Impact of changing climate on thawing and snowmelt-driven gully erosion in Eastern Romania

Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to better understand gully development by providing quantitative information from long-term field measurements in small catchments over a 60 year period (1961-2020). Several methods were used to accurately measure and estimate gully growth.

Intense gully erosion has sculptured remarkable landforms around the town of Barlad. The permanent gully systems consist of two main gully types, discontinuous and large continuous gullies in valley bottoms. The discontinuous gullies are associated with small catchments (usually <100 ha in area) and ephemeral peak runoff discharges are usually ≤2 m³ s^-1.

Fourteen representative continuous gullies were selected, most of them having catchment areas <500 ha. Linear gully head retreat and areal gully growth rates were quantified for six decades. The results obtained indicate that gully erosion rates have decreased since 1960s (i.e. 19.5 m yr^-1 linear gully head retreat) to 3.2 m yr^-1 during last decade.

Gully growth is believed to be mainly triggered by severe rainstorms and resultant runoff events. However, the impact of late winter (especially thawing and snowmelt runoff) on gully development is often overlooked.  Mean annual air temperature at Barlad (Romania) is 10.2^oC and means annual precipitation is 508 mm (1961-2020), of which 35% falls during the cold season (October-March). Multiple annual field measurements on the growth of six continuous gullies between 1981-2000 indicate that half of the mean gully growth occurred in the cold season (in late winter, mainly in March).Based on data collected from different locations in the temperate zone of the Northern Hemisphere, it is possible to postulate that the relative contribution of the cold season to the gully development is highly variable and is closely related to climatic conditions. Thus, the contribution is very small in north-east China, ~25% in western Iowa (USA), ~50% in the Barlad Plateau (eastern Romania) and ~67% in the Middle Volga region (Russian Federation).