application of reservoir level and meteorological indices for drought monitoring (case study: zayandeh rud water system)

drought is among the natural disasters that causes heavy damages to water resources and makes managers face serious challenges. drought monitoring is one of the important measures to manage droughts. different indices and methods employing varied indicators, have been developed in this regard. in this paper it is aimed to compare two well known meteorological indices of spi and edi with a hydrological method, based on reservoir level, to monitor drought in the zayandeh rud water system. towards this, the 1998-2001 droughts, as the severest drought spells within the recorded data are applied for the evaluations. the results indicate that each of the methods has its own capability that can be helpful for water managers. therefore, a simultaneous application of the indices is emphasized. as for the study area, the results suggest that spi works well for drought onset and early warnings. the hydrological approach is found as more relevant during the drought, when operational measures should be implemented. finally, it is edi that responds more slowly to precipitated rainfall and more safely pronounces the drought end.