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Date of publication: October 2020
Extracts from the document, pages: 7, 9-13, 18, 20-21, 23
State of the climate indicators
TEMPERATURE AND PRECIPITATION
Temperature and precipitation are two key indicators that characterize the state of the climate in Africa and which have continuously affected living conditions in African societies. Agriculture, food security and water resources are strongly impacted by variations in these two indicators. Agriculture contributes to a significant portion of the gross domestic product (GDP) of many African nations and provides a major source of employment.
Crop performance in particular, which is based predominately on rainfed agriculture, is highly sensitive to temperature and precipitation variations. Increases in temperature and changes in rainfall patterns also significantly affect population health across Africa. Warmer temperatures and higher rainfall increase habitat suitability for biting insects and the transmission of vector-borne diseases such as dengue fever, malaria and yellow fever. The monitoring and prediction of these two indicators therefore constitute a primary entry point to analyse the state of the African climate and associated impacts.
TEMPERATURE OVER THE AFRICAN CONTINENT
African temperatures in recent decades have been warming at a rate comparable to that of most other continents, and thus somewhat faster than global mean surface temperature, which incorporates a large ocean component. Averaged across mainland Africa, at 0.56 °C to 0.63 °C above the 1981–2010 long-term mean, 2019 was most likely the third warmest year on record, following 2010 and 2016. Both 2010 and 2016 were also warm years globally due in part to El Niño conditions at the start of the year.
There were regional variations in temperature anomalies at a subcontinental scale in 2019. Temperatures exceeding 2 °C above the 1981–2010 average were recorded in South Africa, Namibia and parts of Angola. Large areas extending from the south to the north of the continent were more than 1 °C above normal. Only limited areas in the north-west, including Mauritania, as well as adjacent ocean areas, were slightly cooler than the 1981–2010 average.
Annual precipitation totals in 2019 were below the long-term means in Southern Africa, east of the Gulf of Guinea, along the south-west coast of West Africa, north-west of the High Atlas Mountains, on the Madeira and Canary Islands, and in some regions of Madagascar. Above-normal precipitation fell in northern and southern Madagascar, in East Africa, in much of the Sahel, between the Volta and Niger Rivers, north of the lower Congo River and in western Central Africa.
Annual precipitation totals very much above average (above the 90th percentile) were observed in Central and East Africa. Very low annual precipitation totals (below the 10th percentile) were found in most of Southern Africa, east of the Gulf of Guinea, north-west of the High Atlas Mountains and on the Canary Islands.
SEA-SURFACE TEMPERATURES INFLUENCED PRECIPITATION AND OTHER CLIMATE FEATURES
Sea-surface temperatures (SSTs) were above average across large areas of the globe in 2019. Tropical Pacific SSTs briefly reached the threshold of El Niño conditions early in the year but reverted to neutral conditions thereafter. The lack of a typical El Niño-like pattern in global precipitation was consistent with the relatively weak SST El Niño signal. Above-normal precipitation in the Greater Horn of Africa and below-normal precipitation in Southern Africa in 2019 are both consistent with El Niño conditions, however.
The latest forecast, covering the five-year period from 2020 to 2024, shows continued warming especially over North and Southern Africa
Indian Ocean SSTs played an important role in the events of 2019 around the Indian Ocean basin. In the latter half of the year, warmer than average waters in the western Indian Ocean and cooler than average temperatures in the east of the basin along the west coast of Indonesia – a pattern characteristic of a very strong positive phase of the IOD were also associated with well above-average precipitation in parts of East Africa from October to December.
The south-western Indian Ocean also saw much higher than average tropical cyclone activity during the 2018/2019 season. Over this region, there were positive SST anomalies, along with a neutral but positive phase of the El Niño–Southern Oscillation and positive IOD. These influences are associated with more precipitation and cyclone activity over the western side of the Indian Ocean basin.
NEAR-TERM PREDICTIONS FOR 2020–2024
Annual to decadal climate predictions (ADCP) provide decision makers with information on near-term climate by starting forecasts from the observed state of the climate system. Such forecasts are updated annually by several international centres and collected by the WMO Lead Centre for ADCP. Due to their experimental status, it is important to monitor the annual updates of these predictions. The latest forecast, covering the five-year period from 2020 to 2024, shows continued warming especially over North and Southern Africa, with a dominant decreasing rainfall feature in both subregions and increased rainfall over the Sahel.
These predictions are consistent with the amplified warming over land and at high northern latitudes expected from increased atmospheric concentrations of greenhouse gases and the northward shift of the Atlantic Intertropical Convergence Zone expected from warmer temperatures in the North Atlantic Ocean than in the South Atlantic Ocean.
OCEAN HEAT CONTENT AND SEA LEVELS
OCEAN HEAT CONTENT
On timescales longer than about a year, the vast majority (more than 90%) of the Earth’s energy imbalance goes into heating the oceans. Ocean heat content (OHC) is a measure of the amount of heat in the ocean as a whole and is a more comprehensive measure of the amount of heat in the marine part of the climate system than SST. As the oceans warm, they expand, resulting in both global and regional sea-level rise. Increased OHC accounts for about 40% of the observed global sea-level increase over the past 60 years.
The capacity to measure OHC in the upper layers of the ocean, particularly the uppermost 700 metres, has improved dramatically in the twenty-first century as a result of the deployment of the network of Argo profiling floats, which make regular profiles of the upper ocean across most of the world’s oceans. Tracking ocean temperatures and associated changes in OHC allows us to monitor variations in the Earth’s energy imbalance over time.
The global mean sea level has risen since the early 1990s, with an average rate of 3.2 +/- 0.3 mm/year and an acceleration of ~0.1 mm/year. However, the rate of rise is far from regionally uniform. In some areas of the oceans, the rate is between two and three times higher than the global mean as measured by satellite altimetry. There is significant regional variability in sea-level trends around Africa. In the West African region, especially between 10°N and 10°S, the rate of sea-level rise is slightly above the global mean (3.5–4.0 mm/year).
The global mean sea level has risen since the early 1990s
Some East African regions display higher trends (4.0–5.0 mm/year). These include north-eastern Africa (Egypt and the Nile Delta region) and countries along the Red Sea and Oman Gulf, as well as Mozambique and the Indian Ocean side of South Africa. Trends exceeding 5 mm/year have been observed in the south-western Indian Ocean from Madagascar eastward towards and beyond Mauritius. These regional trends are mostly driven by non-uniform ocean thermal expansion, reflecting non-uniform heat storage in the upper ocean layers. In all other parts of the African region, sea-level trends are on the same order of magnitude as the global mean.
Conventional satellite altimetry measures open ocean sea-level change up to ~10 km from the coast. However, dedicated processing methodologies applied to satellite altimetry allow the rate of sea-level change to be estimated very close to the coast (within 1 to 4 km). Recent results suggest that at some sites along African coastlines, the rate of sea-level rise can differ from the rate offshore. There are differences in sea-level trends between 15 km offshore and within the first few kilometres of the coast for the period 2002–2018.
This may result from a variety of small-scale coastal processes, for example, coastal currents, trends in waves, freshwater runoff in river estuaries, and so forth. Such coastal processes may either amplify or attenuate the regional trends observed offshore. While the general impacts of climate-related sea-level rise are well known, the number of studies of the African continent is limited due to the lack of systematic in situ observations and modelling exercises.
About 56% of the coastlines in Benin, Côte d’Ivoire, Senegal and Togo are eroding, at an average rate of 1.8 m/year
It has been reported that parts of the West African coasts currently experience accelerated degradation related to pluvial and fluvial floods, high winds and waves, storm surges, damages to critical ecosystems (mangroves, marine habitats) and human development along the coast. Coastal erosion, especially of low-lying sandy and muddy coasts, is widespread in this region and partly attributed to alongshore sediment transport resulting from changes in wave regime and human intervention such as the building of river dams and coastal urbanization.
About 56% of the coastlines in Benin, Côte d’Ivoire, Senegal and Togo are eroding, at an average rate of 1.8 m/year. In all countries, the cost of erosion is expected to increase considerably in the future. While today, sea-level rise is not a dominant contributor to coastal erosion in West Africa, the expected acceleration in the rate of sea-level rise in the coming decades will combine with other factors to exacerbate the negative consequences of environmental changes.
Risks and impacts on food security and population
In addition to conflicts, instability and economic crises, climate variability and extreme weather and climate events are among the key drivers of the recent increase in global hunger. After decades of decline, food insecurity and undernourishment are on the rise in almost all subregions of sub-Saharan Africa. In drought-prone sub-Saharan African countries, the number of undernourished people has increased by 45.6% since 2012 according to FAO.
The year 2019 recorded a deteriorating food security situation in sub-Saharan Africa, as well as increased population displacement and the increased food insecurity of those displaced people. Refugee populations often reside in climate “hot spots”, where they are exposed to and affected by slow and sudden-onset hazards, resulting in some cases in secondary displacements.
CENTRAL AND WEST AFRICA
Of the 5 135 000 forcibly displaced persons identified by IOM across six countries in Central and West Africa, 4%, or approximately 180 700 individuals, were displaced by natural disasters. In its 2020 Global Report on Internal Displacement (GRID), the Internal Displacement Monitoring Centre (IDMC) reported 649 448 new disaster-induced displacements in West and Central Africa, mainly due to ﬂoods. While conﬂict remained the major driver of food insecurity in Central Africa, damages associated with floods and pests further exacerbated the situation in aﬀected areas.
These factors disrupted agricultural activities and triggered an increase in staple food prices, aﬀecting livelihoods and constraining access to food across the region. Despite localized production shortfalls due to ﬂoods, pests and conﬂict, the aggregate regional production of cereals in 2019 was close to the previous five-year average of about five million tons.
West Africa was also hit by ﬂoods due to heavy precipitation in July and August. This resulted in localized crop and livestock losses and population displacement in several countries. According to IOM, 66 800 people were displaced in Nigeria as a result of disasters as of January 2020, representing 3% of the 2 600 000 individuals displaced in the country.
IMPLICATIONS FOR AGRICULTURE AND FOOD SECURITY
Africa faces significant challenges in addressing climate change risks, including increasing temperature, changing precipitation patterns, rising sea levels and more frequent extreme weather and climate events. These risks are becoming more severe as the environment is rapidly warming and have a pronounced eﬀect on the agricultural sector. Agriculture is the backbone of Africa’s economy and accounts for the majority of livelihoods across the continent.
Africa is therefore a vulnerability “hot spot” for the impacts of climate variability and change
Africa is therefore a vulnerability “hot spot” for the impacts of climate variability and change. Key risks to agriculture include reduced crop productivity associated with heat and drought stress and increased pest damage, disease damage and ﬂood impacts on food system infrastructure, resulting in serious adverse eﬀects on food security and on livelihoods at the regional, national and individual household levels.
These risks and their consequent eﬀects have been identified with “high confidence”, and the level of risk has been identified as “very high” if the global mean temperature increases 2 °C and 4 °C above pre-industrial levels by 2080–2100. By the middle of this century, major cereal crops grown across Africa will be adversely impacted, albeit with regional variability and diﬀerences between crops.
Under the RCP 8.5 climate change scenario, a reduction in mean yield of 13% is projected in West and Central Africa, 11% in North Africa, and 8% in East and Southern Africa. Millet and sorghum have been found to be the most promising crops, with a yield loss by 2050 of just 5% and 8%, respectively, due to their greater resilience to heat-stress conditions, while rice and wheat are expected to be the most aﬀected crops with a yield loss by 2050 of 12% and 21%, respectively.
Climate change has widespread eﬀects on human health, impacting both environmental and social determinants. Africa is particularly at risk for the health eﬀects of climate change because it has high burdens of climate-sensitive diseases and low preparedness and adaptive and response capacity at the institutional and community levels. Increases in temperature as well as changes in rainfall patterns also contribute to infectious disease transmission across Africa.
Warmer temperatures and higher rainfall increase suitability for habitats of biting insects and transmission of vector-borne diseases such as dengue fever, malaria and yellow fever. In addition, new diseases are emerging in African regions where they were previously not present. In 2017, an estimated 93% of global malaria deaths occurred in Africa; children are the most vulnerable to this disease, and pregnant women are another high-risk group.
Malaria epidemics often occur after periods of unusually heavy rainfall, such as those associated with El Niño events in parts of East Africa. In addition, warming in the East African highlands is allowing malaria-carrying mosquitoes to survive at higher altitudes, endangering new populations that were previously less aﬀected by and are less resistant to the disease.
Source photo : WMO