Hydrological response to meteorological drought using the Palmer drought indices in Thessaly, Greece

This study evaluates the efficacy of Palmer drought indices to monitor hydrological droughts in river discharges and soil moisture in selected watersheds with varying geomorphologic characteristics in region of Thessaly, Greece. The Palmer four indices (PDSI, Weighted PDSI, PHDI and the moisture anomaly Z-index) were used as indicators of meteorological drought severity. The hydrological drought severity was evaluated from the outputs of the monthly UTHBAL conceptual water balance model. The UTHBAL model was calibrated with the available observed runoff data to extend, reconstruct and produce runoff and soil moisture timeseries for the hydrologic period 1960–2002 at the study catchments. The produced hydrologic variables were normalized through Box-Cox transformation and standardized to normal distribution. The standardized hydrologic variables were used as an indicator of hydrological drought severity and were compared with the Palmer drought indices timeseries estimated by basin-wide meteorological data. The results showed that, in general, the Weighted PDSI and the moisture anomaly Z-index were found to better represent river discharges and soil moisture, respectively, for all study watersheds irrespectively to their area, geophysical, and hydroclimatic characteristics. However, the results were quite variable in the identification of specific historical drought periods. Although, the Palmer indices were successful in the identification of drought severity of historical events, they failed to identify the drought duration.