A perfect storm of drought, poverty and armed conflict in Africa's Lake Chad basin could fuel Europe's migrant crisis if world leaders fall short at two crucial summits on migration and climate change this year, a UN official warned.

The two-day EU-African summit in the Maltese capital Valletta which begins on November 11 and the UN COP21 climate conference in Paris at the end of the month must tackle long-festering problems in the region, Toby Lanzer, the UN regional humanitarian coordinator for the Sahel, told AFP this week.

Both summits address key issues which are keenly felt by countries in the drought-stricken Lake Chad basin, where 2.5 million people have been displaced, some of whom have already crossed international borders to escape the Islamist militant group Boko Haram, he said.

"Asylum seeking, the refugee crisis, the environmental crisis, the instability that extremists sow -- all of those issues converge in the Lake Chad basin," Lanzer said.

"So there's a very compelling reason why the international community needs to step up and do more."

The world must help Lake Chad basin countries Chad, Niger, Nigeria and Cameroon to not only end the militant scourge but also tackle the effects of climate change, he said.

Vast expanses of the lake have dried up and deprived people of their livelihoods of fishing, livestock farming and trade, he added.

- 'Going pear-shaped' -

Britain, France and the United States already work with the four regional countries to tackle the instability caused by Boko Haram.

But there are growing concerns the unrest could spread due to potential links between Boko Haram and like-minded extremists in places like Libya and Mali, Lanzer said.

Added to that, economic development and jobs are also badly needed for the region's burgeoning youth population who have few opportunities outside drugs and gun-running, people-smuggling and joining rebel groups.

"It's quite striking that... all the ingredients of this (are) going pear shaped.

"It's not only the fact that people are very poor: the fact there is instability, the fact there is tremendous environmental degradation, it's further compounded by a demographic situation," he said, citing the example of the Sahel where the population is seen growing by up to 150 million people over the next three decades.

With so many problems, it was time for the world to act, "to nip things in the bud" to prevent the situation from deteriorating.

The expected EU announcement in Valletta of a 1.8 billion euro trust fund for Africa, "is a very concrete and welcome step," he said, expressing hope that other countries such as the United States would join the effort.

"Valletta is a very important moment. It is a call to action for all of us," he added.