This Analysis tool allows users to view different presentations of the the most recent dekad. The default map on this page displays dekadal (approximately 10-day) rainfall amounts over the country. The default map shows rainfall totals for the most recently available dekad, but totals for previous dekads can be displayed as well. By clicking a location on the map, the user can generate four time series graphs that provide analyses of recent rainfall averaged over an administrative district, with respect to that of recent years and the long-term mean.
The rainfall Anomaly map displays the difference between the most recent dekadal rainfall and the long-term average (from 1983 to 2012). Positive (negative) values indicate dekadal rainfall that are above (below) the long-term mean or climatology.
Standard Precipitation Index (SPI)
The SPI map displays the standard rainfall index of the most recent dekadal rainfall (using 1983 to the latest complete year as base period). The SPI (McKee 1993) is the number of standard deviations that observed cumulative rainfall deviates from the climatological average. To compute the index, a long-term time series of rainfall accumulations over dekads are used to estimate an appropriate probability density function. The analyses shown here are based on the Pearson Type III distribution (i.e., 3-parameter gamma) as suggested by Guttman (1999). The associated cumulative probability distribution is then estimated and subsequently transformed to a normal distribution. The result is the SPI, which can be interpreted as a probability using the standard normal distrubtion (i.e., users can expect the SPI be within one standard deviation about 68% of the time, two standard deviations about 95% of the time, etc.) The analyses shown here utilize the FORTRAN code made available by Guttman (1999). Places where the dekadal climatology is less than 2 mm are masked out.
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