Les défis liés au réchauffement climatique dans les Régions Intertropicales

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1 Les défis liés au réchauffement climatique dans les Régions Intertropicales Thierry LEBEL IRD Laboratoire d étude des Transferts en Hydrologie et Environnement Observatoire des Sciences de l Univers de Grenoble - OSUG 1

2 Temperature and Water The two key components of our climate 2

3 + 0,8 globally but strong differences Temperature differences between and

4 Climate warming in Africa since the 1970 s Over the last 100 years: Unequivocal temperature rise Last century in Africa Temperature Anomaly ( c) Anomalie de température ( C) Anomalie de tempéra Temperature rise 1.2 C since the early 20 th Century Higher than the global increase, and accelerating since 1990 Sea level rise of 18 cm during the 20th century Temperature Anomaly ( c) Anomalie de température ( C) Global Anomalie de température ( C) I

5 Scenarios Heat Waves becoming a major concern Likely: 600 ppm COP21 Target: 500 ppm Present: 400 ppm in the atmosphere At a 500 ppm CO2 concentration (RCP 2.6), exceptional Heat Waves (+3 σ) will become current in the intertropical band, that is 50 % of summers in West, Central and East Africa In the RCP 8.5 scenario (+4,5 c), the 3 σ episods will concern 85 % of continental surfaces in 2100, and 5 σ episods (never experienced), 60 %. Major impact on crop yields, but also primary impacts on health (see 2003 heat wave in Europe); becoming a very serious public health issue in West Africa I

6 From temperature increase to water cycle disruption Unprecedented CO2 concentration, rising emissions, soaring temperature Climate models pretty robust at predicting global increase of temperature, as well as regional trends More difficult for Rainfall, because much larger natural variability and regional specificities 6

7 1. Africa: a Fresh Water Scarcity Continent The West African drought The largest regional climate signal since the pre-industrial age Humid Dry Recovery?

8 1. Africa: a Fresh Water Scarcity Continent The Clausius-Clapeyron Law predicts : 6.5% increase of water vapour saturation / K (in a perfect world)

9 Other major changes as well Histogram of the Population increasing rate population Number of countries Bénin Niger -1% % 1% 2% 3.5 3% 4% 5% World Africa West Africa surface cultivée (milliers d'hectares) Cultivated area (1000 ha) surface cultivée population du Niger Niger Population The necessity to go beyond the stage of Climatic Alert; looking at the global Earth System and Global Changes that affect it. Short time versus long time issues, but a continuity of problems related to global change, mostly due to Intensification : Climate (Precip., Temperature), Water resources (Runoff, Water demand), Food demand (demographic pressure, feeding people), Health Issues (environmental factors favoring the spreading of vectorial& infectious diseases, emerging diseases) I

10 Water at the heart of the Earth Climate The Water cycle is at the heart of the Earth climate : key driver in redistributing the energy at the Earth Surface Rainfall and Temperature are the two main climatic drivers of the Water Cycle; both are changing fast; not similar everywhere Warmer Temperatures + more intense but fewer rainfall events ---> A more extreme climate More intense rainfall and higher temperatures ---> Strong influence on food security and health issues through a complex chain of factors that we need to better understand 10