The 12-day meeting of parties to the United Nations Convention to Combat Desertification (UNCCD), known as COP16, has already seen announcements that billions of dollars will be made available to respond to drought and restore damaged land.

But it has also featured stark warnings about how land is becoming drier and less productive, with many vulnerable countries lacking the necessary means to reverse the trend.

Ahead of the Riyadh talks, which opened on December 2, the UNCCD said 1.5 billion hectares (3.7 billion acres) of land must be restored by decade's end and that at least $2.6 trillion in global investments were needed.

"Where is the money? That is where the challenge is," Marcos Neto, director of the bureau for policy and programme support at the UN Development Programme, told AFP.

"The transition to a green economy has a cost, right? In the trillions of dollars. So, if you want to create a transition, we need the finance."

He added that, when it comes to land restoration, some money "is already flowing" and "we need to prioritise the process and use the resources that exist".

The first week of the Saudi-hosted talks saw pledges of more than $12 billion from bodies like the Arab Coordination Group, a collection of national and regional institutions, and the Riyadh Global Drought Resilience Partnership, which is meant to mobilise public and private money to help at-risk countries.

On Wednesday the UNCCD touted smaller commitments of 11 million euros from Italy and 3.6 million euros from Austria to support implementation of the Great Green Wall initiative stretching across Africa.

At the same time, UNDP issued a new report showing that continued land degradation will cost war-scarred Yemen $90 billion in lost economic output and lead to 2.6 million more people suffering from "undernutrition".

Ahead of Friday's conclusion, one "major sticking point" among negotiators has been whether the talks should produce a binding agreement on how to respond to drought, Neto said.

"There are some countries here that want a binding protocol on drought to be created. There are other countries that don't want it to be binding," he said.

The UNCCD brings together 196 countries and the European Union.