Extreme Exogenous Processes in the Ukrainian Carpathians

Abstract

In the Ukrainian Carpathians hydrometeorological and topographical conditions jointly control the geographical distribution of exogenous geomorphic processes. In the region, channel-forming floods occur at daily precipitation intensities of 40–60 mm. Maximum daily amount of precipitation reached 160 mm in 1992 and caused rapid water level rises up to 8.5 m. Similar floods with catastrophic effects happened in 1947, 1957, 1969, 1970, 1980, 1998, and 2001. The main causes of the November 1998 and March 2001 floods were natural hydrometeorological factors reinforced by considerable human impact over the last decades. For landslides 5-year cycles and for mudflows 11-year cycles are observed. Seismic activity also influences landsliding in the Ukrainian Carpathians. The risk of extreme devastation by mudflows is also very high. For dangerous mudflows the precipitation threshold is 30 mm day−1, while disasters only ensue from rainfalls above 100 mm day−1 intensity. Types and drivers of movements are identified. During extreme flash floods, significant changes in riverbed morphology have been observed (bank erosion, channel incision, and sediment accumulation). Bank retreat along the Tysa River, particularly at the confluences of major tributaries, reaches rates of 1 m year−1 (for the Tereblia confluence even 5 m year−1).