Remanonjona Feroce founded the village of Anjamahavelo – meaning At the Lucky Baobab – in Madagascar a generation ago. With memories of a flood still fresh, he chose a spot far from the nearest river. He cleared the wild forest and sacrificed a sheep in the hope that it would make the owls, lemurs and snakes go away.

"Animals can't live together with little children and young girls," explained Feroce, an 85-year-old great-grandfather. "They don't want snakes to be here because they have bad spirits. They strangle children by curling around the neck. Owls are bad birds. If one hoots, it means somebody will die."

The animals did go away, but so did the luck of Anjamahavelo, a cluster of wooden houses. Southern Madagascar has had three years of crop failure in five years, resulting in chronic hunger for tens of thousands of families and soaring rates of malnutrition, stunted growth and death among children.

Three forces are combining with deadly effect on the Indian Ocean island, which is incalculably rich in wildlife but impoverished in basic infrastructure. Climate change is widely blamed for playing havoc with the seasons and destroying agricultural harvests. This is exacerbated by local deforestation, which has altered the microclimate and reduced rainfall.

Finally, a bloody political coup earlier this year paralysed essential services and led to the crippling suspension of several foreign aid programmes. The UN says that nearly half of households in the south have severe food shortages.

To feed her five children in Anjamahavelo, Tinalisy – her only name – works as a prostitute at the end of each month, when the local men, mostly in the police, have been paid. The unmarried 27-year-old has slept with men for sex since she was 17. "If the men don't want to marry, that is not really a problem. We have to survive."

Tinalisy says her 20-month-old daughter, Vany Lentine, suffers a fever each evening. "We eat once or twice a day – always cassava. I'm worried but what I can do? There is no money. People here are unhappy because their children do not eat. There is nothing to be happy about."

Other villagers say that the fierce competition for dwindling resources has led to lawlessness and violence. Valiotaky, 56, the village chief, supplies an explanation for the drought. "When we plant trees we don't have rain and nothing grows," he said. "I think God is angry. Young people don't respect the traditions."

Perversely, people in the south are so starved of water that they crave the increasingly fierce cyclones that pound the north three times a year. Two separate dry seasons have progressively expanded until they meet to form one long hot season, hitting crops such as maize, manioc and sweet potato.

Tovoheryzo Raobijaona, director of a food insecurity early warning system in nearby Ambovombe, said: "Before, people spoke about the cycle of drought every 10 years. Now it's every five years, or every three years. After a bad year like 2009, people need two to three years to get back to standard."

Unicef, the UN's children's agency, said that in the past six months 8,632 children had been treated for severe acute malnutrition in three southern regions – more than double the expected number. The UN's World Food Programme (WFP) warns that 150,000 children could be affected this year.

There are reports of people resorting to eating lemurs and turtles, even though these are culturally taboo. They have also resumed cutting down trees for firewood or to make space for rice fields, inadvertently adding to the drought problem by reducing the capacity of forests to capture water that will evaporate into clouds and become rain.

The added impact of global climate change is difficult to quantify. The World Bank says that only one thing is certain: in the past half century Madagascar has seen a 10% increase in temperature and 10% decrease in rainfall. Experts say it is not a question of whether this trend will continue, but by how much.

Silvia Caruso, deputy country director of the WFP, said: "Environmental degradation and climate change are building on each other. The results are dramatic in Madagascar."

This has been compounded by political instability. In March Andry Rajoelina, a city mayor, businessman and former DJ, seized power from president Marc Ravalomanana after clashes that left dozens dead. The fallout has been political deadlock, economic downturn, job losses, price inflation, collapsing public services, a flight of investors and international sanctions on a country that relies on foreign aid for half its budget.

Caruso added: "The coup has paralysed services that we need to work with in the provinces. It has made the response to drought more complex. We had to fill the gaps at regional level."

Bruno Maes, Unicef's representative for Madagascar, described the coup as "a disaster for children", adding: "Madagascar was on the road to take-off. They understood it was time to make reforms in health and education, so that all children can have access. Now all this is frozen. Nothing is moving."

Unicef has provided medicine and training to all regional health clinics for acute malnutrition cases, supported food distribution and worked to improve sanitation. The WFP has begun programmes to provide school meals to 215,000 children, help 8,000 households mitigate against environmental change and supply supplementary feeding to around 70,000 children under two and pregnant and lactating women.

Maes said Unicef was also negotiating with the World Bank to directly administer money earmarked for teachers' salaries. "Children's rights should be addressed in any situation – whatever the crisis."

Case-study: 'Lack of food is eating us up'

Zanasoa Relais Anjado, 38, has 11 children. Her husband, a former plantation worker, is unemployed. They live in Anjado village in southern Madagascar.

"Lack of food is eating us up every day. We often go through very hard moments – in the most difficult we ate only tamarinds [fruit] mixed with ashes. We were hungry and tired and had to beg for something to eat. We were like famine victims … I have 11 children and I don't know how to feed them. Sometimes we have one meal a day, sometimes two. One of my children was sick. He managed to survive and recover, but I know people in the community who are still very weak. The river is 5km from here and we walk for hours to get there … With rainwater we would cook food and diversify agriculture. We'd plant cabbages, green leaves, corn and beans. What we planted so far dried and failed … It will be really difficult and we will suffer. That is why I am asking the government for help, directly and immediately. Without it, we risk dying here. I don't care about the political situation in the country. The only thing that concerns me is that I'm eating."