International programmes in the Gulf of Guinea (oceanography & climate)

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1 International programmes in the Gulf of Guinea (oceanography & climate) Bernard Bourlès, IRD/LEGOS (France) & CRHOB-CBRST (Benin) Co-Chair of PIRATA ISSG Member of AMMA ISSC Member of the TACE/CLIVAR Int. Obs. Group. Coordinator of EGEE/AMMA Co-coordinator of PROPAO

2 - General scientific context: Oceanic conditions in the eastern tropical Atlantic (and the Gulf of Guinea) and regional climate - International programs: PIRATA AMMA/EGEE TACE/CLIVAR

3 CLIMATIC CONTEXT: Oceanic conditions in the eastern tropical Atlantic (and the Gulf of Guinea) and regional climate Northward penetration of moist air from the Gulf of Guinea up to the Sahelian domain with strong influence on the WAM (development and intensity). February 2000 August 2000 High sea surface temperature variability (and thus fluxes variability) in this particular area! (cold tongue, equatorial and coastal upwellings)

4 The Gulf of Guinea is very badly simulated in numerical models SST Surface fluxes -Pb with fluxes; (eg wind stress, local air-sea interaction, convective heating over land of S. America and W. Africa) -Pb with mixing processes; - Pb with horizontal advection + interactions with subsurface Pb mostly in the GG -Pb with impacts of oceanic waves;

5 Coastal upwellings along African coasts & fisheries January July Mean Reynolds SST ( C), TAOSTA D20 contours (m), ER S wind stress (N/m²) Upwellings = main resource zones for fishing activities

6 COASTAL UPWELLING IN THE NORTHERN GULF OF GUINEA -Two upwelling seasons: -Main upwelling season from June to September; -Minor upwelling season from January to March. Mean SST ( ) in August. Hashed areas for SST<25 C ( From Bakun, 1978). 8 W 4 W 0 4 E Cot e d'ivoire Ghana -A remarkable characteristic: -No evident correlations between wind forcing and coastal temperature during the major upwelling season Potential regional climate impact? (impact on meridional surface temperature gradient) Ekman Transport SOUTH-WEST WIND 8 W 4 W 0 4 E Cot e d'ivoire Ghana Thermocline GUINEA CURRENT => Alternative mechanisms have been suggested: - Local wind stress and regional wind curl (but not for both seasons!). -Guinea Current may influence upwelling -Cape effect (no; may contribute to maxima) - Strong evidence of remote forcing by trapped Kelvin waves 8 W 4 W 0 4 E Cot e d'ivoire GUINEA CURRENT Ghana Analysis and data needed, But we ll have some new results during this colloquium!

7 Coastal upwelling variability and fisheries Sardinella aurita catches Sardinella aurita Evolution of Sardinella catch and sea surface temperature anomalies off Côte d Ivoire from 1970 to 1990 ; Augmentation of catches simultaneous to the augmentation of the coastal winter upwelling amplitude off Côte d Ivoire (source: Claude Roy, IRD). Characteristic seasonal cycles of monthly averaged mixed layer and photic depths, surface chlorophyll and rate of primary production, integrated and at the DCM. From Longhurst (1998). (trend suggesting an increase of the minor winter upwelling amplitude). To be confirmed! Note about fisheries: difficult now to estimate real impact of climate / over-catching activities!

8 Network of 17 meteo-ocean buoys (real time data available & free access for operational weather & ocean predictions) => Yearly cruises (mainly from Cotonou for the French eastern ones since 2005) Many oceanic measurements! (T(z), S(z), U&V(z), nutrients..) International programs: PIRATA PIRATA (Prediction & Research moored Array in the Tropical Atlantic) (1997 -???) Tripartite Programme as a contribution to CLIVAR, GCOS and GOOS : - FRANCE (IRD & Météo-France) - BRAZIL (INPE & DHN) - USA (NOAA/PMEL & AOML) Next yearly meeting in Brazil on March, 2010

9 PIRATA meteo-oceanic ATLAS buoys in open sea to monitor ocean/atmosphere conditions over the Tropical Atlantic

10 PIRATA ATLAS buoys: Measured Parameters : Atmosphere: - wind (direction, speed) - relative humidity - air temperature - precipitation - incident radiation Ocean: - temperature (11 levels from surface to 500m) - salinity (4 levels; 0,20,40,120m) - pressure (at 300 & 500m) - surface currents at 3 sites - Daily averaged data transmitted in real time by Argos; - High frequency data (10mn) available after servicing operations

11 Vandalism problems in the Gulf of Guinea due to fishing activities Total lost: about 11 buoys lost or damaged Lost of data, time, money, energy YFT ALB YFT ALB EU PS catches 2007 PS catches SKJ BET SKJ BET Example: fisheries effort in the GG in 2007 and 2008 (courtesy Alain Fonteneau, IRD)

12 Vandalism problem (fishers) in the Gulf of Guinea Ouidah, Benin, 2005; buoy from 10 W-Equator vandalized in 2003

13 Your attention please! SPECIAL MOMENT Pr A.K.Armah team and the pirata 10w-Eq atm sensors (March 2006) Many thanks to Pr A.K.Armah (DOF / GHANA) Officially AWARDED by the PIRATA International Scientific Steering Group

14 Example: The last PIRATA FR20 (2010) yearly cruise (45 days). Departure from Cotonou 1 calls at Cotonou 5 Atlas buoys + 1currentmeter mooring replacement T(z) profiles (XBT) & T,S,O2(z) profiles (CTD) + water samplings ARGO profilers (8) & surface drifters (3) SSS & SST L-ADCP at 10 W (10 S-1 30 N)

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16 Informations and data (free access) : Web sites: ftp://ftp.ifremer.fr/ifremer/ird/pirata/ + Cruises infos:

17 PIRATA ATLAS time series till Feb 10, 2010 east of 23 W: Eq-23 W: Eq-10 W: no pb from 2006, but winds Eq-0 E: no pb in 2009->(April 2010) 10 S-10 W: 6 S-10 W: 6 S-8 E: no pb during 1year test

18 International programs: 2) AMMA (African Monsoon Multidisciplinary Analyses) What is AMMA? A multidisciplinary and multiscale approach (+ international): Global: 2-way interactions between the WAM & the rest of the globe (e.g. role of SST patterns on WAM variability; impact of WAM on tropical Atlantic, export of aerosols/chemical species). Variability from seasonal to decadal scales Regional: Monsoon Dynamics and Scale Interactions, Continental Water Cycle, Land and Ocean Processes, Aerosols and Chemistry Variability from intraseasonal to interannual scales Mesoscale: Mesoscale Convective Systems, Vertical transports (Aerosols, Water, chemical species), Tropical Cyclones, Catchments and Vegetation Intraseasonal variability Sub-meso (<10km): Hydrological Cycle, Vegetation Convective rain scale=>coupling scale with hydrology (Sahel)=>Main scale of interest for agriculture, M O D E L L I N G S A T E L L I T E S O B S E R V A T I O N S ( important international program with planed continuation )

19 AMMA measurements network: atm, met, ocean, hydro, chem, From Lebel et al., 2009; AMMA measurements. LOP: Long Observation Period of Measurements EOP: Extended Observation Period of Measurements ( ) SOP: Special Observation Period of Measurements (2006)

20 Ocean in situ measurements : => 6 oceanographic cruises EGEE cruises, 2 per year in 2005, 2006 & 2007 => seasonnal variability (Egée1&2, 3&4, 5&6; early summer & fall) => interannual variability (Egée 1&3&5, Egée 2&4&6) => intra-seasonal (Egée 3) EGEE 1: June 7 - July 5, 2005 ; EGEE 3: May 24 - July 4, 2006 EGEE 5: June 4 - July 5, 2007 EGEE 2: September 1-30, 2005; EGEE 4: November 15 - December 2, 2006; EGEE 6: September 1-28, 2007 Mirror global AMMA DATA BANK at Niamey

21 Other measurements carried out in the framework of EGEE / AMMA: Measurements at São Tomé Island (0 N, 6 E) Meteorological Station (EGEE) + Tide gauge (PIRATA) 1) Installation of a meteorological station in October 2003 (data transmitted dayly by ARGOS satellite system) - DATA TRANSMISSION THROUGH THE GTS (from October 2006) - Autonomous thermometer ONSET installed in 2005 (=> SST) 2) Tide gauge maintained by IRD since 1980s. - Pressure, Atm. pressure + SST & SSS. - Part of GLOOS. - GPS positioned (in December 2002)

22 Links between the Atlantic Cold Tongue & West African Monsoon: STRONG LINK with regional water resources Mean June/July/August SST (averaged between 1998 and 2009) in the tropical Atlantic (a). Also included in (a) are the main surface (solid) and thermocline (dashed) current bands (see text for details). The white box in (a) defines the region for the ATL3 SST index shown in (b). Monthly SST residuals in (b) are calculated by subtracting the mean annual cycle; gray bars highlight boreal summer (June/July/August). The microwave OI SST dataset used here is available at From Brandt et al., 2010.

23 Some major results from EGEE/AMMA: June, June, June, Strong interannual signal of surface conditions (temperature)

24 Focus on the SST field differences Preconditionning phase: Wind Stress (source: ECMWF) differences in the west & impact on the thermocline slope in the east EGEE 1: June 2005: T(z) at 10 W EGEE 3: June 2006; T(z) at 10 W Marin et al., 2009

25 Focus on the SST field differences Existence of local wind bursts: Wind Stress (source: ECMWF) & impact on the cold tongue onset SST Differences around 0 E - Stronger wind stress in 2005 / 2006 till mid June - Wind event in May 2005 <=> cold tongue onset - Wind events (nearly 15d interval) in July-August 2006 => cold tongue onset in 2006 => less SST differences 2005 / 2006 from July. => importance of both remote & local wind forcing + wind bursts for SST in the cold tongue zone + minor importance of net heat flux for the cold tongue onset (not shown) Wind Stress Differences around 0 E Marin et al., 2009

26 Links between the Atlantic Cold Tongue & West African Monsoon: Onset date for the African Monsoon -WAM- (from Fontaine and Louvet, 2006; obtained using the GPCP data set) and onset date for the Cold Tongue -CT- (from Caniaux et al., 2010) From Brandt et al., Difference of Cumulative rainfall in Niger (Niamey) in : (early WAM and ACT, cold event) (late WAM and ACT, warm event) (intermediate situation). From Lebel et al., 2009

27 International programs: 3) TACE (Tropical Atlantic Climate Experiment) What is TACE ( )? International Programme as a contribution to CLIVAR-Atlantic: -USA (RSMAS, NOAA/AOML, several universities), GERMANY (IFM-GEOMAR), The NETHERLAND (KNMI), FRANCE (IRD) Mainly consists in the deployment of equatorial moorings around 23 W (Germany, France), 10 W (USA, France) and 0 E (USA), for the Equatorial UnderCurrent monitoring. => Dedicated cruises + long term time series of currents (+T, S, O2)

28 Germany; IFM-GEOMAR ADCP moorings ( )

29 Cruise track (2009) USA, RSMAS: PI: Bill Johns ADCP moorings ( )

30 TACE PIRATA-AMMA observing network in the Tropical Atlantic Network maintained by USA, Brazil, Germany & France

31 PROPAO could become an African contribution to the TACE PIRATA - AMMA observing network PROPAO Ripiecsa Ocean coastal network (see next presentations & discussions)

32 A few words about the 2010 rainy season case in West Africa: In Benin: About 60 deads, due to flood or house collapses; destroyed houses, More than sinistred people, More than out of houses, 40% of rice/horn production destroyed Cholera. (idem in Nigeria, Ghana, Togo!...). Extreme case!? climatic change? Gulfe of Guinea sea water warming? La Niña? Coastal cities flooded as rain water goes to sea With sea level rise => more flooded cities!

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34 T(z) Equatorial section from PIRATA ATLAS buoys (oct.2010) Positive T anomalies over The whole upper layers, + in the west at 100m depth

35 Long term trend of SST increase? => How about Sea Level?

36 Long term trend of SLA increase?

37 Climate changes <=> sea level rise and coastal erosion Cotonou, December 2009 & August 2010 (Photos: C.Duos & B.Bourlès, IRD) About 30m/year in some locations along the northern coasts of the GG Sea level rise Source: GIEC, 2007

38 Potential impacts of 1m sea level rise along the GG northern coast: Present level Ghana Togo Benin Nigeria Present level + 1 meter Most of the population + economy (ports) + agriculture (salt in the groundwater naps).

39 So what??? Importance of such climate/ocean studies & programs Importance of coastal observations & regional collaborations Importance of data sharing & common meetings Importance of capacity building Importance of communication!!! (for deciders & governments eg: coastal environment, management & cities, water resources, coastal agriculture )

40 CONCLUSIONS Continuity of research in oceanography beyond 2010 is critical for the region as a result of: - analysis and monitoring of oceanic conditions (temperature, salinity, sea level, currents, winds, nutrients ) - the influence of the surface oceanic variations on regional precipitations ; => Need to initiate urgent actions about: - Providing the requisite data and information for the management of marine fisheries resources (one of the main issues for the coastal countries) - Impact studies of oceanic conditions on climatic changes, resources and coastal erosion (sea level rise) associated to the present climatic changes...very important to the economic, social and political stability of countries in the region. -Maintaining and developping present coastal measurements networks (SST, tide gauges ).

41 FINAL REMARKS + STRONG NEED OF MORE COMMUNICATIONS - Data centers (in situ, satellite ) already exist (in Africa eg AMMA-, but also accessible for free through the web ) - Numerical results available (idem) eg numerical models exist in Africa (caution to: why, how, how and why are they built, which data used for forcing?) take care to black boxes using ) - African community has to be aware of all data access and funding opportunities (eg UEMOA, CEDEAO, ICSU, EU ) AND TO APPLY!!! (fundings available in the frame of climate change!). - Efforts of capacity building already exist (South Africa, Kenya, Senegal, Benin, Ghana ) and have to be reinforced! THESE ARE THE MAIN GOALS OF THIS COLLOQUIUM

42 MANY THANKS FOR YOUR ATTENTION