Flood hazard on the rivers of the Northwestern Caucasus by spatial analysis according to precipitations and level observations in 2014–2020

Abstract

The rivers of the North-Western Caucasus, despite the flood regime of runoff, until 2013 were not covered by regular observations of the water level. The network of automatic level gauges accumulated level observations every 10 minutes in 2014–2020. Spatial analysis tools were used to calculate the distribution of flood runoff velocities and the distribution of water runoff time on watersheds. Histograms of the distribution of watershed areas of level gauges by travel time were obtained and hydrographs for extreme precipitation were calculated using the example of July 6–7, 2012 in Krymsk. In the water level observation data, periods of level growth of more than 20 cm, accompanied by intense precipitation—4110 flood events at 69 level gauges, were identified. Flood cases are divided according to level growth into groups: up to 0.5 m, up to 1.0 m, up to 2.0 m and more than 2.0 m. The distribution of maximum daily precipitation according to ERA5-Land data for the watersheds of level gauges is considered. The calculated discharges and observations of the level showed that the highest discharges and high and frequent flood levels are observed on the rivers of the northern macroslope of the Caucasian watershed—rivers Abin, Shebsh and Pshish. On the southern macroslope, rivers are distinguished. Mezyb, Vulan, Pshada, Shapsho and Dzhubga, however, they are inferior to the watersheds of the northern macroslope. The scale and number of flood level rises in the northern watersheds (left tributaries of the Kuban River) increases from west to east and in accordance with the growth of the watershed area. In the southern watersheds, the trend is similar, but due to smaller watersheds in general, less noticeable. The highest value of the ratio of the maximum discharge to the total runoff is observed in the smallest watersheds, i.e. the most sudden floods are observed on them, however, due to the small catchment area, they do not form dangerous flood levels. A small number of flood events in the watersheds of the western part of the region is due to the nature of precipitation in 2012–2020 and small areas.