Current conditions in Iran and the world are such that water scarcity in most regions is gaining increasing importance day by day. In this context, consecutive droughts have caused the true value of these resources to become ever more apparent. In the present research, a dynamic simulation of meteorological drought was conducted in the upstream area of the Sefidrud in East Azerbaijan Province. To accurately assess daily drought using the Effective Drought Index (EDI) method, all 10 existing stations in the region from 1996 to 2024 were investigated. The results indicated that no extreme drought has occurred in this region. However, severe drought has occurred at most stations in the area, with higher intensity during the years 2002-2004 and also in 2011. At the severe drought level, the highest number of dry days was recorded at Chapini station with 237 dry days in 2002. Correspondingly, Kuhsalar station reported the year 2011 with 170 severe dry days. Moderate drought has occurred at all stations. The years 2002 and 2004 showed moderate drought at most stations. Among these, Alavi station had the longest sequence of dry days at the moderate level in 2004, with 312 dry days recorded. Wet or normal conditions have also been reported at all stations. The year 2013 was declared a wet year at most stations. Mianeh station experienced the maximum number of non-drought (wet/normal) days, reporting 354 days. Additionally, Qeshlaq station declared the year 2015 a normal year with 359 wet days reported. In most stations in the region, the years 2013 and 2015 were declared wet years. However, Ahar station declared the years 2018 and 2019 as normal or non-drought years, with 357 and 346 days recorded, respectively. This same station also reported the year 1999 with 45 days of severe drought. This station is the only one that reported severe drought. Subsequently, for more detailed investigation and determination of drought severity, daily variations of the EDI drought threshold were examined at all stations. For example, at Ahar station, in the years 1998 and 1999, with recorded minimum thresholds of -2.19 and -3.051 respectively, severe and extreme drought were reported. During these years, this station experienced 326 days at the moderate level, 264 days at the severe level, and 45 days at the extreme drought level. During the years 2001 to 2005, moderate drought had greater continuity, and in the years 2002 and 2005, with recorded values of -2.56 and -1.71 and 122 and 16 dry days respectively, it also reached the severe level. Furthermore, the years 2011 and 2012 were also at the moderate level with recorded minimum values of -1.55 and -1.56 and 2 and 18 dry days at the severe level, respectively. As can be seen, the drought level changes even with the recording of 2 dry days. It is noteworthy that daily variations show that recording even one dry or very dry day can indicate drought, but the sequence of dry days is also of great importance because the continuity and sequence of drought is more critical than the existence of a single dry day and requires a longer duration. Also, at Mianeh station, the years 2002 and 2004, which have the longest sequences of dry days, experienced the minimum threshold values of -2.20 and -2.15, respectively. The drought threshold in 2024, at -2.01 over 56 dry days, recorded severe drought. The continuity of dry days is highly variable, and even if a severe threshold occurs over 5 days (year 2000), the drought level changes. Therefore, simultaneous examination of the number of consecutive dry days alongside the minimum threshold is of high importance. According to the aforementioned figure, the highest number of dry days at the moderate level in the years 2003 and 2012 shows 206 and 202 days with thresholds of -1.44 and -1.36, respectively. Also, similar to most stations in the region, the year 2013 had the highest number of wet days with a figure of 354 days. Extreme drought was not recorded at this station. At this station, the recorded figures indicate the occurrence of moderate and severe drought, but what is important is the number of days a given level has prevailed. Finally, the results show that the region has not experienced extreme drought and has mostly had moderate and severe drought.
