Objective: Due to their adverse consequences and increased frequency in recent decades, extreme precipitation events have doubled the importance of identifying their synoptic-thermodynamic patterns for managing and reducing losses. Heavy precipitation is one of the most important climatic hazards in Lorestan Province, which has increased in recent decades in the context of climate change. This study aimed to reveal and compare the synoptic-thermodynamic patterns of seasonal heavy precipitation in Lorestan Province, which is considered one of the main centers of these climatic hazards.
Methods: Daily precipitation data, synoptic factors from the NCEP/NCAR database, and upper atmosphere data from the University of Wyoming were used. Using the 95th percentile method, heavy rainfall events were identified, including one autumn event (November 17, 1994), two spring events (April 14, 2016, April 1, 2019), and two winter events (January 9, 1999, and February 3, 2006) during the period (1994-2020).
Results: In the autumn, a deep trough over the eastern Mediterranean and western Iran, along with low-level low pressure, and moisture supply from the Mediterranean, Black Sea, Red Sea, and Persian Gulf, through cyclonic and cyclonic centers, causes torrential rainfall. Spring patterns were similar to autumn, including a deep Mediterranean-Iranian trough and low-level low pressure, along with moisture supply from the Oman and Arabian Seas by the cyclonic center. However, in the winter, the establishment of a low-altitude blocking system truncated in the middle atmosphere provides conditions for heavy rainfall.
Conclusions: The main cause of heavy precipitation is not necessarily large storms in the upper atmosphere, but the lower levels can also play an important role.