suddenly scarce cash.
Why It Was Alarming
The spike was alarming precisely because nothing was wrong. There was no failing bank, no crisis, no panic. The system simply did not have enough reserves to handle a normal day with two ordinary events coinciding.
This revealed that the earlier reduction of reserves, through balance sheet shrinking, had gone further than anyone realised, leaving the system with too little margin. The threshold at which reserves became scarce had been crossed without warning, because that threshold was not known in advance and was discovered only when it was breached. The plumbing had been running closer to its limit than its operators understood.
The Intervention
The central bank responded quickly, injecting cash into the repo market to bring rates back down and then continuing to supply reserves to rebuild the cushion. It effectively reversed part of its earlier balance sheet shrinking, adding reserves back into the system to restore the margin that had been drained too far.
The episode ended the previous program of reducing the balance sheet, since it demonstrated that reserves had fallen to the point of scarcity. The central bank had learned, uncomfortably, that it had misjudged how many reserves the system needed, and it moved to hold more than it had planned.
The Lessons
The episode taught several things about the modern financial system. First, that the level of reserves the system needs is larger and less predictable than assumed, and that draining reserves is dangerous near the threshold because the threshold is invisible until crossed.
Second, that the plumbing matters. The repo market is dull and ignored until it fails, and its failure can transmit stress through the whole system, since so much borrowing depends on it functioning smoothly. Understanding and monitoring this plumbing became a higher priority afterward.
Third, it foreshadowed the difficulty of shrinking a central bank balance sheet, showing that the process can hit a wall suddenly. This lesson shaped later efforts to reduce the balance sheet more cautiously, with tools designed to prevent a repeat, including a standing facility to supply cash against collateral automatically when rates rise, a backstop meant to stop such a spike happening again.
The Bottom Line
The 2019 repo spike saw overnight funding rates jump several times over in a single day, not because of any crisis but because two ordinary events drained cash from a banking system whose reserves had been reduced too far. It revealed that the level of reserves the system needs is larger and less predictable than believed, and that the invisible threshold of scarcity is discovered only when crossed. The central bank injected cash and stopped shrinking its balance sheet, and the episode reshaped how it manages reserves, including a standing backstop meant to keep the plumbing from seizing again.