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Alluvial fans have been proven to have great utilisation potential in QTP, but to what extent they are suitable for agricultural development is unknown. Therefore, using the alluvial fan in the Lhasa River Basin (LRB) as a case study, this paper established an evaluation system of land suitability for agriculture (LSA). Principal component analysis (PCA) and the exhaustive method (EM) were used to define the minimum dataset (MDS) and then the LSA of the alluvial fan in the LRB was evaluated using a comprehensive index of LSA. Two scientific approaches were implemented to improve the LSA using a scenario simulation. The results showed that the MDS assessed by the EA was more representative compared to the PCA. Alluvial fans with suitable grades are mainly distributed in the Lhasa River's middle and lower reaches. Developing facility agriculture and repairing roads accessing the alluvial fans are effective approaches to improve the LSA, which can increase the suitable-grade area from 58.62% to 97.82% and 63.85%, respectively. Therefore, most alluvial fans in the LRB are suitable for developing agriculture, and under the influence of human activities, there will be more alluvial fans suitable for developing agriculture. Our research provides scientific methods for the sustainable development of land in alpine regions. [ABSTRACT FROM AUTHOR]

Alluvial fans are an important land resource with agricultural potential in Qinghai–Tibet Plateau. The spatiotemporal variation in land use/cover is an important indicator to understand the value of alluvial fans and protect and make scientific use of such fans. In this study, the spatiotemporal characteristics of land use/cover are determined by analysing the land use/cover changes of alluvial fans in the Lhasa River Basin (LRB) at different times, counties/districts, altitudes, and gradients. Results show that the area of cultivated land and the artificial land provided by alluvial fans for LRB has continuously increased. In 2000, 2010, and 2020, 17.72%, 21.84%, and 24.17% of cultivated land and 7.89%, 7.51%, and 25.24% of artificial land in LRB were provided by alluvial fans, respectively. At all altitudes and slopes, cultivated land and artificial land are increasing but the increasing part is basically due to the massive loss of grassland. The spatiotemporal changes in all land use/cover types of alluvial fans were dominated by human activities, although they were also influenced by natural factors to some degree. [ABSTRACT FROM AUTHOR]

In the Lower Lhasa River basin of the Tibetan Plateau, gully erosion poses a threat to alluvial fans (AF), which are the main available land resource for agriculture. Runoff from the whole contributing catchment is concentrated in AF, which makes influencing factors of AF gully erosion more complex than it is for hillslopes. There is a lack of quantitative research about the influencing factors and mechanisms of AF gully erosion. The main objectives of this study were to: (1) quantify gully erosion on AF; and (2) identify the controlling factors of gully erosion on AF. The gullies of 12 AF were investigated by unmanned aerial vehicle (UAV). To help understand better the gully erosion on AF, nine morphological parameters were measured, four gully quantitative characteristics were calculated, and 16 factors affecting the gully erosion on AF were analyzed. The gully width–depth ratio of over 20 on the studied AF is larger than that usually seen in other regions. The mean value of gully amount density (GAD), gully density (GD), the degree of gully dissection (GDD), and gully volume modulus (GVM) were 26.51 km−2, 4.93 km·km−2, 7.16%, and 1.28 × 10−4 km3·km−2, respectively. Linear correlations showed a significant (p < 0.05) relationship between the gully quantitative characteristics of AF and the catchment gully density. So, catchment gully density may indirectly affect gully erosion on AF by influencing hydrological connectivity and then changing generation and confluence processes of runoff in catchment. Therefore, gully erosion on AF can be mitigated by shifting hydrology pathway on AF and reducing hydrological connectivity in contributing catchment. [ABSTRACT FROM AUTHOR]

Vegetation plays an important role in gully headcut erosion in China's Loess Plateau, but little is known about the effects of root density on gully headcut erosion. This study attempted to investigate the effects of grass root density on gully headcut erosion and morphological development of the gully head using plots with different grass root densities (with bare land as the control). The experiment was performed on plots with different grass root densities, and the rainfall intensity and inflow discharge increased throughout the experiment. The results showed that headcut migration in bare land was mainly activated by upstream flow incision, headwall erosion, and plunge pool erosion, whereas headcut migration in grassland was driven by soil‐root matrix collapse at the headcut, headwall erosion, and plunge pool erosion. The soil loss rate (SLR), gully headcut retreat distance (GRD), gully area (GA), and upstream soil loss volume (SLVU) in grassland plots with different root densities were 45.64–68.45%, 66.97–85.38%, 69.26–78.18%, and 67.89–87.02% less than those in the bare land plots, respectively. However, as root density increased, the gully depth in the grassland plots increased from 19% to 59%, and the proportion of gully head soil loss volume (SLVGH) to the total soil loss volume increased from 63.37% to 88.37%. The SLR, GRD, GA, and SLVGH showed decreasing trends as the root density increased, as described by a Hill curve. Moreover, roots with diameters of 0–0.5 mm had greater effects on soil loss and morphological evolution than roots with larger diameters. Our results provide a reference for the reasonable selection of grass root density for controlling gully headcut erosion in China's Loess Plateau. [ABSTRACT FROM AUTHOR]

• Alluvial fans' soil quality in Lhasa River Basin was evaluated. • Soil quality index (SQI) was applied to alluvial fan and river terrace farmland. • No significant difference in physicochemical parameters was observed between two landforms. • Soil quality of alluvial fans was similar to river terrace farmland. Determining the soil quality of alluvial fans and its influencing factors is essential for understanding, utilizing, and protecting alluvial fans. In this study, a soil quality index (SQI) was constructed, and the soil of river terrace farmland was used as a control to evaluate the soil quality of alluvial fans in the Lhasa River Basin of the Qinghai-Tibet Plateau. Meanwhile, the influencing factors of soil quality of the alluvial fan were studied using correlation analysis. The results demonstrated that: 1) There is no significant difference in physicochemical indicators between the soil of the alluvial fan and river terrace farmland, namely the total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, soil organic matter, pH, electrical conductivity, and soil erodibility; however, the coefficient of variation of each physicochemical indicator of the alluvial fan is greater than that of river terrace farmland. 2) The mean SQI value of alluvial fans and river terrace farmlands are 0.37 and 0.38, respectively. There is no significant difference between the values, demonstrating that the soil quality of alluvial fans is not lower than that of river terrace farmland. 3) The soil quality of alluvial fans has a highly significant positive correlation with vegetation coverage, land use, annual precipitation, altitude, and geomorphic divisions; a significant positive correlation with geomorphic location; and a highly significant negative correlation with annual temperature. Therefore, from the perspective of soil quality, the alluvial fan in the Lhasa River Basin can be used as a reserve arable land resource. [ABSTRACT FROM AUTHOR]