April 2013 – Open Malaria Warning

Temperature effects on the development rate and survival of two malaria vectors, and consequences for transmission

Yesterday an article by Lyons et al., “Stable and fluctuating temperature effects on the development rate and survival of two malaria vectors, Anopheles arabiensis and Anopheles funestus“, was published in Parasites & Vectors. This study is important to understand how climate change, changes in temperature between seasons, and from year-to-year influence the transmission of malaria. In this context it is interesting to see if the new data on Anopheles arabiensis alters the conclusion at which malaria is most efficiently transmitted. We refitted the egg-to-adult survival probability and mosquito development rate models described by Mordecai et al. with the data from the paper by Lyons et al., and calculated R0 according to temperature. While the old estimates for Anopheles gambiae s.s. suggested malaria is most efficiently transmitted at 25.6 C, the new data suggest malaria is most efficiently transmitted (by Anopheles arabiensis) at 25.7 C. The plot is showing transmission potential at the y-axis, and temperature in C at the x-axis. The red line is the estimate by Mordecai et al., while the black line is the estimate with the new data on Anopheles arabiensis.

Does Northern Hemisphere volcanic eruptions influence Sahelian rainfall?

In a recent study in Nature Climate Change Haywood and colleagues demonstrate how volcanic eruptions can influence Sahelian precipitation. Sadly the article is not open access, but from the abstract it seems like they are providing further evidence that aerosols are important for rainfall in the Sahel. In this context I also recommend the study by Huang which shows how black carbon also is a player in this game.

Haywood and colleagues suggest that sporadic volcanic eruptions in the Northern Hemisphere cause Sahelian drought. Using de-trended observations from 1900 to 2010, they show that three of the four driest Sahelian summers were preceded by substantial Northern Hemisphere volcanic eruptions. They used a state-of-the-art coupled global atmosphere–ocean model to simulate both episodic volcanic eruptions and geoengineering by continuous deliberate injection into the stratosphere. In either case, large asymmetric stratospheric aerosol loadings concentrated in the Northern Hemisphere were a harbinger of Sahelian drought whereas those concentrated in the Southern Hemisphere induce a greening of the Sahel.