4A.3
West Africa Desert Locust infestations: connections with regional atmospheric circulation patterns
Chiara Vallebona, CNR, Firenze, Italy; and A. Crisci, A. Di Vecchia, L. Genesio, G. Maracchi, and M. Pasqui
Desert Locust (Schistocerca gregaria [Forskål]) infestations threaten many African, Middle East and Southwest Asian countries. This grasshopper has the aptitude to undergo a density-dependent solitary to gregarious phase-transition called gregarization, characterized by high level of activity, mobility, cohesion and persistence of populations.
An infestation is likely to originate when gregarization is accompanied by a marked build-up of population numbers from generation to generation, occupying an expanding area. Scientific community effort was spent to investigate on insect's biology and ecology, especially concerning breeding, distribution and gregarization.
The role played on Desert Locust infestations by proper environmental conditions or local meteorological events (i.e. rainfall) is widely accepted and few authors have suggested Desert Locust population dynamics to be driven by synoptic climatic factors.
The potential of depicting the typical atmospheric circulation feature forcing West Africa Desert Locust infestations is undoubted since it would be the base to implement operational early warning systems.
Specifically, historical data series on infestations were prepared by integrating several sources; an exploratory statistical analysis was then carried out on a monthly basis covering the 1979÷2005 temporal window on zonal wind cross sections (1000÷100 hPa and 0º÷20ºE) from NCEP-DOE Reanalysis 2 dataset, with a 2.5º spatial resolution. Both parametric and non parametric bootstrap tests were used in order to establish whether West Africa Desert Locust infestation onsets presented some statistically significant difference with respect to recessions. The analysis suggests a significant role of a weaker easterly flow during spring on West Africa Desert Locust infestations, since significant positive anomalies of zonal wind do exist centered at 10º÷15ºN and at 700÷500 hPa, as well as the African Easterly Jet core (AEJ). This weaker than normal AEJ, during spring time, seems to be a major triggering mechanism for potential locust population dynamics change along with westerly wet air advection. Such AEJ anomalous occurrence, which is a basic circulation characteristic for tropics, guarantees the physical link between large and local dynamics. This conjecture it is found to be statistical significant.
Recorded presentationSession 4A, African Climate: IV. West Africa
Monday, 21 January 2008, 4:00 PM-5:30 PM, 215-216
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