Winter is coming in Gaza, and the long nights and heavy rains will deepen the misery of thousands of families whose homes were destroyed in the fighting of summer.
Newly homeless in a place already peopled with the descendants of refugees from the war that followed Israel's creation in 1948, their plight is desperate.
The level of damage in parts of Gaza is extraordinary - the UN Secretary General, Ban Ki-moon, called it "destruction beyond description".
No-one who has seen at first hand the power of modern missiles and artillery shells could fail to be awed by the destructive forces they unleash.
Huge buildings fashioned from thousands of tonnes of concrete have been reduced to dense, shallow, uneven mounds of rubble, as though they had been sucked in on themselves.
In some places - such as Shejaiya and Johr El-Deek - the pattern is repeated from house to house and street to street.
So when the International Donor Conference in Cairo ended with pledges to Gaza that added up to about $5.4bn (£3.4bn), it appeared to send a powerful signal that help was at hand.
The reality is slightly more complex.
First, there's the arithmetic.
Of that $5.4bn, about half has been earmarked for the direct repair of war-damage - the reconstruction of buildings, roads, electricity supply lines and sewerage systems.
It is not immediately clear how the rest of the money will be spent - but Gaza has no shortage of needs.
Money is desperately needed to improve the water supply, sewage disposal and road system among many other infrastructure issues.
And of course there is a continuing problem with funding the Hamas-run ministries of Gaza. Public-sector salaries are hugely important in a place where the private-sector economy has had the life squeezed out of it by an Egyptian and (mainly) Israeli economic blockade.
When they went unpaid for months earlier this year, the public pressure on the Hamas leadership was one of the factors that pushed it towards conflict with Israel - the argument being that Hamas knows it is in a better position to demand political concessions in times of conflict than in times of quiet.
So spending the money won't be a problem. Sadly, collecting might be.
It is a simple truth that governments do not always honour pledges they make to good causes at moments of international crisis.
Palestinian officials have said that most of the money pledged after Gaza's conflict with Israel in 2009 for example never came.
So for the moment that $5.4bn has a rather theoretical feel to it - but it is reasonable to assume that a substantial amount of money is on its way.
All of the donor countries are no doubt motivated by a desire to help the people of Gaza. Some have their own political and strategic motives for getting involved too.
The largest single donors, Qatar ($1bn) and Saudi Arabia ($500m), are rivals for influence throughout the Middle East and the Islamic world. The same can be said of both Turkey and the United Arab Emirates ($200m each).
The United States ($212m) and the European Union ($568m) may see their contribution as part of the price of continuing to play a role in the wider Middle East - aside from any humanitarian concerns they might also feel.
Individual European countries such as the United Kingdom ($32m) are no doubt motivated by a similar mix of considerations.
Politically, the winner in all this should be the Palestinian Authority (PA) led by Mahmoud Abbas.
At the moment, the PA, which controls the West Bank, has formed a unity government with Hamas, the militant Islamist organisation that controls Gaza.
But Western powers in particular are determined that the reconstruction funds will pass through the hands of the PA - partly to bolster its standing as a more moderate force and partly to stop Hamas from using the money directly to re-arm.
And there is another, even more interesting, political subtext to the reconstruction project.
Israel was of course not present at the donor conference. It simply would not be welcome at a gathering in the Arab world to discuss repairing the damage caused by its bombs and missiles.
But it did suffer a kind of political defeat in Cairo.
During the fighting, it was insistent that it would link any reconstruction funding to moves aimed at disarming or demilitarising Hamas. But no-one is now talking in those terms, and Israel is having to settle for something much more limited.
Any material intended for the reconstruction of Gaza is going to end up passing through Israeli territory.
Egypt does have a crossing point with the Palestinian territory, at Rafah, but it argues that it is a facility suitable for people only and was not built to deal with a substantial flow of goods.
That also means of course that the entire responsibility for making sure that Hamas does not use the reconstruction effort to re-arm will fall to Israel.
Its main crossing point into Gaza, at Kerem Shalom, can handle up to 450 trucks a day.
Building materials can be bought anywhere in the world, but they will all end up at this huge freight-handling terminal.
Israel has two security concerns.
The first is simple enough. Every bag of concrete will have to be searched to make sure it does not have guns, ammunition or rocket parts hidden somewhere inside.
The second is slightly more subtle and involves what are called "dual-use" materials - in other words anything that could be used to build either houses or rocket silos, such as concrete or steel.
Israel is going to have to find a way to measure the amount that enters Gaza and then the amount that is visibly used in civilian construction - if there is a gap between the two figures, they will assume that Hamas is creaming off the difference to build bunkers and tunnels.
So the Gaza reconstruction conference provided encouraging headlines, but there is much to do before winter comes.
And overshadowing all those practical concerns is a simple political problem.
However quickly and completely those donor nations cough up the cash, the truth is that without some sort of political progress between Israel and the Palestinians - of which there is absolutely no sign - there is no guarantee that anything rebuilt in Gaza this year or next year won't simply be destroyed again in the next conflict.