Quantification of monthly meteorological droughts: Comparison of four indices in three locations of San Luis Potost, Mexico

Meteorological droughts are temporal recurring events that cause a lack of precipitation. They are a feature of all climates and are, perhaps, the most complex natural hazard due to their slow evolution, which renders their opportune detection quite difficult. In this work, four indexes for monthly drought detection are contrasted, classifying them as light, moderate, severe and extreme. Such indexes are: (1) modified deciles index (MDI), (2) the statistical Z index Z (SZI), (3) the China Z index (CZI) and (4) the standardized precipitation index (SPI). The above-listed indexes are applied to monthly precipitation data in three climatological stations with large records (>= 50 years), which represent the three dissimilar climates of the state of San Luis Potosi, Mexico. Twelve durations of droughts were analyzed, ranging from one to 72 months and processing of the rainfall information was performed with the technique of moving sums. The study results showed that the MDI and SZI indexes are not recommended, because their estimates have anomalies. The results of the CZI and SPI indexes are largely similar and free of defects; therefore, their systematic application is recommended. Based on results of the CZI and SPI indexes, the percentages of each type of drought are set in the three records processed. With the results of SPI, its evolution graphs are formed and with them the temporal characteristics of drought are defined; also, the total number of droughts, of each duration, is estimated in a lapse of 100 years.