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Effects on the Wet/Dry Savannah (Tropical Continental Climate in W. Africa)
Climate change could have far reaching effects on the global climate as temperatures continue to rise
and as the amount of water circulating in the atmosphere increases in its proportion. These effects
could be especially felt in the sensitive Savannah regions which experience a tropical continental
climate, one such place being Kano, Nigeria (12oN).
Savannah grasslands represent unique sensitive ecosystems which are characterised by mainly
tall elephant grass which is broken by scattered isolated trees and shrubs. Many scientists fear that
this ecosystem could be taken over by woody trees and shrubs which are likely to colonise
through vegetation succession as the Sahel experiences greater precipitation over the next 50 years.
The savannahs in their current state are both ecologically unique and economically vital for the survival
of communities who live in these areas. Colorado State University published research in the
scientific Journal Nature (2005) that rainfall is the most important controlling factor on savannah
development. From this work came two classifications:
Stable savannahs - are those that receive less than 650mm of rainfall per year and subsequently allows
tree growth to be restricted and therefore grasses can co-exist.
Unstable Savannahs – receive more than 650mm rainfall per year. The amount of trees in such
savannahs is not controlled by the amount of rainfall alone at present, but by the regulating effect
of fires and grazing by wild animals which clear grasses and encourage tree growth. Trees in these
regions such as the Baobab Tree have become adapted to fires (pyrophytic adaptations such as thick
fire resistant bark) and survive preferentially over grasses.
Kano currently has an average rainfall of 1040mm so therefore the savannah is already classed
as unstable and increased rainfall can only act to further encourage tress and result in the demise of
the grassland habitat! Complete loss of this sensitive ecosystem is likely in this region in the next 50
years as the average precipitation is set to increase in the majority of climate change models.
The balance between trees and grasslands influences vital characteristics of the ecosystem such as
livestock production as well as water balance and as a result drinking water supplies. Changes to
the grasslands that cause a reduction in the species diversity would be fundamentally detrimental to
local indigenous tribes who have adopted a sustainable way of life over hundreds of years. As well as
threatening the viability of indigenous populations, climate change may well damage local tourism
in countries such as Nigeria that rely on it heavily for revenue which funds investment and development.
Climate change may well threaten and decrease the species diversity and ecology of game reserves
that so many tourists come especially to witness. Although more trees would mean more elephants
generally, an invasion of trees would cut down on the number of other large mammals in the savannah
which is bad news for safari based tourism.
Diagram below is to show increased rainfall would produce a savannah more characteristic of
the equatorial latitudes i.e. parkland „closed savannah‟:
You need to know what drives the savannahs in order to help manage them as climate conditions change.
Two schools of thought exist when trying to explain their origin, firstly rainfall is important in their
development and secondly disturbances such as fire and grazing help regulate them. It is most likely that
both of these factors are responsible for regulating the savannah depending on the point at which they
occur in the season (i.e. wet/dry). There is dispute about the future of much of North Africa under climate
change, underscoring the difficulties in assessing one of the most complex mechanisms on the planet.
However, climate change might have some beneficial effects too for the tropical continental regions of
West Africa. Rising temperatures in the Sahara desert could actually be beneficial, reducing drought in
the Sahel region immediately south of it. The Royal Netherlands Meteorological Institute were the first
to consider the roles of both land and sea-surface temperatures.
The Haarsma computer model suggests that if emissions of greenhouse gases are not reduced, higher
temperatures over the Sahara would cause 25% to 50% extra daily rainfall in the Sahel by 2080
during the months from July to September. The Sahara desert heats up faster than the oceans,
creating lower atmospheric pressure above the sands. This in turn leads to more moisture moving in from
the Atlantic to the Sahel. Also warmer air has a higher capacity to hold moisture allowing greater precipitation
to the south of the Sahara Desert.
Additional rainfall would allow greater agricultural yields, growth of a greater range of crops and
create a longer growing season as it is likely that the wet season may lengthen. Evidence from the
Journal Biosciences (2002) confirms notions of a wetter climate and suggests that further north in the dry
desert climatic zone, parts of the Sahara Desert are showing signs of ‗greening‘ due to increased rainfall
(1982-2002). This has made some in the scientific community predict a return to the Sahara Desert being
a lush green savannah again as it was some 12,000 years ago!
However on the downside climate change could disrupt the pattern of seasonal rains that is brought
about by the movement of the ITCZ north over Kano. It is the associated movement of the ICTZ seasonally
in the summer months that brings Kano the SW Monsoon and therefore its wet season. If the ITCZ gets
‗stuck‘ too far south or fails to move as far north as 12 oN early enough in the wet season then the rains of
the Monsoon may not come and areas such as Kano may experience crop failures. Even if there is
more rain per year on average for this region, it is likely that rains may become more unreliable and the
above effects more likely.
Increased rainfall and increased likelihood of frequent extreme weather events such as prolonged
monsoon rainstorms would increase the likelihood of flooding in the region. Flash floods apart from
obvious short term effects such as damage to homes, business and people could also result in long term
effects such as soil erosion and actually lead to subsequent reduction in agricultural yields in places
least equipped to deal with such losses.
A wetter climate in this part of West Africa may also mean an increase in mosquitoes and therefore an
increase in malaria cases. Malaria is already endemic in Nigeria according to the WHO where the
mortality rate in children under five 729 per million. Other water borne diseases may become more
common as temperatures rise and the climate becomes wetter
The other side of the argument goes however, that global warming may have the opposite effect on this
region and cause drier conditions for West Africa as well as much of the continent as a whole and
desertification may result. Some predictions estimate a 50% drop in yields from rain fed agriculture by
2020.
Whichever prediction, (if any) comes to be the correct outcome for Tropical Continental West Africa in the
future, it is important to note that there will be regional disparities in terms of magnitude of the effects
suffered. For instance more marginal areas to the north of the region may suffer greater hardship from
increasingly unreliable rainfall patterns and shortened growing season and a more unpredictable climate.
Although not technically in the tropical continental region, places like Sudan would undoubtedly suffer
significantly from the effects of lower rainfall and famines such as those experienced in the 1980‘s. Famines
in the Sahel region would lead to mass migration of people to neighbouring countries and humanitarian
disasters would therefore be common place.