Description:  These plots indicate the standardized 12-month WASP index. Shading starts at +/- 1 with green shades indicating unusually wet conditions and brown unusually dry, respectively. Regions with an annual average precipitation of less than 0.4 mm/day have been "masked" from the plot.

WASP is an acronym for the "Weighted Anomaly Standardized Precipitation" index. The index is computed by first computing monthly precipitation anomalies and then standardizing them by divivding by the standard deviation in monthly precipitation over the base period 1979-present. The standardized monthly anomalies arethen weighted by multiply the fraction of the average annual precipitation for the given month. These weighted anomalies are then summed over th 12 month period ending on the date indicated on the plot.