Soaring temperatures and erratic rains brought on by a changing climate may radically alter water flows in the world’s major river basins, including the Limpopo in southern Africa, forcing people to give up farming in some areas, says a new study.
The study - part of a five-year research project on four continents, the first to take a close look at 10 river basins - is based on data from 17 climate models used by the Intergovernmental Panel on Climate Change (IPCC) to examine the potential effect of changing temperatures and rainfall patterns on the water flows in rivers from now until 2050.
Climate models cannot predict how rainfall patterns will behave in future with a high degree of certainty, said Mark Mulligan, a climate change scientist at King’s College, London, and lead author of the study.
“What we do know is that we cannot be confident about hydrological stability. Some rivers could become wetter and then drier, or vice versa. The key message to countries is: ‘Become more adaptable’.”
There are problems with the science when it comes to making projections of climate change impact on rivers, but the study expects that all African river basins will be water-stressed by increased rates of evapo-transpiration as temperatures rise, but is uncertain about how gains in rainfall may offset that impact.
In Asia the seasonality of changes in rainfall and temperature - which affects how rivers behave in the wet or dry season - will be critical, especially in wet basins like the Mekong.
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Mulligan drew parallels with the uncertainty of the current financial crisis, pointing out that unprepared institutions and experts were responding in crisis mode. He said their findings on the impact of climate change on river basins indicate that the world faces an uncertain future regarding water, and the impact was unpredictable.
“So you cannot even draw up an adaptation strategy, as we are not certain about what we need to adapt to… the goal post will keep changing,” he said. A framework is needed to plan a strategy for the better management of water, and make countries and people more resilient.
Besides climate data, the scientists also factored in population growth and poverty levels. The gross domestic product (GDP) in the Nile, Niger and Limpopo river basins is low, the study noted, with few options for resilience to climate change, except for the Nile, whose significant potential to store water is being developed.
The study was conducted by scientists from the Challenge Program on Water and Food of the Consultative Group on International Agricultural Research. Its findings were released at the three-day Third International Forum on Water and Food outside Pretoria, South Africa, which began on 14 November.
Here are some of the key findings concerning the impact on food security, with suggested steps to become more adaptable:
Ganges (Bangladesh, India, Nepal, Bhutan): High temperatures may increase or decrease productivity, depending on the impact on evapo-transpiration. The basin is highly vulnerable because of the number of people who live in the basin (400 million), dependence on agriculture and unsustainable water use.
Steps: Store winter flows in dams and manage groundwater recharge to use for agriculture during dry season
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Karkheh (western Iran): Strong warming in this already highly seasonal basin with hot summers and low rainfall may affect the food security of the population in this major river system.
Steps: Try to diversify livelihoods and develop industry. Store water and rely on irrigation where self-sufficiency is critical.
Limpopo (South Africa, Mozambique, Botswana, Zimbabwe): Irregular seasonal fluctuations in rainfall and temperatures may affect the lives of at least 14 million people in this basin - for instance, the dry season might get drier, or the wet season may deliver less rain than normal.
Steps: Diversify livelihoods to lessen dependence on agriculture. Harvest and store rainwater.
Mekong (China, Myanmar, Laos, Cambodia, Thailand, Vietnam): The basin is not likely to experience strong warming or greatly altered rainfall patterns, but a least 60 million people may be affected by flooding and sea level rise.
Steps: Better management of storm water flow, water quality and sanitation; and diversification of livelihoods.
Niger (Guinea, Cote d’Ivoire, Mali, Burkina Faso, Algeria, Benin, Niger, Chad, Cameron, Nigeria); The impact on the food security of the roughly 100 million people living here varies from north to south in this very hot basin, which has experienced drought since the 1970s.
The climate modelling results are uncertain and contradictory, but a warming trend is indicated, with an increase in variability and extreme events, a later start to the rainy season, more dry spells, and more rain in the central parts of west Africa and less in the far west.
Steps: Harvest and store rainwater; exploit groundwater; train farmers in good agricultural practices such as use of fertiliser and drought-tolerant crops; provide access to financial services and markets.
Nile (White Nile: Uganda, Sudan, Egypt; Blue Nile: Ethiopia, Eritrea, Democratic Republic of Congo, Kenya, Tanzania, Rwanda and Burundi): A World Bank estimate puts the population in the basin of the world’s longest river at about 150 million. The impact on food security could vary from north to south, but if increased evapo-transpiration is offset by higher rainfall there may be no impact.
Steps: Rainfall shocks can be lessened by harvesting rainwater, and the seasonal migration of livestock.
Volta (Burkina Faso, Ghana, Togo, Benin, Mali and Cote d’ Ivoire): There could be an improvement in some areas, with a possible significant increase in rainfall. The team of scientists studying the basin reported that agricultural production in Benin could drop by between 10 and 20 percent; while a slight increase in rainfall in Burkina Faso could benefit cotton production. In Ghana, where rainfall might decrease, there could be a considerable rise in demand for water for irrigation.
Steps: Harvest and store rainwater for irrigation during the dry season.