Farmland damage speed and development stage of gully erosion in typical black soil region from 1970 to 2021

Gully erosion in black soil region can destroys destroy the farmland and to threatens threaten the grain production in the black soil region of China. Studying tThe development speed, current situations and trends of gully is can be exploredof great significance to reveal the mechanism of gully erosion and protect for the black soil. This study aims Tto investigate the rate and development characteristics of gully erosion damage to the cultivated land in north China over the past 50 years, . nNine farmland watershed units of farmland totaling were selected as the total areas of 378 km² with the average slopes of 1%, 2%, and 3% were selected in the three latitudes of typical black soil region, . The unmanned aerial vehicle (UAV) and ground measurements were combined with and the satellite images in 1970, 2011, and 2021 combined with . UAV and ground measurements were used to study the The damage speed of farmland was then determined by gully development. The results showed that the number of gullies were continued to increase in the three historical periods, with 502 gullies in 1970, 771 gullies in 2011, and 1149 gullies in 2021. A total of 958 new gullies were newly initiated during the past 50 years. Among them, Excluding 311 gullies that hadwere excludeddisappeared after due to landfill human management by landfill, . a total of 958 new gullies were newly initiated during the past 50 years. The growth rate of gully number in Nenjiang in the north was higher than that of in Hailun in the middle, and Bayan in the south, indicating that the hot center of gully development are was moving northward. In the same latitude area, the number of gullies in the farmland with the large slope degree (3%) increased faster than that with the small slope degree (1% and 2%), and . this This difference was remained unchanged for over 50 years. In the period of the past 50 years, the The apparent area of gullies decreased during 1970 to 2011, and then increased during 2011 to 2021, show indicating a V-shaped trend due to human activity. However, there was the actual accelerated destroying speed of farmland by the growth of gullies accelerated in over the past 10 years, , with an average annual rate of 0.10% of the land area. of the study area and withThere was no difference in the three regions, which is was 10 times that of the average value of past 40 years earlier. The number and length of gullies in Nenjiang grow grew faster, because of at the younger stage of gully development in Nenjiang in this region in the north. The difference was found in the development stages of gully in the three latitude areas lead to. the There was noi nconsistencye between the number and length growth speed of the gully, compared with the area growth speed. The initial formation times years of gullies in the three latitude regions from the south to the north is were 1920s, 1940s, and 1950s, respectively, which is was consistent with the sequence of the black soil area opened up for farming. The development stages of gully in the typical black soil region is were divided into three stages: initiation of gully in the valley floor, formation of gully system with the slope gully emergence, and gully development in the multiple ways. Specifically,In the typical black soil region, Nenjiang has wasfinished the first stage and is in the second stage; , whereas, Hailun and Bayan have completed the first and second stages, and awere in the third stage in the typical black soil region. In the current third stage, several development ways were observed at the same time: the old gully growth, the secondary gully recurrence, the initiation of new gully, and the emergence of ephemeral gully. The results suggests thatTherefore, the developmental trend of gully in typical black soil area is was determined by as the competition between human control and promotion of gully development in the typical black soil area