Research project CG/DD1/10 (Research action CG)
Context
The influence of El Niño stretches across the Indian Ocean towards Africa, where it causes droughts in southern Africa and inundations in equatorial and eastern Africa.
The 1991-92 El Niño event caused the worst drought of this century in southern Africa, affecting nearly 100 million people (Cane et al., 1994). In Kenya, Sudan, Uganda and several other neighbouring countries, abundant floods were observed during the 1997-98 El Niño event. ENSO (El Niño/Southern Oscillation) indices are now used in East and Southern Africa for rainfall prediction (WMO-UNDP, 1993, IPCC, 1990).
In eastern Africa, climate variables such as air temperature, atmospheric pressure, and rainfall, and fisheries are correlated with ENSO, as are monsoon winds, which influence lake hydrodynamics and nutrient contents of surface water such as for Lake Tanganyika. Models are being developed that allow a timely prediction of the onset of ENSO phenomena. Understanding of the influence of ENSO in the region will help to predict ENSO induced changes in the limnological environment and productivity of Lake Tanganyika, and to predict the potential crop production in the region.
Lake Tanganyika, one of the oldest lakes in the world, is very sensible to climate variability. Its sediments might prove to be real archives of paleo-climatic variability, reflecting changes in sea surface temperature and monsoon regimes in East-Africa. If the ENSO signal can be understood from recent data, its possible recording in the sediments of this 10 to 20 million years old lake could be of world interest. Comparing the recent signal with the signal recorded in the sediments may contribute to a better understanding of the human impact on the recent climate change.
Objectives
The PROJECT aims at a better understanding of the impact of ENSO phenomena on Lake Tanganyika and the surrounding region in the recent past. The sediments of Lake Tanganyika are studied for the last 1000 years, analysing the relationship with inter-annual climate variability and possible links with ENSO in East Africa. Lake Tanganyika is one of the oldest (more than 10 million years old) and deepest lakes of the world (1470 m). It has been chosen for its high potential in recording paleo-climate signals due to the favourable anoxic environment of its deep waters.
Methodologies
The 4 research teams envisage an integrated multi-disciplinary approach. Two teams are studying the recent phenomena, which occurred over the last 30-50 years, while the two other teams investigate the recording of paleo-climatic signals in the sediment cores collected in Lake Tanganyika.
Partners
1) Recent ENSO
The teleconnection study is a statistical approach to study the remote correlation between time series of climate, fishery and agriculture data on the one hand and the ENSO indices such as sea surface temperature and southern oscillation index on the other hand. It is realised by: Musée Royal de l'Afrique Centrale
The remote sensing study is based on the analysis of a time series of low-resolution remote sensing data acquired over the study area between 1981 and 1994. (Study of the lake and its surroundings: upwelling intensity, vegetation index, sea surface temperature, land surface temperature...). It is realised by Laboratoire de Télédétection et d'Analyse Régionale (UCL).
2) Paleo-ENSO
A sampling expedition took place at Lake Tanganyika. The collected cores are analysed by two teams. The Sedimentology study (dating, sedimentation rate, calcium carbonates, image analysis...) is realised by Unité de Paléontologie et Paléogéographie (UCL).
The very high-resolution study of diatoms and chrysophytes cysts on laminated parts of the cores is performed by Laboratorium Plantkunde (RUG)
Deliverables and expected results
Recent ENSO:
Teleconnection maps have been established based on climatic and remote sensing data. They allow investigating the impact of ENSO on the climate and the vegetation performance in different parts of eastern Africa and this for varying time lags.
The impact of extreme climate conditions (El Niño, La Nina) on the lake and on the thermal structure of the water column will be simulated. On the one hand those data will be used for the interpretation of paleo-climatic data and on the other hand to investigate the possibilities to develop forecasting models for the fishing in Lake Tanganyika, the latter being of considerable importance in East Africa (200 000 tons per year).
We will test whether the applied methodology can be used in studies concentrating on recent or ancient climate variability, involving longer time periods or larger areas. Homogeneous zones that react to partially predictable climate variations in general and ENSO effects in particular will be identified.
Paleo-ENSO:
The inter-annual variation in the productivity and composition of diatom algae and the structure of sediments is studied. Hypotheses will be formulated for a paleo-climatic interpretation. Cyclic variability that might correspond to ENSO cycles (3-7 years) will be analysed. If the ENSO signal can be identified, a comparison will be made of the recent variability with the variability that occurred over the last 1000 years. This will allow investigating the possible human impact on recent changes in the natural variability of the climate (objective of the research for a sustainable development). We will also investigate the feasibility of a study of paleo-ENSO going back further in time than 1000 years.
