Repeated failed crops caused by worsening drought have forced Christine Mwenda, a small--scale farmer in Zambia's central Mumbwa region, to do what was previously unthinkable.

Since 2014, the 37--year--old has been selling sex in Zambia's capital Lusaka. The pay is better than growing maize, she said, and gives her a proper chance to feed her four children.

"On average I make close to 500 kwacha ($0.70) on a good day," said Mwenda, who agreed to be interviewed on condition that her real name was not used.

"This is the kind of money I could only make (once) in a year from farming," she said, explaining that once the cost of fertiliser, labour, transport and seeds was deducted, she was left with very little money from her harvest.

Like millions of Zambians, Mwenda has been struggling with soaring food bills and power shortages caused by prolonged drought exacerbated this year by El Nino, a warming of the Pacific Ocean's surface leading to hot, dry conditions.

For many small--scale and subsistence farmers in the landlocked southern African country, longer spells of drought and increasingly erratic rains are becoming far more frequent.

The changing climate, combined with costly fertiliser and seeds, means agriculture is becoming less attractive for many.

"These days when you grow maize you are not sure about the yield. Most of the time you find that the crops end up drying and you only harvest just enough to eat as a family," Mwenda told the Thomson Reuters Foundation.

"Meanwhile we need to send our children to school."

HIV risk

About 54 per cent of Zambia's 16 million people were living in poverty in 2015 --most of them women, according to Central Statistical Office data released in April.

Much of Zambia's extreme poverty is concentrated in rural areas. According to a 2014 United Nations Development Programme (UNDP) report, extreme poverty is estimated to be four times higher in rural areas than urban centres.

The situation in the copper--producing country has not been helped by a drop in the kwacha against the dollar since April, as a result of depressed global commodity prices.

The hardships have caused more and more people to migrate from rural parts to cities such as Lusaka, Kitwe, Livingstone and Chipata. Others have moved to border towns.

Lucy Bwalya, an academic at Cavendish University in Lusaka, said many women turn up in cities hoping to become traders, hawking clothes or groceries.

But a rising number turn to prostitution instead - risking arrest, violence and sexually transmitted diseases.

"Prostitution is the easiest way out and these women end up risking diseases such as HIV and Aids," said Bwalya, a former programmes manager for Tasintha, a charity working with 

sex workers.

According to the 2013/14 demographic and health survey, the HIV prevalence rate among Zambians aged between 15 and 49 was 13 per cent, compared to 16 per cent in 2001/2.

Climate--resistant crops

To encourage more women to stay on their farms, Zambian charity Enviro Green has been teaching them to grow climate resistant crops such as sorghum, which require less water than the traditional staple, maize.

"We are generally concerned with this rural--urban migration of people, especially women who are ending up in sex work," said Enviro Green executive director, Martha Simukonde.

The women farmers are also taught farming techniques to conserve soil and water to minimise erosion and water runoff.

"We always teach them to plant their crops early so that with the early rains they can germinate. Even when the rains go, the crops once planted early have a chance to grow," Simukonde said.

For some women, however, these efforts come too late.

Women in Law and Development in Southern Africa (WILDAF), a women's rights advocacy group, said the government should do more to address rural-urban migration.

"There is need for the government to seriously put in place policies that will reverse this trend where women are coming to urban areas to engage in sex work, which is exposing these women to HIV and Aids," said WILDAF programmes officer Charles Sibeene.