What is a famine and who declares one?

For months, U.N. officials, aid groups and experts have warned that Palestinians in Gaza are on the brink of famine.

Earlier this month, Israel eased a weekslong blockade on the territory as a result of international criticism, but the U.N. humanitarian aid office said Friday that deliveries into Gaza remain severely restricted, describing the current flow of food as a trickle into an area facing catastrophic levels of hunger.

Gaza's population of more than 2 million people relies almost entirely on outside aid to survive because Israel's 19-month-old military offensive has wiped out most capacity to produce food inside the territory.

Israel said it imposed the blockade to pressure Hamas into releasing the hostages it holds and because it accuses Hamas of siphoning off aid, without providing evidence. The U.N. says there are mechanisms in place that prevent any significant diversion of aid, though aid trucks have been robbed and hungry crowds have broken into aid warehouses a few times.

No famine has been formally declared in Gaza.

Here's a look at what famine means and how the world finds out when one exists.

What is famine?

Famine can appear in pockets — sometimes small ones — and a formal classification requires caution.

Last year, experts said a famine was ongoing in parts of North Darfur in Sudan. Somalia, in 2011, and South Sudan, in 2017, also saw famines in which tens of thousands of people were affected.

Gaza poses a particular complication for experts since access is severely limited, making gathering data difficult if not impossible in some cases.

Last year, the IPC said an area can be classified as in ''famine with reasonable evidence'' if two of the three thresholds have been reached and crossing the third appears likely to have happened.

The IPC unites experts from more than 20 organizations like the U.N.'s health, development, and food aid agencies; charity CARE International; the Famine Early Warning Systems Network; and the European Union and the World Bank.

The short answer is, there's no set rule.

While the IPC says it is the ''primary mechanism'' used by the international community to analyze data and conclude whether a famine is happening or projected, it typically doesn't make such a declaration itself.

Often, U.N. officials or governments will make a formal statement, based on an analysis from the IPC.

''There's a widespread misunderstanding that someone has to declare a famine before it is a famine. That is not the case,'' said Jens Laerke, a spokesman for the U.N. Office for the Coordination of Humanitarian Affairs. ''When IPC shows the data that hits the threshold for a famine, then it's a famine.''

What happens when a famine is declared?

A small amount of food is entering Gaza again following the 2 1/2-month Israeli blockade. But aid groups say it is a fraction of what is needed — and gunfire and chaos have plagued food distribution in recent days.

The Israeli military says it has facilitated the entry of nearly 1,000 trucks the past 12 days, far below the rate even at the highest times during the war when several hundred trucks a day would enter.

In general, international preparation and effective deployment in response to famines can be lacking.

''There is not a big, huge bank account'' to draw on, said OCHA's Laerke. ''The fundamental problem is that we build the fire engine as we respond."

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