ИСТИНА

This article presents the results from long term-aerial photographs and -monitoring gully head-retreat during almost the entire 1959 - 2015 period in different parts of the Udmurt Republic. It was determined that gully head retreat rates (GHRR) decreased from 2,4 m yr-1 to 0,3 m yr-1 for the 1959 - 1997 observation period and the 1998 - 2015 period, respectively. Measurements of gully head-retreat were made once per year for most of the monitoring sites and twice per year (after snow-melt in May, and after the rainy season (October-November)) for gullies located in the Eastern part of the study area that contain high proportions of arable land. 80% of GHRR occurred during the snow melt period (1978-1997), and decreased to 53% since 1997. Spatial patterns of changes of GHRR resulting from changing hydro-climatic factors for the different regions of Udmurt Republic as a whole were determined from the analysis of data collected at 6 meteorological and 4 hydrological stations. The main reason for decreasing GHRR appears due to reductions in winter frozen soil depth. The influence of stormwater runoff more clearly occurred within the East and North parts of Vyatka-Kama interfluve, whereas higher correlation between GHRR and frozen soil depth was found for the west parts of the Republic. The most significant increases in gully length appear to have occurred during the warm part of the year (June-July), after >40 mm rain-storms.