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Southern Africa: Climate Threat to Zambezi Basin
AfricaFocus Bulletin
Oct 3, 2012 (121003)
(Reposted from sources cited below)
Editor's Note
According to a new study released in September, "There will
be a significant reduction in the amount of water flowing
through the [Zambezi] river system, affecting all eight
countries it passes through. The water that feeds the river
is expected to decrease by between 26 percent and 40 percent
in another four decades. But when the rains do fall, they
will be more intense, triggering more extreme floods."
Nevertheless, says the author of the study, planning for
existing and new dams does not yet take account of the
impact of climate change in reducing power generation and
capacity for flood control.
The study, A Risky Trip for Southern African Hydro, was
conducted for the NGO, International Rivers by Richard
Beilfuss, a hydrologist and environmentalist who teaches at
the University of Wisconsin-Madison College of Engineering
in the US and the University of Eduardo Mondlane in
Mozambique. Beilfuss says the region - and the rest of
Africa as well - must reconsider the construction of massive
hydropower dams and rethink their use as a flood management
tool, especially as floods are expected to worsen with
climate change.
This AfricaFocus Bulletin contains a news report on the
study and excerpts from the introduction and the
executive summary. The full study is available at
http://www.internationalrivers.org
For previous AfricaFocus Bulletins on climate and
environmental issues, visit http://www.africafocus.org/envexp.php
++++++++++++++++++++++end editor's note+++++++++++++++++
Southern Africa: New Urgency to Rethink Dam Projects
26 September 2012
http://allafrica.com/stories/201209270543.html
UN Integrated Regional Information Networks
http://www.irinnews.org
Johannesburg - The massive hydropower dams built on the
Zambezi River, the largest river system in Southern Africa,
not only supply power to major economies in the region but
also help mitigate annual floods. But as electricity demands
grow and rising global temperatures affect rainfall
patterns, the dams will be unable to meet energy needs or
control floods, warns a new study.
The study, A Risky Trip for Southern African Hydro, was
conducted for the NGO, International Rivers by Richard
Beilfuss, a hydrologist and environmentalist who teaches at
the University of Wisconsin-Madison College of Engineering
in the US and the University of Eduardo Mondlane in
Mozambique. Beilfuss says the region - and the rest of
Africa as well - must reconsider the construction of massive
hydropower dams and rethink their use as a flood management
tool, especially as floods are expected to worsen with
climate change.
"Large dams are being built or proposed, typically without
analysis of the risks from hydrological variability that are
already a hallmark of African weather patterns, much less
the medium- and long-term impacts expected from climate
change," Beilfuss noted in the report. "Likewise, ecosystem
services are rarely given much weight in the energy-planning
process."
Extreme floods expected
The report uses the Zambezi basin as a case study to inform
governments planning to establish new hydropower plants.
Assessing climate change impact studies conducted on the
Zambezi River Basin, Beilfuss said the Zambezi is expected
to experience "drier and more prolonged drought periods".
Over the next century, rainfall is expected to decrease by
between 10 and 15 percent over the basin, according to
several studies cited by the Intergovernmental Panel on
Climate Change. There will be a significant reduction in the
amount of water flowing through the river system, affecting
all eight countries it passes through. The water that feeds
the river is expected to decrease by between 26 percent and
40 percent in another four decades, the study observed.
But when the rains do fall, they will be more intense,
triggering more extreme floods.
No major dams are currently under construction on the
Zambezi, Beilfuss told IRIN, but two large dams have been
proposed: Batoka Dam on the Middle Zambezi and Mphanda Nkuwa
Dam on the Lower Zambezi. "Batoka is politically and
financially complex because it must be a joint project
between Zambia and Zimbabwe," Beilfus said. "Mphanda is
entirely within Mozambique and is in very advanced stages of
preparation with a timeline for construction."
There has been considerable opposition to Mphanda Nkuwa,
which environmentalists warn could displace several thousand
people. Much of the anxiety over its construction is fuelled
by the experience of the Cahora Bassa Dam in Mozambique,
which has been widely cited as an environmental catastrophe
since its construction in the early 1970s by the former
Portuguese colonial government.
"None of these projects, current or proposed, has seriously
incorporated considerations of climate change into project
design or operation," noted Beilfuss.
Guido Van Langenhove, who heads Namibia's Hydrological
Services Department, agreed with the concerns raised by
Beilfuss and said, "Our dams cannot handle one-in-a-hundredyear
[extreme] flood events. They cannot handle the sheer
volume of water that might be involved. We have to even
consider how to fortify our existing structures."
Disasters
Recent floods and their impact on the existing dams offer a
possible view of future disasters. In 2007, heavy rains over
the Zambezi threatened the dam structure, forcing the
authorities to open the sluice gates of the Cahora Bassa
Dam, affecting up to half a million people [some displaced,
but others had crops destroyed etc].
Large dams are being built or proposed, typically without
analysis of the risks from hydrological variability that are
already a hallmark of African weather patterns, much less
the medium- and long-term impacts expected from climate
change
In a case study on the floods and cyclones that struck
Mozambique that year, the Overseas Development Institute
warned that the two biggest dams on the Zambezi, Cahora
Bassa and Zambia's Kariba, "do not have the spill-way
capacity to cope with the very large floods that occur on
the river every five to 10 years. At best, the dam operators
can slow down the sudden rise in water levels by phasing the
spillage of water over a period of a few days, which gives
the people living downstream a little more time to evacuate
their homes."
Hydrologists in Southern Africa have been calling for a
reconsideration of dam planning for years. In 2001, Bryan
Davies, an ecologist and a Zambezi river expert, conducted
an assessment of the Cahora Bassa and told IRIN, "one of
these days there will be a cyclonic event" that the full
dams would be unable to cope with.
Part of the problem is that the Zambezi River Basin in
Mozambique is a naturally occurring flood plain. In the
past, human habitation patterns took flooding into account.
When the waters subsided, people would move in to plant in
the rich soils, and shift to higher ground when the floods
returned, but since the construction of Cahora Bassa,
communities have settled much closer to the river, making
them more vulnerable, Davies warned.
Van Langenhove, the Namibian official, said people
mistakenly believe that the construction of a dam means they
will safe from flooding, and so tend to settle close to
dams. "Should an extreme event take place, there would be a
huge disaster," he said.
Finding alternatives
Beilfuss suggested using hydropower dams to produce
electricity only and not to store flood water. "Many
hydropower projects are justified on the basis of providing
flood control in addition to energy generation. However,
allowing for flood storage means the reservoir must be drawn
down to provide flood capture space at the very time that
this water is most needed to supply energy".
The vast natural flood plains of the Zambezi should be
allowed to flood while ensuring people do not settle in
those areas, he said. "This will allow for regeneration of
the floodplains systems for wildlife and fisheries and
agriculture, and also will reduce the impact of extreme
floods - which already occur in the basin as it is - on
people and property.
"By removing people from flood-prone areas - in accordance
with Mozambique and Zambia law, by the way - it becomes
especially important to restore modest annual high flows in
the basin so that people can secure their livelihoods from
fisheries and agriculture," he told IRIN by email.
Beilfuss also suggested that countries in the region improve
existing hydropower capacity rather than investing in new
infrastructure. "Adding new or more efficient turbines is
almost always much lower-impact than building new dams."
Countries should also consider alternative sources of energy
generation.
In 2011, the eight countries through which the Zambezi flows
set up the Zambezi Watercourse Commission (ZAMCOM) to manage
the river. Though still a new body, "ZAMCOM is a very
important step forward for the integrated development and
water conservation in the Zambezi River Basin," Beifluss
said. "In particular, the ZAMCOM structure offers the
potential to strategically address river development,
including hydropower, on a basin-wide level rather than a
country-by-country level."
Americo Jose Ubisse, secretary general of the Mozambique Red
Cross, has been involved in flood relief operations in
Mozambique for many years. He told IRIN in an email that, in
the past, issues related to the "environment, climate change
and their future humanitarian consequences were deeply
undermined... The added value that is coming with these
scientific studies must be taken into consideration.
Undermining [scientific studies]... can be a big mistake,
not only for the future of economic investment but also for
the future of humanitarian sustainability."
A Risky Climate for Southern African Hydro
Assessing Hydrological Risks and Consequences for Zambezi
River Basin Dams
By Dr. Richard Beilfuss
Published in September 2012 by International Rivers
http://www.internationalrivers.org
Part 1: Introduction
Climate Change In Africa
In the coming decades, billions of people, particularly
those in developing countries, will face shortages of water
and food and greater risks to health and life as a result of
climate change. ...
Africa is already a continent under pressure from climate
stresses and is highly vulnerable to the impacts of climate
change. Many areas in Africa are recognized as having
climates that are among the most variable in the world on
seasonal and decadal time scales. Serious floods and
droughts can occur in the same area within months of each
other. These events can lead to famine and widespread
disruption of socio-economic well-being. An estimated onethird
of African people already live in drought-prone areas
and 220 million are exposed to drought each year. Many
factors contribute to and compound the impacts of current
climate variability in Africa. These include poverty, weak
institutions, limited infrastructure, lack of technology and
information, low levels of primary education and health
care, poor access to resources, and armed conflicts. The
overexploitation of land and water resources, increases in
population, desertification and land degradation pose
additional threats (UNDP 2006).
Climate change forecasts for Africa predict that the
continent's weather patterns will become more variable, and
extreme weather events are expected to be more frequent and
severe, with increasing risk to health and life (McMichael
et al. 2006).This includes increasing risk of drought and
flooding in new areas (Few et al. 2004), and inundation due
to sea-level rise in the continent's coastal areas (Nicholls
2004). Within the next 50 years, the number of people facing
water stress will increase dramatically (Arnell 2004).
Climate change will be an added stress to already threatened
species and ecosystems in Africa, and is likely to trigger
species migration and habitat reduction on an unprecedented
scale. Up to 50% of Africa's total biodiversity presently is
at risk due to land-use conversion for settlement and
agriculture, deforestation, pollution, poaching, civil war,
population growth, and the introduction of exotic species
(Boko et al. 2007). Freshwater ecosystems, especially river
systems, have experienced rapid degradation due to the past
century of water resources development, and are particularly
vulnerable to the added effects of climate change (Palmer et
al. 2008; Pittock et al. 2008;Vorosmarty et al. 2010).
Hydropower Development, River Systems, and Climate Change
Across the continent, African leaders face an enormous and
growing demand for energy, and the added challenge of
establishing sustainable energy systems in the face of
climate change. Numerous large dams are being built or
proposed to meet Africa's long-term power supply needs.
Development planners argue that large hydropower dams are a
least-cost, indigenous power supply, and note that less than
10% of the region's hydropower potential has been developed.
Hydropower is increasingly promoted as a source of energy
with low emissions of greenhouse gases, with a production
capacity at a scale necessary to meet pressing energy
demands with current technology (Pittock 2010).
However, Sub-Saharan Africa (excluding South Africa) is
already 60% dependent on hydropower for its power supply,
and many individual countries are much more dependent.
Recurring drought is commonly acknowledged as a leading
contributor to power shortages in numerous hydro-dependent
countries. Drought-induced power shortages come at great
economic cost to local economies, and add to the perception
that African economies are risky places to do business.
Kenya, for example, experienced a 25% reduction in
hydropower capacity during the 2000 drought, resulting in
an estimated 1.5% reduction in GDP valued at $442 million
(Stiftung 2010). Expanding the hydrological hydropower in
Africa's energy sector would increase dependence of African
power grids on rainfall.
Also at stake (but rarely given much weight in the energyplanning
process) is the wealth of ecological services
provided by river systems that sustain life on earth.
Freshwater ecosystems and species are among the most highly
threatened in the world. Hydropower dams block fish
migrations, inundate upstream habitats, and displace human
communities. Downstream, the modification of water flow
regimes caused by dams is one of the primary causes of the
degradation of freshwater ecosystems worldwide (Richter et
al. 1997). ... Extreme fluctuations in flow resulting from
peak-power production also stress fish and aquatic
ecosystems. In addition to changes in the flow regime, dams
can heavily modify water temperatures and the downstream
transport of sediment,further affecting river ecosystems.
All of these environmental impacts can have serious
implications for downstream plant and animal communities, as
well as human communities dependent upon the goods and
services provided by properly functioning river ecosystems.
Climate change further exacerbates these challenges. The
IPCC technical group on climate change and water (Bates et
al. 2008) raised concern that climate change will affect the
functional operation of existing water infrastructure,
including hydropower, and water management practices. Large
hydropower projects are highly vulnerable to future changes
in precipitation and streamflow. ...
African energy planning is occurring without the benefit of
proper analysis of the risks to large dams' viability from
hydrological variability that is already a hallmark of
African weather patterns, much less the medium- and longterm
impacts posed by climate change. With regard to climate
change, two risks are routinely overlooked in energy
planning at both the sectoral and project levels. First,
historical hydrological patterns (on which hydropower
operation and project viability are routinely based) are
becoming unreliable for predicting future hydrological
patterns. Second, the current course of dam building in
Africa is not being evaluated with respect to the impact of
dam-induced hydrological changes on the ability of rural
populations to adapt to climate change.
How can the risks of hydrological uncertainty on African
energy portfolios be assessed and integrated into sectoral
and project-level decision-making? What policy changes
should governments adopt to address the risks of hydropower
dependency in national and regional power sectors, in light
of such hydrological uncertainty? This report examines risk
and uncertainty related to hydropower development and
climate change in Southern Africa, focusing on the Zambezi
River Basin as a case study.
The Zambezi River Basin
More than a decade ago, the IPCC (2001) categorized the
Zambezi as the river basin exhibiting the "worst" potential
effects of climate change among eleven major African basins,
due to the resonating effect of increase in temperature and
decrease in rainfall on potential evaporation and runoff.
...
The Zambezi River Basin is the largest in Southern Africa,
with a total drainage area of approximately 1.4 million km2.
The Zambezi mainstem, with a total length of 2,574 km,
originates in the Kalene Hills in northwest Zambia at an
altitude of 1,500m and flows south and eastwards to the
Indian Ocean. The river has three distinct stretches: the
Upper Zambezi from its source to Victoria Falls, the Middle
Zambezi from Victoria Falls to Cahora Bassa Gorge, and the
Lower Zambezi from Cahora Bassa to the Zambezi Delta.
Zambezi waters are critical to sustainable economic growth
and poverty reduction in the region. In addition to meeting
the basic needs of some 30 million people and sustaining a
rich and diverse natural environment, the river plays a
central role in the economies of eight riparian countries -
Angola, Botswana, Malawi, Mozambique, Namibia,Tanzania,
Zambia, and Zimbabwe. The Zambezi provides important
environmental goods and services to the region and is
essential to regional food security and hydropower
production.
Home to a rich biological diversity and some of the densest
concentrations of wildlife in the world, the Zambezi River
Basin features several of Africa's finest national parks.
The Middle Zambezi Valley is a UNESCO Biosphere Reserve.
Eight Zambezi Basin floodplains are designated as Wetlands
of International Importance under the Ramsar Convention,
including the Barotse Plain, Busanga Plains, Kafue Flats,
Mana Pools (also a World Heritage Site), Lower Zambezi
National Park, Elephant Marsh,and the Zambezi Delta. The
Zambezi features the most important concentrations in Africa
of endangered wattled cranes, African elephant, African
buffalo, and many other species.
The Zambezi River Basin currently has approximately 5,000 MW
of installed hydropower generation capacity. Major
hydropower dams include Kariba and Cahora Bassa Dams on the
mainstem Zambezi River, Itezhi-Tezhi and Kafue Gorge Upper
Dam on the Kafue River, and the Kamuzu Barrage that
partially regulates Lake Malawi water levels for downstream
Shire River hydropower production at Nkula Falls,Tedzani,
and Kapichira Stage I hydropower dams. An additional 13,000
MW of hydropower potential has been identified (World Bank
2010). None of the Zambezi hydropower development projects,
current or proposed, has seriously incorporated
considerations of climate change into project design or
operation, despite a history of economically devastating
droughts and floods that are predicted to become more
commonplace in the future.
Numerous studies have addressed the socioeconomic and
ecological impacts of existing hydropower development in the
Zambezi River Basin. Hydropower dams have resulted in
significant shifts in the timing, magnitude, duration, and
frequency of annual flood pulses and low-flow events on the
Zambezi (Beilfuss 2002). Deleterious ecological changes
associated with this hydrological degradation include downcutting
of the Zambezi channel below the adjacent floodplain
and reduced floodplain water table, invasion of woody
savanna and thicket vegetation into open grassland and
wetland, abandonment of former distributary channels,
displacement of freshwater grassland species with salttolerant
grassland species, degradation of coastal
mangroves, and reduction in breeding and feeding grounds for
endemic and threatened mammal and waterbird species (Tinley
1975, Rees 1978a&b, Handlos and Williams 1985, Beilfuss et
al. 2000, Davies et al. 2001, Bento et al. 2007). Socioeconomic
concerns include reductions in freshwater and prawn
fisheries, floodplain and riverbank agriculture, floodplain
water supply, and wildlife carrying capacity for tourism and
trophy hunting (SWECO 1983, Bolton 1986, Sushka and Napica
1986, Anderson et al. 1990, Gammelsr?d 1992, Beilfuss et al.
2002, Tha and Seager 2008). Many of these concerns will be
exacerbated by the drier, and more drought- and flood-prone
conditions resulting from climate change in the Zambezi
Basin.
...
Executive Summary
...
Hydrological Variability and Hydropower in the Zambezi River
Basin
An understanding of the hydrological variability in the
Zambezi River Basin is fundamental to assessing the risks,
uncertainties, and consequences of hydro-dependent power
systems.
The Zambezi River Basin has one of the most variable
climates of any major river basin in the world, with an
extreme range of conditions across the catchment and through
time. Average annual rainfall varies from more than 1,600 mm
per year in some far northern highland areas to less than
550 mm per year in the water-stressed southern portion of
the basin.
Runoff is highly variable across the basin, and from year to
year. The entire Zambezi River Basin is highly susceptible
to extreme droughts (often multi-year droughts) and floods
that occur nearly every decade. Droughts have considerable
impact on river flows and hydropower production in the
basin. For example, during the severe 1991/92 drought,
reduced hydropower generation resulted in an estimated
US$102 million reduction in GDP, $36 million reduction in
export earnings, and the loss of 3,000 jobs. Extreme floods
have resulted in considerable loss of life, social
disruptions, and extensive economic damage. Hydropower
operators and river basin managers face a chronic challenge
of balancing trade-offs between maintaining high reservoir
levels for maximum power production and ensuring adequate
reservoir storage volume for incoming floods.
The natural variability of Zambezi River flows is highly
modified by large dams, particularly Kariba and Cahora Bassa
dams on the mainstem, as well as Itezhi-Tezhi and Kafue
Gorge Upper dams on the Kafue River tributary. Zambezi
hydropower dams have profoundly altered the hydrological
conditions that are most important for downstream
livelihoods and biodiversity, especially the timing,
magnitude, duration, and frequency of seasonal flood pulses.
More than 11% of the mean annual flow of the Zambezi
evaporates from large reservoirs associated with hydropower
dams. These water losses increase the risk of shortfalls in
power generation, and significantly impact downstream
ecosystem functions.
With the dams in place, overbank flood pulses now occur only
during major floods in the basin, and are of inadequate
volume and duration to sustain healthy functioning
floodplain systems that are of global importance, such as
Kafue Flats, Mana Pools, and the Zambezi Delta. High flood
pulses, when they occur, are often mistimed - they are
generated during emergency flood releases or the late dry
season in response to required drawdown releases. Dry season
flood-recession, essential for river-dependent agriculture,
fisheries, and wildlife, is replaced by constant dry-season
flows generated from hydropower turbine outflows. The
economic impact of the loss of these and other ecosystem
services is an important factor in the overall financial
risk of hydropower development, especially in a changing
climate.
Climate Risks in the Zambezi Basin
The Intergovernmental Panel on Climate Change (IPCC) has
categorized the Zambezi as the river basin exhibiting the
"worst" potential effects of climate change among 11 major
African basins, due to the resonating effect of increase in
temperature and decrease in rainfall. The Zambezi runoff is
highly sensitive to variations in climate, as small changes
in rainfall produce large changes in runoff. Over the next
century, climate change is expected to increase this
variability, and the vulnerability of the basin - and its
hydropower dams - to these changes.
Under future climate scenarios, a hydropower dam based on
the past century's record of flows is unlikely to deliver
the expected services over its lifetime.
The future picture for Southern Africa's climate is
increasingly clear, based on observed trends over the past
century and increasing confidence in the range of climate
change scenarios developed. Overall, the Zambezi will
experience drier and more prolonged drought periods, and
more extreme floods. ...
Hydropower's Climate Risks
These staggering climate change predictions, based on the
average (not extreme case) of many climate models, have
profound implications for future hydropower in the Zambezi
River Basin. Climate change has the potential to affect
hydropower operations in at least five important ways:
- Reduced reservoir inflows, due to decreased basin runoff
and more frequent and prolonged drought conditions, will
reduce overall power output.
- Increased extreme flooding events, due to higher rainfall
intensity and more frequent cyclones, will increase the risk
of worse flood impacts from uncontrolled releases, and risks
to dam safety.
- A delayed onset of the rainy season could result in less
predictable power production and more uncertainty and
complications in using reservoirs for flood
management.
- Increased surface-water evaporation could reduce power
production.
- Increased sediment load to reservoirs, resulting from
higher rainfall intensity and corresponding erosion, will
lead to a decrease in reservoir capacity and greater
difficulty in managing floods.
Numerous studies have indicated that hydropower economics
are sensitive to changes in precipitation and runoff. Most
hydropower projects are designed on the basis of recent
climate history and the assumption that future hydrological
patterns will follow historic patterns. However, this notion
that hydrological systems will remain "stationary" in the
future (and thereby predictable for the design and operation
of hydropower schemes) is no longer valid. Under future
climate scenarios,a hydropower station based on the past
century's record of flows is unlikely to deliver the
expected services over its lifetime. It is likely to be
over-designed relative to expected future water balances and
droughts, and under-designed relative to extreme inflow
events. Extreme flooding events, a natural feature of the
Zambezi River system, have become more costly downstream
since the construction of large dams, and will be
exacerbated by climate change. The financial and social
impact of a major dam failure in the Zambezi River Basin
would be nothing short of catastrophic. ...
Ecosystem Services Undervalued
The wealth of ecological services provided by river systems
that sustain life on earth are rarely given much weight in
the energy planning process. The current course of dam
building in Africa is not being evaluated with respect to
the impact of dam-induced hydrological changes on the
ability of rural populations to adapt to new flow
regimes,much less on their ability to adapt to climate
change's impacts more generally. Ecosystem services are of
critical importance for adaptation to climate change. ...
The value of the ecosystem services threatened by hydropower
development in the Zambezi River system is astonishing. A
recent economic valuation study estimates that the annual
total value of river-dependent ecosystem services in the
Zambezi Delta is between US$930 million and $1.6 billion.
Agriculture, fisheries, livestock, tourism, and domestic
water supply are all affected. Cumulatively, the economic
value of water for downstream ecosystem services exceeds the
value of water for strict hydropower production - even
without valuation of biodiversity and cultural uses of the
river system.
AfricaFocus Bulletin is an independent electronic
publication providing reposted commentary and analysis on
African issues, with a particular focus on U.S. and
international policies. AfricaFocus Bulletin is edited by
William Minter.
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