نوسانهاي وقوع باد و روزهاي طوفاني طي نيم قرن گذشته در منطقه خزري

Thunder and storm fluctuations in the Caspian region over the last half century

Thunder and storm fluctuations as consequences of climate change were studied in the Caspian region over the last half century. In this study, whole forest areas in southern part of Caspian sea were monitored by study on vegetation map and field visit. Three points representing the major part of the Hyrcanian forests were selected from wet part in the west to drier part in the east. Four meteorological stations data used for investigation. Most of climatic factors including maximum, minimum and mean annual temperature; daily, monthly and annual precipitations were investigated . Numbers of days with thunder and storm as well as wind speed were used for conclusion. During last half century, as eon sequence of climate change by means of increasing temperature and changing precipitation trends, number of Days With Thunder and Storms (DWTS) inereased in forest area in the Caspian region. In Rasht and Gorgan stations, the number of days with thunder and storm in last half century, especially in last 25 years showed a sharp increase. This is in the same line of increasing mean annual temperature about 1.28°C and minimum temperature about 2.45°C in Rasht station . In addition, it is against the decrease of precipitation for the period of last 5] years in Gorgan station which is about 55.6 mm. Anzali and Baboulsar stations which arc under coastal climate condition have a fluctuating trend of DWTS but also showed a mild increase in the trend of DWTS during last fifty years. This is in favor of increasing the mean annual temperature in Baboulsar station in last 54 years, about I.44°C and its minimum temperature about 1.80°C. Also again, it is against the decrease of annual precipitation in Anzali station during last 54 years of records, which is about 409.4 mm and amount of the decreas of precipitation for the period of last 5] years in Gargan station is about 55.6 mm.