The World Water Week in Stockholm this month is a major fixture in every water policymaker's diary these days. This year's event, earlier this month, focused on water cooperation – an issue of increasing importance to the CGIAR Research Program on Water, Land and Ecosystems (WLE) as local water conflicts bubble up and threaten international relations. Of recent interest has been the Zambezi River Basin, where WLE plans to expand its focus in 2014.

Zambezi River. Photo Credit: Global Water Partnership on Flickr Zambezi River. Photo Credit: Global Water Partnership on Flickr

Here we go again. It sounds like a repeat of the diplomatic debacle on the Mekong, where the influence of the intergovernmental Mekong Basin Commission to manage the river is hobbled by its absence of the biggest and most upstream country on the river – China.

This time we are in Africa, where the major river of southern Africa, the Zambezi, two years ago got a basin body, the Zambezi Watercourse Commission (ZamCom). But Zambia, the country where the river rises and which houses almost half of the river’s catchment area, is the only country not to join.

Growing unease

This could mean big trouble, as delegates heard at this month's Stockholm World Water Week, where the main theme was international water cooperation. While delegates could report guarded progress on a number of contested rivers – notably the River Jordan, where Israel has begun returning some flow – there was growing unease about the Zambezi and its millions of water users, especially poor farmers and fishers.

On the face of it, this might sound absurd. While the Zambezi and its tributaries pass through eight countries, the river basin appears to have water to spare. Unlike the Nile to the north, there is no fight for the last drop. Right now, only a fifth of the Zambezi's average annual flow of more than 100 cubic kilometres is used – most of it evaporating from hydroelectric reservoirs.

If Zambia starts selling the waters of the Zambezi without the permission of its downstream neighbours, there could be serious trouble.

On its upper floodplains, the annual floods still bring rejoicing in anticipation of an abundant harvest. On the Barotse floodplain in western Zambia, the Lozi people celebrate by bearing their king on a barge to higher ground during their Kuomboka ceremony.

But downstream the stresses are growing. Hydroelectric dams such as the giant Kariba, on the Zambia-Zimbabwe border, and the Cahora Bassa in Mozambique, hold back wet-season flows, and so delay and enfeeble the flood pulse. This damages ecosystems, fisheries, flood-recession irrigation and wet pastures all the way to the Indian Ocean.

Rich grazing lands have already been damaged by the Itezhi-Tezhi dam on the Kafue Flats in Zambia, where a quarter-million cattle graze in the dry season. The dam has much reduced the seasonal floods that once kept the flats' rich pastures wet, delegates heard from Jasmin Mertens of the African Dams Project, a Zurich-based research initiative on the Zambezi.

There are other stresses. In a recent study, International Water Management Institute (IWMI) hydrologist Matthew McCartney warned that land-use change in the basin could be as damaging to the river as concrete barriers. The basin still has extensive miombo deciduous woodlands, which cover two-thirds of the catchment and represent "one of the largest eco-regions in Africa". The woodlands are major regulators of the river basin's hydrology, to which natural ecosystems are adapted. But as farmers and miners strip them, this function will be lost.

Local tension rises over water stress

Even if the basin as a whole has a lot of water, local catchments may not or suffer from periodic droughts. Local water stress is growing, especially where farmers adopt small-scale irrigation in drought-prone areas such as the Chinyanji Triangle, a large area of the basin on the border between Malawi, Zambia and Mozambique. Research being conducted by IWMI here is finding that water shortages are creating social tensions in local communities.

The danger is that local tensions will become regional flashpoints, the African Dams Project reported in Stockholm. "Population and economic growth, as well as expansion of irrigated agriculture and water transfers are likely to have very important transboundary impacts on water availability," risking serious disputes. The project's study highlighted the risk of Mozambique and Zimbabwe challenging the hydrological hegemony of Zambia's, which uses its power as the upstream nation to "expand its consumptive water use" at their expense.

Hence the concern at Zambia's continued failure to join ZamCom.

Zambia's plan

Zambia is not alone in wanting to exploit the river in a part of Africa that boasts sometimes double-digit economic growth. Politicians, industrialists and financiers here all "see dams as a development driver," said Dinis Juizo, a civil engineer at the Eduardo Mondlane University in Maputo, Mozambique. "New development finance is pouring into the Zambezi basin from China, the BRICS and transnational corporations," agreed Kurt Jensen of the Danish Institute for International Studies in Copenhagen, who compared the Zambezi's future with that of the Mekong today.

Leading the charge is Zambia's plan for a megadam in the Batoka gorge, upstream of the Kariba dam on the main stem of the Zambezi. The $3 billion project has the backing of the African Development Bank and is intended to generate power for the country's fast-expanding industry, based on its copper mines, as well as for export into the emerging international power grid across southern Africa. This is creating downstream concern.

And Zambia's plans for the river may not end with exporting electricity, said Juizo. He warned that escalating water demands in the face of drought and climate change across southern Africa will encourage large-scale transfers of water out of the Zambezi basin altogether – to South Africa and elsewhere. If Zambia starts selling the waters of the Zambezi without the permission of its downstream neighbours, there could be serious trouble.

But none of this makes economic sense. Numerous studies show that collaboration over a basin's water should ultimately deliver more benefits all round. The question now for those keen to defuse such disputes is how to persuade Zambia that it is in its own interests to join ZamCom.