Differences in spatial patterns of drought on different time scales: An analysis of the Iberian Peninsula

The differences in spatial patterns of drought over a range of time scales were analysed by the Standardized Precipitation Index (SPI). In a climatic area with a wide range of precipitation characteristics (the Iberian Peninsula), Pearson III distribution is flexible enough to calculate the drought index on different time scales. The Pearson III distribution was adapted to precipitation frequencies at time scales of 1, 3, 6, 12, 24 and 36 months. Spatial patterns of drought were analysed by Principal Component Analysis. The number of components found increased as the time scale did, which indicates great spatial complexity in drought analysis and uncertainty in drought classification, mainly at scales of 24 or 36 months, since the relationships between SPI series of observatories becomes more distant as the time scale increases. We concluded that there were no homogeneous regions with similar drought patterns that could be used for effective drought management or early warning.