Changes in West African Savanna agriculture in response to growing population and continuing low rainfall doi.org/10.1016/0167-8809(90)90214-X

Agriculture, Ecosystems & Environment, 31(2) (2022) 115-132; doi.org/10.1016/0167-8809(90)90214-X

Changes in West African Savanna agriculture in response to growing population and continuing low rainfall

H. I. D. Fierich and W. A. Stoop

International Crops Research Institute for the Semi-Arid Tropics ICRISAT/UNDP, P.O. Box 1165, Ouagadougou, Burkina Faso

(Accepted 12 September 1989; available online 27 June 2003.)

Abstract

Changes in village farming systems brought about by population growth and continuing low rainfall, are described for the three main agro-ecological zones in Burkina Faso. The toposequential land use and cropping patterns were used as the basis for a model, which describes the long-term ecological degradation from declining proportions of fallow land and over-cropping. The implications of these changes for land tenure systems have also been considered. The result provide a human and ecological setting for th current land degradation problem in the West African savanna and thereby indicate possible directions and priorities for future agricultural research.

https://www.sciencedirect.com/science/article/abs/pii/016788099090214X

Impacts of climate change on hydro-meteorological drought over the Volta Basin, West Africa, by P. G. Oguntunde, B. J. Abiodun & G. Lischeid; https://doi.org/10.1016/j.gloplacha.2017.07.003

Global and Planetary Change, (online July 12, 2017), https://doi.org/10.1016/j.gloplacha.2017.07.003

Impacts of climate change on hydro-meteorological drought over the Volta Basin, West Africa

Philip G. Oguntunde, Batatunde J. Abiodun, and Gunnar Lischeid

Highlights

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We examined the past and future characteristics of drought over Volta River Basin.

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We investigated the coupling between drought and streamflow with wavelets analysis.

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A 2–3 month lead time was found between drought indices and stream flow.

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Drought area extent is projected to increase by 24% to 34% in the future.

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This study may guide policy on strategic and adaptive capacity building in the basin.

Abstract

This study examines the characteristics of drought in the Volta River Basin (VRB), investigates the influence of drought on the streamflow, and projects the impacts of future climate change on the drought. A combination of observation data and regional climate simulations of past and future climates (1970–2013, 2046–2065, and 2081–2100) were analyzed for the study. The Standardized Precipitation Index (SPI) and Standardized Precipitation and Evapotranspiration (SPEI) were used to characterize drought while the Standardized Runoff Index (SRI) were used to quantify runoff. Results of the study show that the historical pattern of drought is generally consistent with previous studies over the Basin and most part of West Africa. RCA ensemble medians (RMED) give realistic simulations of drought characteristics and area extent over the Basin and the sub-catchments in the past climate. Generally, an increase in drought intensity and spatial extent are projected over VRB for SPEI and SPI, but the magnitude of increase is higher with SPEI than with SPI. Drought frequency (events per decade) may be magnified by a factor of 1.2 (2046–2065) to 1.6 (2081–2100) compared to the present day episodes in the basin. The coupling between streamflow and drought episodes was very strong (P < 0.05) for the 1–16-year band before the 1970 but showed strong correlation all through the time series period for the 4–8-years band. Runoff was highly sensitive to precipitation in the VRB and a 2–3 month time lag was found between drought indices and streamflow in the Volta River Basin. Results of this study may guide policymakers in planning how to minimize the negative impacts of future climate change that could have consequences on agriculture, water resources and energy supply.

http://www.sciencedirect.com/science/article/pii/S0921818116305215

Catastrophic mesoscale convective system storms in the western Sahel now three times more likely

Climate change brings more Sahel storms

Climate change is upsetting rainfall patterns and the frequency of flooding in West Africa as it makes the region's Sahel storms three times likelier.

by Tim Radford, Climate News Network, May 7, 2017

LONDON – Climate change has already made a difference to life in the West African Sahel, the arid belt of land stretching from the Atlantic to the Red Sea which separates the Sahara desert from the African savanna. It has made catastrophic storms three times more frequent.

And, according to a new study in the journal Nature, Sahel storms are among the most powerful on the planet. In 2009, one vast downpour deposited 263 mm of rain over Ouagadougou, the capital of Burkina Faso, claiming 8 lives, flooding half the city and forcing 150,000 people out of their homes.

Researchers believe the pattern of thunderstorms known as mesoscale convective systems will increase in frequency as global temperatures rise, as a consequence of increasing levels of carbon dioxide in the atmosphere, in turn driven by worldwide use of fossil fuels as sources of energy.

Mesoscale convective systems are big, bad, and very cold columns of thunderous cloud: up to 16 km high, covering an area of 25,000 square kilometres, and with temperatures at the highest altitude as low as minus 40 °C.

Between 1986 and 2005, Burkina Faso registered floods at a rate of little more than one a year. In the 11 years between 2006 and 2016, it was hit by 55 flood events.

Repeated warnings

Climate scientists have been warning for three decades that global warming will be accompanied by an increase in “extreme” events: in particular drought, flood, heat wave, and tropical cyclone.

Global warming has already been observed in the Sahel, and the consequences have not necessarily been bad: overall, precipitation has increased, and farmers have benefited, although in a dryland region south of the Sahara where people have endured a 2,000-year history of periodic drought, famine remains a constant hazard.

And now, so do massive downpours of rain: the Sahel storms. British and French scientists examined 35 years of satellite data and the rain gauges in the region to identify a rise in extreme daily rainfall totals. They found 85% of extreme rainfall cases coincided with satellite records of a passing mesoscale convection system.

They also examined the pattern of temperatures over the region and found that although the annual average temperatures have risen, the so-called “wet season” temperatures have remained steady. That is, locally warmer conditions alone have not brought more rainfall.

“Global warming is expected to produce more intense storms, but we were shocked to see the speed of changes taking place in this region of Africa”

Instead, they blame man-made global warming which has changed wind and rain conditions, and this will go on strengthening during this century, “suggesting the Sahel will experience particularly marked increases in extreme rain,” they conclude.

“Global warming is expected to produce more intense storms, but we were shocked to see the speed of changes taking place in this region of Africa,” said Christopher Taylor, a meteorologist at the UK’s Centre for Ecology and Hydrology, who led the study.

His co-author Douglas Parker, professor of meteorology at the University of Leeds in the UK, said: “African storms are highly organised meteorological engines, whose currents extract water from the air to produce torrential rain.

“We have seen these engines becoming more efficient over recent decades, with resulting increases in the frequency of hazardous events.” 

http://climatenewsnetwork.net/climate-change-brings-more-sahel-storms

Evidence stretching back 40,000 years shows that global warming will increase drying in a region of East Africa where drought already causes humanitarian crises

by Alex Kirby, Climate News Network, October 10, 2015

LONDON – One of Africa’s most volatile regions has become increasingly dry over the last century and faces a future of rising tension if this trend continues, US researchers say.

They say the rate of drying in the Horn of Africa is both unusual in the context of the last 2,000 years and in step with human-influenced warming. And they think the drying will continue as the region warms.

“Right now, aid groups are expecting a wetter, greener future for the Horn of Africa, but our findings show that the exact opposite is occurring,” says one of the study’s co-authors, Peter deMenocal, who heads the Center for Climate and Life at Columbia University’s Lamont-Doherty Earth Observatory.

“The region is drying, and will continue to do so with rising carbon emissions.” The study, published in the journal Science Advances, was based on evidence stretching back for 40,000 years.

Sediment core

The researchers used a sediment core they had extracted from the Gulf of Aden to infer past changes in temperature and aridity. After matching the core’s record with 20th-century observations, they concluded that drying is likely to continue across Somalia, Djibouti and Ethiopia.

That contradicts other models, which have suggested that future warming might bring rainier weather patterns that could benefit East Africa.

“What we see in the paleoclimate record from the last 2,000 years is evidence that the Horn of Africa is drier when there are warm conditions on Earth, and wetter when it is colder,” says lead author Jessica Tierney, associate professor of geosciences at the University of Arizona.

Global-scale models used to predict future changes as the climate warms suggest that the region should become wetter, primarily during the “short rains” season from September to November.

However, the new study suggests that those gains may be offset by declining rainfall during the “long rains” season from March to May, on which the region’s rain-fed agriculture relies.

The authors say the region has been racked with political instability and violence as it has dried. The Horn of Africa has suffered droughts every few years in recent decades − creating humanitarian crises as famine and violence spread.

In Somalia, as the political situation deteriorated amid the droughts of the 1980s and 1990s, hundreds of thousands of refugees fled the country, and pirates began raiding ships off the coast.

The 40,000-year-old sediment core has already yielded insights into Africa’s climate. In 2013, Tierney and deMenocal showed that the Sahara, which once used to burst into verdant life with regular rainfall, suddenly dried out over a century or two, during a warm period about 5,000 years ago – not more gradually, as many researchers had thought.

Their work provided evidence that climate shifts can happen quite suddenly, even if the forces driving them are gradual.

This latest study uses isotopes from leaf waxes found in the sediment sample to compare rates of drying over the past 2,000 years.

Plants reflect the environment that sustains them. When the climate is drier, leaf waxes are more enriched with deuterium, or heavy hydrogen isotopes, while leaf waxes from wetter climates reflect the more abundant rainfall through the presence of the normal hydrogen isotopes.

The researchers found an increasing shift toward heavy hydrogen in the last century as the climate − which had experienced a wet period during the Little Ice Age (1450-1850 AD) − dried out.

Climate modelling

Their findings suggest that climate modelling, frequently done at a global scale, would benefit from region-specific studies with higher-resolution results in high-impact areas such as the Horn of Africa

Tierney says: “If we can simulate rainfall in these arid tropical and subtropical regions better, we can understand the future impact of climate change.”

The development agency Oxfam says Ethiopia is facing a major emergency, with 4.5 million people needing food aid because of successive poor rains this year.

Oxfam’s representative in Ethiopia describes the situation − attributed to the El Niño periodic climate phenomenon in the Pacific − as “the start of a major emergency, which is expected to be serious and long.”

Meanwhile, parts of West Africa are suffering from the aftermath of severe floods − also attributed to El Niño − that have ruined crops and destroyed homes in Burkina Faso and Niger. 

Impact of climate change on staple food crop production in Nigeria, Climatic Change, September 2015; doi: 10.1007/s10584-015-1428-9

Climatic Change, 132(2) (September 2015) 321-336; doi: 10.1007/s10584-015-1428-9

Impact of climate change on staple food crop production in Nigeria

• Valentina Mereu
• , Gianluca Carboni
• , Andrea Gallo
• , Raffaello Cervigni
•  and Donatella Spano

Abstract

Climate change impact on the agricultural sector is expected to be significant and extensive in Sub-Saharan Africa, where projected increase in temperature and changes in precipitation patterns could determine sensible reductions in crop yields and concerns for food security achievement. This study presents a multi-model approach to analysing climate change impacts and associated risks for staple food crops in Nigeria. Previous attempts to evaluate climate change impacts in Nigeria had mainly focused on a reduced number of crops, with analysis limited to single experimental fields or specific areas, and in many cases considering only a limited number of climate models. In this work, crop simulation models implemented in the DSSAT-CSM software were used to evaluate climate change impacts on crop production in different Agro-Ecological Zones, considering multiple combinations of soils and climate conditions, varieties and crop management. The climate impact assessment was made using an ensemble of future climate projections, to include uncertainty related to climate projections. Even if precipitations could increase in most parts of Nigeria, this is not likely to offset the crop yield reduction due to the increase in temperatures, particularly over the medium-term period (2050), with yield decreases projected especially for cereals. The short-term effects are more uncertain and yields for cassava and millet might actually increase by 2020. Moreover, yield reductions are only partially mitigated by the direct effect of increased CO₂ atmospheric concentrations enhancing crop yields. In both periods and for all crops, there is a higher risk that crop yields may fall below the actual risk threshold.

http://link.springer.com/article/10.1007/s10584-015-1428-9

NASA Finds Drought May Take Toll on Congo Rainforest

A View of the entire African rainforest area (green) transitions into a view of the region included in the Nature study, primarily in the Congo forest (mostly brown). The study area represents intact areas in the Congo rainforest where satellite data are high quality. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio
› Larger image

from NASA's Jet Propulsion Laboratory, April 23, 2014

A new analysis of NASA satellite data shows Africa's Congo rainforest, the second-largest tropical rainforest in the world, has undergone a large-scale decline in greenness over the past decade.

The study, led by Liming Zhou of University at Albany, State University of New York, shows between 2000 and 2012 the decline affected an increasing amount of forest area and intensified. The research, published Wednesday in Nature, is one of the most comprehensive observational studies to explore the effects of long-term drought on the Congo rainforest using several independent satellite sensors.

"It's important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate," Zhou said.

Scientists use the satellite-derived "greenness" of forest regions as one indicator of a forest's health. While this study looks specifically at the impact of a persistent drought in the Congo region since 2000, researchers say that a continued drying trend might alter the composition and structure of the Congo rainforest, affecting its biodiversity and carbon storage.

Previous research used satellite-based measurements of vegetation greenness to investigate changes in the Amazon rainforest, notably the effects of severe short-term droughts in 2005 and 2010. Until now, little attention has been paid to African rainforests, where ground measurements are even sparser than in the Amazon and where droughts are less severe but last longer.

To clarify the impact of long-term drought on the Congo rainforest, Zhou and colleagues set out to see whether they could detect a trend in a satellite measure of vegetation greenness called the Enhanced Vegetation Index. This measure is developed from data produced by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite. The scientists focused their analysis on intact, forested regions in the Congo Basin during the months of April, May and June each year - the first of the area's two peak rainy and growing seasons each year.

The study found a gradually decreasing trend in Congo rainforest greenness. The decrease, sometimes referred to as "browning," suggests a slow adjustment to the long-term drying trend. This is in contrast to the more immediate response seen in the Amazon, such as large-scale tree mortality, brought about by more episodic drought events.

The browning of the forest canopy is consistent with observed decreases in the amount of water available to plants, whether that is in the form of rainfall, water stored in the ground, water in near-surface soils, or water within the vegetation.

These changes in available water were detected in part with NASA satellites including the NASA/JAXA Tropical Rainfall Measuring Mission, NASA's Quick Scatterometer (QuikScat), and NASA's Gravity Recovery and Climate Experiment, a joint mission with the German Aerospace Center. The latter two missions are managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

"Combining measurements from different sensors has given us more confidence in the results of the MODIS data and provided us with insights into the environmental and physiological mechanisms of the browning observed by the MODIS data," said co-author Sassan Saatchi of JPL.

Climate factors known to affect vegetation growth were also in line with the observed browning. Land surface temperatures, for example, were observed to increase over most of the study area. Decreased cloudiness allowed more solar radiation to reach the plants, which typically promotes photosynthesis, but in this case it likely posed an extra stress on the plants from the resulting depletion of soil moisture.

"Forests of the Congo Basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years," Saatchi said. "However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests."

How the changes affect individual plant species in the area remains to be seen. For example, drier conditions may favor deciduous trees at the expense of evergreen trees.

"Our assessment is a step toward an improved understanding of how African rainforests respond to increasing drought," Zhou said. "We need to consider the complex range of processes affecting different tropical rainforest species before we can fully assess the future resilience of tropical forests."

The other authors for this research include Yuhong Tian at I.M. Systems Group, Inc. at the Center for Satellite Applications and Research, the science arm of National Oceanic and Atmospheric Administration's Satellite and Information Service, College Park, Md.; Ranga Myneni at Boston University in Massachusetts; Philippe Ciais at Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette Cedex, France; Yi Y. Liu at University of New South Wales, Australia; Shilong Piao at Peking University, China; Haishan Chen at Nanjing University of Information Science and Technology, China; Eric Vermote of NASA's Goddard Space Flight Center, Greenbelt, Md.; and Conghe Song and Taehee Hwang at the University of North Carolina at Chapel Hill.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

http://www.jpl.nasa.gov/news/news.php?release=2014-124

Congo forest feels bigger climate impact

by Tim Radford, Climate News Network, April 25, 2014

Researchers say there is increasing evidence that climate change is among the factors causing serious damage to the rainforest of the Congo basin.

LONDON, 25 April - The Congo – one of the world’s greatest rainforests – is getting steadily less green. The slow change in colour during this century, recorded by a series of US satellites, has been matched by a rise in temperature and lower precipitation. And, researchers think, it could reflect a forest’s response to climate change.

Scientists from Australia, China, the US and France report in the journal Nature that they examined optical, thermal, microwave and gravity data collected by orbiting sensors between 2000 and 2012.

They concentrated on intact forested regions during the months of April, May and June each year, which span the peaks of growth and rainfall. They detected an intensification in the forest’s decline. This decline was consistent with lower rainfall, poorer water storage below the canopy and a gradual change in the composition of species.

“It is important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate,” said Liming Zhou, of Albany State University of New York. But other factors could accelerate this “browning” of one of the world’s greatest rainforests.

Half as hot again

A team from the Catholic University of Louvain in Belgium - also known in Belgium’s other language as KU Leuven - predicts in the Journal of Climate that explosive population growth and inefficient agricultural practices are likely to make things a great deal hotter for the region and a great deal worse for the rainforest.

By 2050, according to their computer models, Central Africa will be on average 1.4 °C hotter than it is today just because of greenhouse gas emissions. And the steady destruction of the forest will add an extra 0.7 °C to that figure.

Temperature increases on such a scale will harm plant and animal species and even bring about some extinction. Where the forests have been cleared, there will be increased levels of evaporation, and consequent rises in temperature.

Across the Atlantic, things also look bleak for the Amazon rainforest. Paulo Brando of the Amazon Environmental Research Institute in Brazil and colleagues from the US report in the Proceedings of the National Academy of Sciences that the piecemeal clearing of the rainforest, along with drought, has begun to create “tinderbox” conditions  and an ever more destructive cycle of burning.

Non-average menace

Over the course of 8 years, in one of the longest-running experiments of its kind, the researchers burned 50-hectare plots of forest in the south-eastern Amazon, a region vulnerable to climate change. They compared the tree deaths each year to measure the impact of drought on fire intensity.

“Drought causes more intense and widespread fires,” said Dr Brando. “Four times more adult trees were killed by fire during a drought year, which means that there was also more carbon dioxide released into the atmosphere, more tree species loss and a greater likelihood of grasses invading the forest.”

This research, too, was backed up by satellite observation. In 2007, a year of drought, fires in south-east Amazonia burned 10 times more forest than in an average year - an area equivalent to a million soccer fields, according to Douglas Morton of the US space agency NASA, a co-author.

Climate change is expected to bring shorter, more intense rainy seasons and longer dry seasons in the region. Michael Coe of Woods Hole Research Center, another author, said “We tend to think only about average conditions, but it is the non-average conditions we have to worry about.”