While individual food emergencies may be triggered by events such as a poor rainy season, the chronic vulnerability to hunger is caused by a wide range of underlying factors.

Poverty

One of the very few areas of consensus is that the dominant cause of hunger in Africa is poverty.

In his seminal 1981 work, "Poverty and Famines'" the Indian economist and Nobel Prize winner Amartya Sen wrote: "Starvation is the characteristic of some people not having enough food to eat. It is not characteristic of there not being enough food to eat. While the latter can be the cause of the former, it is but one of many possible causes."

Sen's thesis of "entitlement" showed how there is almost always enough food to supply the population, but those who are in abject poverty are unable to command the resources, that is the money, to purchase the food.

Twenty-five years later, his theories remain tragically relevant. Some 315 million people - half the population of sub-Saharan Africa - survive on less than a dollar a day, according to the U.N. Development Programme (UNDP). The average life expectancy is only 41 years and less than 50 percent of the population has access to hospitals or doctors.

Very low incomes force families to sell off assets such as animals and tools in order to make ends meet. Over time this reduces their ability to cope with shocks like the failure of a rainy season because they have nothing to fall back on in times of hardship.

In the case of Niger, markets in main towns were well stocked with food even at the height of the crisis but most people could not afford it because of explosive price rises. In short, being poor makes people poorer. A government initiative to sell millet at subsidised prices in mainly pastoral zones failed to improve the situation because most people could not afford even that.

In an attempt to tackle poverty at source, the G8 club of industrialised nations unveiled a dramatic debt-reduction package at Gleneagles, Scotland in July 2005. Under the deal, the world's richest countries - with the backing of the International Monetary Fund (IMF) and World Bank - agreed to write off some $40 billion in debt owed by 18 mainly African countries. They also agreed to increase Official Development Assistance (ODA) by $50 billion by 2010.

But campaign organisations and aid agencies say the G8 has fallen far short of its promises. A pledge by G8 leaders at the 2007 summit in Germany to provide $60 billion for HIV/AIDS, tuberculosis and malaria was met with intense criticism.

Oxfam said the $60bn included considerable amounts of money from existing spending levels and was far from enough to set the G8 back on track on overall aid. The aid agency's calculations, based on the assumption that the money will be delivered over five years, show that by 2010 overall aid will only have increased by $23bn. That's $27 billion short of the Gleneagles promise.

Low agricultural productivity

According to figures from the U.S.-based Partnership to Cut Hunger and Poverty in Africa, rural families account for 75 percent of the population in Africa and a large proportion of the hungry, malnourished and poor. In addition, rural small holder farms and firms account for over 80 percent of African agricultural exports and foreign exchange earnings from agriculture.

Despite this, government investment in the sector continues to decline, along with production.

British-based NGO FARM-Africa says that Africa has turned from being a food exporter to a net food importer in the past 30 years. Crop yields are no higher today than they were in 1980 and the continent's share of world agricultural trade fell from 8 percent in 1965 to 2.5 percent in 2004.

The challenges facing Africa's agricultural sector include poor political and economic governance, inadequate funding for the agricultural sector, poor water resources management, and neglect of research and development.

Foreign investment and donor relief are also lacking.

According to Julie Howard, executive director of the Partnership to Cut Hunger and Poverty in Africa, U.S. assistance to agriculture in Africa has grown only by an estimated 2 percent in real terms since 2000. By contrast, she said, U.S. Agency for International Development (USAID) health funding for Africa health funding alone had grown by 61 percent since 2000.

In 2006, Oxfam UK said that while spending on food aid and humanitarian aid had increased, aid for agricultural production in sub-Saharan Africa had dropped by 43 percent between 1990-2 and 2000-2.

HIV/AIDS

Across the continent, but especially in the south, the spread of HIV/AIDS has irreparably damaged affected communities, compromising their capacity to cope and rendering them increasingly vulnerable to hazards and shocks.

This is particularly the case when food is scarce, creating a new profile of vulnerability to destitution and hunger.

According to the World Health Organisation (WHO), sub-Saharan Africa has just over 10 percent of the world's population, but is home to more than 60 percent of all people living with HIV, some 25.8 million.

Southern Africa is the most affected region, where HIV prevalence rates have stabilised at high levels, exceeding 25 percent in some countries, while in others the epidemic is still growing. Even in eastern Africa, where HIV prevalence is declining, the rates remain at 5 percent. Most countries in west and central Africa have stabilised at below 5 percent.

Whereas conventional famines tend to kill young children and the elderly, HIV/AIDS kills the very young adults whose labour traditionally enabled communities to cope with drought and hunger.

According to this hypothesis, known as New Variant Famine and pioneered by Alex de Waal, the burden of care for those sick with AIDS cripples families. Their livelihoods then collapse and the networks and coping strategies dissolve.

"In short," de Waal writes, "HIV is imperilling the ability of African societies to reproduce themselves."

Climate change

Across the continent, climate change and rapid desertification - particularly the southward advance of the Sahara into Sahel regions - have stripped many communities of traditional farming and pasture land.

Pastoralists need rain-fed grass to feed their cattle and the vast majority of farmers are dependent on rain-fed crops, so any disruption in the water supply can have a rapid and catastrophic effect.

Yet rains have become unreliable and at times non-existent. In the Sahel, erratic rainfall in 2004 destroyed vast swathes of pasture land. In East Africa and the Horn, poor rains in recent years were followed by the complete failure of the rains in October 2005 in Kenya and Somalia. And Southern Africa's drought follows a previous failure of the wet season, which provoked the food crisis in 2002-2003.

The Intergovernmental Panel on Climate Change (IPCC) said in a 2007 report that Africa will bear the brunt of global warming. The U.N. body predicted that an increase in greenhouse gas emissions will leave up to 1.8 million more people in Africa without sufficient clean water. Meanwhile, arid and semi-arid lands are likely to increase by up to eight per cent with profound consequences for agriculture and food productions.

Among other predictions, the report said wheat may disappear from Africa by the 2080s, that the soya bean harvest in Egypt could drop by close to 30 per cent by 2050 under a worst case scenario and that maize yields could fall significantly in Southern Africa.

Other man-made drivers of climate change include deforestation, which leads to desertification. The U.N. Environment Programme (UNEP) has said that logging is a central cause of drought in East Africa, given the role that dense vegetation such as forests plays in generating rainfall by pumping water held in soil into the air.

Since independence in 1963, Kenya's forest cover has shrunk from 10 percent of its 582,650 square-kilometre (224,962-square-mile) territory to a mere 1.7 percent, altering rain and catchment patterns that are essential for the country's agrarian economy.

Global food prices

Soaring global food prices are affecting people's ability to feed their families. In 2007 and 2008, the global price of many basics including rice, wheat and maize shot up, triggering riots in many parts of Africa.

Not surprisingly, the hardest hit are the poorest - especially the urban poor, who spend as much as 80 percent of their income on food.

The International Committee of the Red Cross has warned the situation will worsen conflict in war zones.

Countries most affected are those experiencing failed harvests forcing them to import large amounts of food. Many governments have introduced food subsidies or export restrictions to counter rising costs, but some critics say these have only exacerbated price rises on global markets.

And the rising price of food, combined with fuel price hikes, has also pushed the cost of food aid sky-high - just when it is needed most.

The prices rises have been caused by a combination of increased demand from India and China, a rise in the use of biofuels produced from food crops, a spike in transport costs, and poor harvests.

Armed conflict

Widespread conflict and the proliferation of small arms have displaced millions of people across Africa. While the Sahel and southern Africa have been relatively free of conflict in recent years, the Horn of Africa is still wracked by armed violence.

"Guns are at the heart of the problem," said Dennis McNamara, special U.N. adviser on internal displacement, calling for a voluntary cessation of all arms sales to Africa.

He added that violence has uprooted some 12.5 million Africans within their countries, representing half of the world's internally displaced. The underlying causes of hunger, such as violence and political instability could not be solved simply by handing out food, he said.

In Somalia, where 1.7 million people need assistance, there has been no central government since 1991, when the country descended into a protracted civil war.

The head of Oxfam Kenya, Gezahegn Kebede, has said that drought exacerbates conflict between nomadic groups in the area.

"The number of weapons in the area is making such encounters increasingly lethal as nomadic communities now have to travel hundreds of kilometres in search of pasture," he said.

U.N. officials also say that lawlessness in areas of the Horn of Africa is making it harder to deliver food aid.

Number of people malnourished (2001-2003)	36 million (The State of Food Insecurity in the World 2006, U.N. Food and Agriculture Organisation-FAO)
Proportion of malnourished in total population (2001-2003)	39 percent (The State of Food Insecurity in the World 2006, FAO)
People in need of of food aid	4.3 million (WFP)