Home – Home – Jornals – Geography and Natural Resources 2020 number 4

Presented are the results from investigating the synoptic processes observed during the floods in the south of Irkutsk region (June 20-30 and July 25-30, 2019). A comprehensive synoptic analysis was conducted to identify the main causes of extreme high precipitation amounts in the area of Tulun and Nizhneudinsk in summer 2019. During June 25-29, the southern areas of Irkutsk region showed heavy and very heavy precipitation, with its amounts within 31-81 mm in 12 h, as well as long-lasting heavy precipitation (136 mm in 36 h). The maximum rainfall was observed in the territories of Nizhneudinskii (106-140 mm) and Tulunskii (85-218 mm) districts, which amounted to 1.5 and 4 normal monthly values, respectively. It was established that the main factors determining intensity of the catastrophic floods were: 1) a powerful truncated cyclone; 2) a blocking trun cated meridional ridge over Eastern Siberia; 3) a slow-moving cold atmospheric front, 4) advection of contrasting air masses to the study area (warm subtropical and cold and humid masses from the south of Western Siberia, and easterly masses ones from the coast of the Sea of Okhotsk). The aforementioned directions of the transport of air masses were determined by analyz ing the HYSPLIT 5-day backward trajectories. Foci of high content of potentially accumulated moisture and fields of upward vertical air movements were identified over the study area. An intensification of the frontogenesis and an enhancement of pre cipitation could be caused by local orographic features contributing to the formation of orographic upward vertical flows, gave rise to a forced convection in the foothill areas. It is concluded that the two flood events were forced by precipitation of fron tal origin.