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Drought in the Sahel : global and local driving forces and their impact on vegetation in the 20th and 21st century

Klönne, Uta LU (2012) In Student thesis series INES NGEK01 20121
Dept of Physical Geography and Ecosystem Science
Abstract (Swedish)
Populärvetenskaplig sammanfattning
Klimatet i region Sahel varierar på en årlig och decennielång basis. Under slutet av 1900-talet
har den utsätts för en period av markant torka. Mellan 1960 och 1990 nådde nederbörden nivåer
av bara 40 % av genomsnittet. På grund av detta skattas perioden en av de makantaste klimatiska
fenomen i hela världen under 1900-talet. Torkan har orsakat stora konsekvenser för invånarna
och ekosystem i området, till exempel i form av begränsad tillgänglighet i vatten som därmed har
lett till förlust i gröda, boskap och hungersnöd. En stor mängd studier har utförts på drivkrafterna
som orsakad torkan. I början skyllde man på befolkningen som anklagades för att använt marken
på fel sätt. En förbättring i... (More)
Populärvetenskaplig sammanfattning
Klimatet i region Sahel varierar på en årlig och decennielång basis. Under slutet av 1900-talet
har den utsätts för en period av markant torka. Mellan 1960 och 1990 nådde nederbörden nivåer
av bara 40 % av genomsnittet. På grund av detta skattas perioden en av de makantaste klimatiska
fenomen i hela världen under 1900-talet. Torkan har orsakat stora konsekvenser för invånarna
och ekosystem i området, till exempel i form av begränsad tillgänglighet i vatten som därmed har
lett till förlust i gröda, boskap och hungersnöd. En stor mängd studier har utförts på drivkrafterna
som orsakad torkan. I början skyllde man på befolkningen som anklagades för att använt marken
på fel sätt. En förbättring i modellering har avslöjat att torkan i stort sett är orsakad av
förändringar i ytvattentemperaturen. Uppvärmningen av Indiska oceanen och Stilla havet samt
skillnaden i temperaturer mellan norra och södra delar av Atlantiska oceanen är orsaken till
torkan. Förändringar i den Indiska oceanen har tydligt den största påverkan. Modellerna som
representerar torkan är mer framgångsrika i fall lokala återkopplingsmekanismer ingår i
evalueringen. De viktigaste återkopplingsmekanismer, vegetation och partiklar från jordytan, kan
förstarka och dämpa den initiala förändringen. Utom de naturliga drivkrafterna finns det
antropogena processer som har en påverkan på torkan, i praktiken har den växande användningen
av västhusgaser en ökande betydelse. Det finns ingen enighet i växthusgasernas relativa
påverkan, men de kommer att ha en större roll i framtiden. På grund av den stora variationen i
nederbörd har vegetationen i Sahel förändrats mycket under 1900-talet. Efter en period av stark
nedgång har vegetationen återhämtat sig på grund av en växande nederbörd på 90-talet.
Människans påverkan i form av växande population och landsbruk, har visat sig ha haft en liten
effekt, men som troligen kommer växa i framtiden. Det är oklart hur nederbörden och
vegetationens mängd kommer att förändra situationen i framtiden. Vissa modeller simulerar
torkan medan vissa förutser mer regn. Större regnnivå tillsammans med en växande användning
av växthusgas kan även leda till en grönare Sahel. Under det nuvarande klimatförhållandet,
förblir både torkan och det gröna Sahel stabila. Regionen identifieras såvida som en möjlig
”tipping element”. (Less)
Abstract
The Sahel is a region of large interannual and interdecadal climatic variability. In the late 20th century it experienced a period of pronounced drought that lasted from the late 1960 to the early 1990s, where precipitation values reached only about 40% of the long-term mean. This is why this period counts among one of the most striking climatic phenomena worldwide in the 20th century. The consequences on societies and ecosystems of the region include reduced water availability leading to crop failures, livestock decline and food shortages. Extensive research has been carried out on the driving forces behind this period. In the beginning it was attributed to mismanagement of the land by the local people, leading to land degradation and... (More)
The Sahel is a region of large interannual and interdecadal climatic variability. In the late 20th century it experienced a period of pronounced drought that lasted from the late 1960 to the early 1990s, where precipitation values reached only about 40% of the long-term mean. This is why this period counts among one of the most striking climatic phenomena worldwide in the 20th century. The consequences on societies and ecosystems of the region include reduced water availability leading to crop failures, livestock decline and food shortages. Extensive research has been carried out on the driving forces behind this period. In the beginning it was attributed to mismanagement of the land by the local people, leading to land degradation and desertification. However, with an improvement in modelling it has been revealed that the droughts can mainly be attributed to changes in the sea surface temperatures (SSTs). A warming of the Indian and the Pacific as well as a differential heating of the Atlantic Ocean have been found to lead to drought conditions. Despite varying modelling results, the Indian Ocean is likely to play the dominant role. However, models reproduce past droughts more successfully if they additionally include local feedback mechanisms. The most important ones are vegetation and atmospheric dust, which can both amplify or dampen the initial change. Apart from the natural driving forces there is a growing anthropogenic effect on droughts in the form of the rising concentration of greenhouse gases (GHGs). Their contribution is still disputed, but is likely to grow in the future. Due to the large variability in precipitation, the vegetation underwent considerable changes in the 20th century. After substantial declines it recovered again in the 1990s along with rising precipitation values. The effect of humans through demographic and agricultural pressures has been found to be small, but it may well grow in the future. Future projections of rainfall as well as vegetation cover in the Sahel region are highly uncertain. Some models simulate drying, whereas others predict a further improvement in rains. Together with an increased GHG forcing this may even cause a greening up of the Sahel. Under present climatic conditions, both the dry and the green state have been found to be stable, identifying the region as a possible “tipping element”. (Less)
Please use this url to cite or link to this publication:
author
Klönne, Uta LU
supervisor
organization
alternative title
Torkan i Sahel : globala och lokala drivkrafter
course
NGEK01 20121
year
type
M2 - Bachelor Degree
subject
keywords
Sahel, Geography, Physical Geography, Torka, Naturgeografi, Geografi, Vegetation, Drought
publication/series
Student thesis series INES
report number
239
language
English
additional info
External supervisor Prof. Dr. Wilfried Endlicher,
Department of Geography, Humboldt-University of Berlin
id
2796921
date added to LUP
2012-08-21 12:30:07
date last changed
2012-08-21 12:30:07
@misc{2796921,
  abstract     = {The Sahel is a region of large interannual and interdecadal climatic variability. In the late 20th century it experienced a period of pronounced drought that lasted from the late 1960 to the early 1990s, where precipitation values reached only about 40% of the long-term mean. This is why this period counts among one of the most striking climatic phenomena worldwide in the 20th century. The consequences on societies and ecosystems of the region include reduced water availability leading to crop failures, livestock decline and food shortages. Extensive research has been carried out on the driving forces behind this period. In the beginning it was attributed to mismanagement of the land by the local people, leading to land degradation and desertification. However, with an improvement in modelling it has been revealed that the droughts can mainly be attributed to changes in the sea surface temperatures (SSTs). A warming of the Indian and the Pacific as well as a differential heating of the Atlantic Ocean have been found to lead to drought conditions. Despite varying modelling results, the Indian Ocean is likely to play the dominant role. However, models reproduce past droughts more successfully if they additionally include local feedback mechanisms. The most important ones are vegetation and atmospheric dust, which can both amplify or dampen the initial change. Apart from the natural driving forces there is a growing anthropogenic effect on droughts in the form of the rising concentration of greenhouse gases (GHGs). Their contribution is still disputed, but is likely to grow in the future. Due to the large variability in precipitation, the vegetation underwent considerable changes in the 20th century. After substantial declines it recovered again in the 1990s along with rising precipitation values. The effect of humans through demographic and agricultural pressures has been found to be small, but it may well grow in the future. Future projections of rainfall as well as vegetation cover in the Sahel region are highly uncertain. Some models simulate drying, whereas others predict a further improvement in rains. Together with an increased GHG forcing this may even cause a greening up of the Sahel. Under present climatic conditions, both the dry and the green state have been found to be stable, identifying the region as a possible “tipping element”.},
  author       = {Klönne, Uta},
  keyword      = {Sahel,Geography,Physical Geography,Torka,Naturgeografi,Geografi,Vegetation,Drought},
  language     = {eng},
  note         = {Student Paper},
  series       = {Student thesis series INES},
  title        = {Drought in the Sahel : global and local driving forces and their impact on vegetation in the 20th and 21st century},
  year         = {2012},
}