Karst Spring Discharges Analysis in Relation to Drought Periods, Using the SPI

Based on the long hydrological time series, the correlation between karst spring discharge series and rainfall has been analysed, using the Standard Precipitation Index (SPI). Analysis has been focused on the drought periods. Data come from a large karst system (Campania, Southern Italy), in an area characterised by a distribution of the precipitation prevalently during autumn-winter period. Insufficient recharge due to poor rainfall results in flat spring hydrographs (with no peak during spring season) that indicate a continuously decreasing discharge. Specifically, it has been found that 12 months cumulative rainfall, expressed by SPI12, and spring discharge have similar trend. When SPI12 will be equal or less that -aEuro parts per thousand 1, springs reduce the discharge, and a flat spring hydrograph will be produced when SPI reaches value less than -aEuro parts per thousand 1.5. In these cases, the prolonged shortage of accumulated rainfall causes a reduction in spring discharge also during the following year as well, pointing out a memory effect of the karst aquifer, and more complex rainfall-discharge relationship is observed.