Unpaved road erosion after heavy storms in mountain areas of northern China

More frequent extreme rainfall events associated with global climate change cause greater challenges for soil conservation.Severe erosion occurs on many unpaved roads since these structures create important water flow paths during heavy storms.The present research aimed to investigate the intensity and influencing factors of unpaved road erosion under varied land use and management conditions(sloping cropland,terraced cropland,forest&grass).The erosion occurred in the watersheds contributing runoff water to roads after the greatest rainfall event recorded in the mountain area of northern China caused by Typhon Lekima.The research was conducted in an agricultural-forest-dominated watershed based on field investigation and UAV-based image analysis.A road erosion level classification standard was given according to the occurrence of rills,ephemeral gullies,and gullies.Significant erosion happened on 67% of the unpaved roads;42% of them suffered moderate to severe erosion in which ephemeral gullies or gullies developed.The average erosion amount from these roads was 2280.75 t ha-1 and was significantly influenced by the watershed land use type and management.The dominant factor governing unpaved road erosion associated with terraced cropland was vegetation coverage on roads.Drainage area was the most important factor for road erosion in sloping cropland and forest&grass land,and road gradient was also a critical factor.Terraces,and forest&grass in drainage areas significantly reduced unpaved road erosion by 85%and,47%,respectively,compared to sloping cropland.More integrated measures should be used to prevent unpaved road erosion.The results of this research can be applied to road protection against erosion in heavy storms.

A Mesoscale Analysis of Heavy Rain Caused by Frontal and Topographical Heterogeneities on Taiwan Island

The prevailing mesoscale model MM5 (V3) is used to simulate a heavy rain case caused by interac- tion between a move-in front and topographical heterogeneities on Taiwan Island. It is found that both thermodynamic and dynamic ?elds along the front are heterogeneous in time and space. The heterogene- ity becomes more signi?cant as the e?ect of topography is added on. The heterogeneous distribution of physical variables along the front is the main reason for the heterogeneous frontal rain band; the optimum cooperation of the low level and upper level jet is another reason for the development of the rain band. Topography can strengthen the rainfall and causes extremely heavy rain cells. Updraft induced by topog- raphy extends to a rather low level, while the uplifted air by frontal circulation can reach to higher levels. The quasi-steady topographic circulation overlaps the frontal circulation when the front moves over Taiwan Island; the advantageous cooperation of various mesoscale conditions causes the large upward velocity on the windward side of the island.

Gully internal erosion triggered by a prolonged heavy rainfall event in the tableland region of China's Loess Plateau

Gully erosion is a severe form of soil erosion,but gully internal erosion processes are poorly understood,especially at the event scale.To investigate gully internal erosion intensity and understand the related gully development mechanism in an agricultural environment with gully head stabilization and vege-tation restoration efforts,two successive field investigations were carried out just before and after a prolonged rainfall event in 2021 in the tableland region of China's Loess Plateau.Thirteen gullies were investigated and all experienced gully internal erosion,while most gully boundaries were stable during the heavy rainfall event based on the comparison of the UAV digital orthograph maps(DOMs acquired with Unmanned Aerial Vehicle)before and after the rainfall event.The proportion of gully internal erosion area to gully internal area of the 13 investigated gullies ranged from 3 to 55%,with average areal erosion proportion of the gully sidewall and gully bed of 21%and 36%,respectively.The erosion area of subdrainage units(SDUs)on the gully sidewall was positively correlated to the SDU area,average SDU slope gradient and vegetation type,while the erosion area on the gully bed was positively correlated to the gully area,gully depth and gully bed slope gradient.Gully internal erosion was not significantly correlated with gully drainage area because the connectivity between the upslope and gully areas was interrupted and the effective drainage area of the gully was obviously reduced by soil erosion conser-vation measures,including terraces on the upslope drainage area,shrub belts,and water barriers.Thus,gully internal erosion is still active under the heavy rainfall storm against the background of the'Grain for Green'and'Gully Stabilization and Tableland Protection'programs,and integrated measures for preventing both gully expansion and gully internal erosion must be further enhanced in the context of climate change.