This article presents results from the long term-monitoring of
gully headcut retreat rates (GHRR) between 1959 and 2015 in different parts
of the Udmurt Republic and is based on the use of historical aerial
photographs and field observations (measuring the distance from the gully
head to a fixed reference point) (Vanmaercke et al., 2016). It was determined that GHRR decreased from
2.4 to 0.3 m yr
Map of the Volga River basin showing the location of the Vyatka-Kama
interfluve
Gully erosion is an important soil degradation process in the southern half of the Russian Plain. The dissolution of the USSR at the end of the 20th and beginning of the 21st century led to significant changes in land use in forested areas, including the taiga and broad-leaf forests; large areas of arable land were abandoned. These changes coincided with global warming during the last decades of the 20th and early 21st centuries. Recent decades have been characterized by significant climatic changes that resulted in substantial reductions in surface water runoff in the European territory of Russia (ETR) and Western Siberia (Bazhenova et al., 1997; Dedkov, 1990; Petelko et al., 2007).
The research area is located in the Eastern part of the Russian Plain in the
southern part of the Vyatka-Kama interfluve (Fig. 1). This area of the Udmurt
Republic is located south of the taiga zone. Elevations in the study area
are in the range of 120–250 m a.s.l. with maximum relative elevations
occurring along the river valleys. This area of the Udmurt Republic is
characterized by a temperate continental climate with annual precipitation
in the range of 550–600 mm; mean annual temperatures in January and July are
Gully erosion was studied by using two approaches. Firstly, high resolution
aerial photographs (surveys 1959, 1970 and 1980) were used for evaluation of
mean annual GHRR for the 1959–1970 and 1970–1980 periods; we used images
with scales of
Mean annual gully head retreat rates for different time intervals within Udmurt Republic (time intervals 1959–1970 and 1970–1980, based on aerial photograph comparisons; time intervals 1978–1997 and 1998–2015, based on monitoring data).
The mean annual gully head retreat rates for the period 1978–2015, based on results of the field monitoring of gully heads at 28 sites (for site location see Fig. 1) (Legend: 1 – mean annual rates; 2 – mean rate for five-year periods).
The mean contribution (in %) of snow-melting and rain-storms in annual gully head retreat rates for periods of monitoring 1978–1997 and 1998–2014 (Legend: 1 – period of snow-melting; 2 – rain-storms period).
Annual contribution (in %) of snow-melting and rain-storms in annual gully head retreat rates for the period 1998–2014 (Legend: 1 – period of snow-melting; 2 – rain-storms period).
The mean gully head retreat for gully catchments with “warm” and “cold” aspects for the periods 1978–1997 and 1998–2015 (Legend: 1 – gully catchment with “cold” aspects (N, NE, NW and E); 2 – gully catchment with “warm” aspects (S, SW, SE, W).
It is important to note that the monitoring period for GHRR coincided with
climate warming, which began during the second half of the 1970s (Rysin,
1998). Based on aerial photographs, the mean linear GHRR decreased from 2.4 m yr
There has been a considerable decrease in the mean annual rate of linear
GHRR since 1997 (Fig. 3). During the 1978–2015 observation period it is
possible to identify 3 peaks, with maximum values occurring in 1979 (2.8 m yr
Based on the results of the first monitoring phase of this study (1978–1997)
it is possible to conclude that 81 % of linear GHRR occurred during the
snowmelt periods between March and April (Fig. 4), with the remainder
occurring during the warm season. The second monitoring period (1997–2015)
was characterized by a sharp decline in the mean linear GHRR (0.3 m yr
The main reason for the substantial reductions in gullying since 1997 appears to be increasing winter air temperatures due to global warming. This led to substantial reductions in surface water runoff from the surrounding slopes during snowmelt because of an increasing frequency of years where the frozen soil depth was < 40–50 cm. The impact of snowmelt for annual GHRR appears to have declined by some 53 %, with relatively high interannual variations (Fig. 5). It also is important to note that during the warm part of the year, serious GHRR occurred in conjunction with intense rainstorms where precipitation exceeded 40 mm. The maximum number of such rainstorms were observed within the Vyatka-Kama interfluve between 1990–1994. Since 2003, the number of extreme rainstorms (> 40 mm) has declined in the study area (Rysin et al., 2017).
There is reason to believe that GHRR also depends on slope aspects relative to solar radiation. For the observation period, most gullies developed on the slopes that favored cold aspects (North, North–East, East, North–West; Fig. 6). In fact, the overall water resulting from snowmelt on the southern slopes is lower than on the northern slopes, where evaporation is relatively low. Also, during the second monitoring period (1998–2015), there was a noticeable reduction in GHRR for the slopes with cold aspects. The reason for this decrease probably is an increase in March temperatures during snowmelt.
Finally, it is possible to conclude that a limited number of factors influenced mean annual GHRR between 1959 and 2015, these include: land use changes, declining gully catchment areas, and climate warming. However, the latter factor appears to have led to the most notable declines in mean annual GHRR after 1996. A positive trend in mean annual GHRR has been observed for bottom gullies within the Vyatka-Kama interfluve area after 2006, and may be the initial indicator of some changes in the conditions of surface and subsurface runoff within the gullied catchments.
The paper used data from a united database of gullies in the territory of the Republic of Udmurtia (Vanmaercke et al., 2016). Also we used of the database of gullies of the Udmurt Republic data, which is patented in Russia.
The authors declare that they have no conflict of interest.
The work was funded by Russian Scientific Fund, project no. 15-17-20006.