Frequency distributions of chikungunya outbreak events in relation to precipitation.

<p>Frequency distributions of chikungunya outbreak events and 4-month cumulative precipitation anomalies for East Africa (A), Central Africa (B), South Asia (C), and Southeast Asia (D). The 4-month anomaly threshold was used to represent periods of either persistent above-normal rainfall/wetness or persistent drought conditions. The dashed line at zero depicts the (1979–2009) long term rainfall, with greater-than-normal precipitation shown to the right (blue) and lower-than-normal precipitation shown to the left (red) of the line. Cases shown to the left of the dashed line occurred during periods of drought with a persistence of 4 months.