The scientific community has widely reported the impacts of climate change on the Central Himalaya. To qualify and quantify these effects, long-term land surface temperature observations in both the daytime and nighttime, acquired by the Moderate Resolution Imaging Spectroradiometer from 2000 to 2017, were used in this study to investigate the spatiotemporal variations and their changing mechanism. Two periodic parameters, the mean annual surface temperature (MAST) and the annual maximum temperature (MAXT), were derived based on an annual temperature cycle model to reduce the influences from the cloud cover and were used to analyze their trend during the period. The general thermal environment represented by the average MAST indicated a significant spatial distribution pattern along with the elevation gradient. Behind the clear differences in the daytime and nighttime temperatures at different physiographical regions, the trend test conducted with the Mann-Kendall (MK) method showed that most of the areas with significant changes showed an increasing trend, and the nighttime temperatures exhibited a more significant increasing trend than the daytime temperatures, for both the MAST and MAXT, according to the changing areas. The nighttime changing areas were more widely distributed (more than 28%) than the daytime changing areas (around 10%). The average change rates of the MAST and MAXT in the daytime are 0.102 °C/yr and 0.190 °C/yr, and they are generally faster than those in the nighttime (0.048 °C/yr and 0.091 °C/yr, respectively). The driving force analysis suggested that urban expansion, shifts in the courses of lowland rivers, and the retreat of both the snow and glacier cover presented strong effects on the local thermal environment, in addition to the climatic warming effect. Moreover, the strong topographic gradient greatly influenced the change rate and evidenced a significant elevation-dependent warming effect, especially for the nighttime LST. Generally, this study suggested that the nighttime temperature was more sensitive to climate change than the daytime temperature, and this general warming trend clearly observed in the central Himalayan region could have important influences on local geophysical, hydrological, and ecological processes.

Gully initiation has been a subject of much discussion in the field of gully erosion. Gully initiation could be examined by the S–A relationship (S = aA ^{− b} ) between the critical slope of the gully head (S) and the upstream drainage area (A). Gully erosion plays an important role in sediment yield and land degradation in the Dry-hot Valley region of Southwest China; however, little research has focused on gully development in this region. This study investigated gully morphology and the critical topographic threshold of permanent gullies in Yuanmou Dry-hot Valley. Data for 36 gully heads were derived from the gully digital elevation model created by high-precision real-time kinematic GPS (RTK GPS). A significant relationship between gully length and volume (r ² = 0.77, p < 0.01) was found to exist, indicating that gully length can be used to estimate the gully erosion rate. Additionally, as vegetation coverage inside the gully increases, the gully morphology tends to be stable. The S–A relationship was S = 0.5195A ^−.0899, while AS ² values ranged between 4.2 and 758.5 m². The low value of constant b (0.0899) indicates that collapse of the gully wall is the dominant process of gully erosion in Yuanmou Dry-hot Valley.

Headcut erosion has been recognized as one of the main processes involved in gully development in the dry-hot valley region of southwest China. To examine the effect of initial step height on headcut erosion processes, three headcuts were constructed ranging in height from 0.75 to 1.25 m on an active bank gully head, and a series of scouring experiments were conducted under a flow discharge of 120 L min⁻¹. The morphological evolutions of the plunge pools and soil loss volume were estimated by three-dimensional photo-reconstruction methods (3D-PR). As the step height increased, the experimental results showed that: (1) the transformed potential energy and shear stress would increase by approximately 4.89 J s⁻¹ and 26.4 Pa on average when the step height increased 0.25 m; (2) the mean depth and width of the plunge pool exhibited obvious growth, and the morphology of the cross-section developed from approximately V-shaped to U-shaped; and (3) soil loss volume increased logarithmically, with total soil loss volumes of 0.076, 0.105 and 0.116 m³, respectively. Although the significant effects of the initial step height on headcut erosion were verified, further quantitative studies are required to quantify the mechanism of headcut erosion, especially for plunge pool erosion.