Testing two different precipitation datasets to compute the standardized precipitation index over the Horn of Africa

Severe droughts are a frequent problem for the Horn of Africa. In this article we test the possibility to use the Standardised Precipitation Index (SPI) for monitoring the availability of lack of precipitation in this region. The SPI is a statistical indicator evaluating the lack or surplus of precipitation over different time scales, thus allowing to distinguishing time-related impacts of the moisture deficit. SPI is calculated as a function of the long-term average precipitation, using continuous, long-term series of historic accumulated monthly precipitation records. The SPI for a given rainfall amount is then given in units of standard deviation from the mean of an equivalent normally distributed probability distribution function. As a consequence, wetter and drier climates and periods can be represented and monitored in the same way. For this study, the 3, 6, 9 and 12 months SPI has been calculated for the period from 1985 to 2008 over the Horn of Africa using GPCC and ERA-40 data interpolated to a 0.25 degree grid. Both SPI datasets have been compared for selected time periods by means of root mean square error, correlation coefficient and contingency tables approach. First results demonstrate the feasibility of using SPI for drought monitoring at regional scales over Africa.JRC.H.7-Land management and natural hazard