There is 78 % permafrost and seasonal frozen soil in the Yangtze River's Source Region (SRYR), which is situated in the middle of the Qinghai-Xizang Plateau. Three distinct scenarios were developed in the Soil and Water Assessment Tool (SWAT) to model the effects of land cover change (LCC) on various water balance components. Discharge and percolation of groundwater have decreased by mid-December. This demonstrates the seasonal contributions of subsurface water, which diminish when soil freezes. During winter, when surface water inputs are low, groundwater storage becomes even more critical to ensure water supply due to this periodic trend. An impermeable layer underneath the active layer thickness decreases GWQ and PERC in LCC + permafrost scenario. The water transport and storage phase reached a critical point in August when precipitation, permafrost thawing, and snowmelt caused LATQ to surge. To prevent waterlogging and save water for dry periods, it is necessary to control this peak flow phase. Hydrological processes, permafrost dynamics, and land cover changes in the SRYR are difficult, according to the data. These interactions enhance water circulation throughout the year, recharge of groundwater supplies, surface runoff, and lateral flow. For the region's water resource management to be effective in sustaining ecohydrology, ensuring appropriate water storage, and alleviating freshwater scarcity, these dynamics must be considered.

Sources and implications of black carbon (BC) and mineral dust (MD) on two glaciers on the central Tibetan Plateau were estimated based on in situ measurements and modeling. The results indicated that BC and MD accounted for 11 +/- 1% and 4 +/- 0% of the albedo reduction relative to clean snow, while the radiative forcing varied between 11 and 196 and 1-89 W m(-2), respectively. Assessment of BC and MD contributions to the glacier melt can reach up 88 to 434 and 35 to 187 mm w.e., respectively, contributing 9-23 and 4-10% of the total glacier melt. A footprint analysis indicated that BC and MD deposited on the glaciers originated mainly from the Middle East, Central Asia, North China and South Asia during the study period. Moreover, a potentially large fraction of BC may have originated from local and regional fossil fuel combustion. This study suggests that BC and MD will enhance glacier melt and provides a scientific basis for regional mitigation efforts.

The transboundary mercury (Hg) pollution has caused adverse effects on fragile ecosystems of the Tibetan Plateau (TP). Yet, knowledge of transport paths and source regions of atmospheric Hg on the inland TP remains poor. Continuous measurements of atmospheric total gaseous mercury (TGM) were conducted in the central TP (Tanggula station, 5100 m a.s.l., June -October). Atmospheric TGM level at Tanggula station (1.90 +/- 0.30 ng m -3 ) was higher than the background level in the Northern Hemisphere. The identified high -potential source regions of atmospheric TGM were primarily located in the northern South Asia region. TGM concentrations were lower during the Indian summer monsoon (ISM) -dominant period (1.81 +/- 0.25 ng m -3 ) than those of the westerly -receding period (2.18 +/- 0.40 ng m -3 ) and westerly -intensifying period (1.91 +/- 0.26 ng m -3 ), contrary to the seasonal pattern in southern TP. The distinct TGM minima during the ISM -dominant period indicated lesser importance of ISM -transported Hg to Tanggula station located in the northern boundary of ISM intrusion, compared to stations in proximity to South and Southeast Asia source regions. Instead, from the ISM -dominant period to the westerly -intensifying period, TGM concentrations showed an increasing trend as westerlies intensified, indicating the key role of westerlies in transboundary transport of atmospheric Hg to the inland TP.

Permafrost and its spatiotemporal variation considerably influence the surface and sub-surface hydrological processes, biogeochemical cycles, fauna and flora growth and cold region engineering projects in the Three-River Source Region (TRSR), Qinghai-Tibet Plateau. However, the dynamics of permafrost over a relatively long term duration (e.g. >100 years) in the TRSR is not well quantified. Thus, the spatial and temporal variations of the temperature at the top of the perennially frozen/unfrozen ground (TTOP), active layer thickness (ALT) in permafrost regions and the maximum depth of frost penetration (MDFP) in the seasonally frozen ground of the TRSR during 1901-2020 were simulated using the TTOP model and Stefan equation driven by the widely used reanalysis Climatic Research Unit 4.05 dataset. Results revealed that the permafrost in the TRSR over the past 120 years did not degrade monotonically but experienced considerable fluctuations in area with the decadal oscillations of climate warming and cooling: shrinking from 263.9 x 103 km2 in the 1900s to 233.3 x 103 km2 in the 1930s, expanding from 232.3 x 103 km2 in the 1940s to 260.9 x 103 km2 in the 1970s and shrinking again from 254.1 x 103 km2 in the 1980s to 228.9 x 103 km2 in the 2010s. The regional average TTOP increased from -1.34 & PLUSMN; 2.74 & DEG;C in the 1910s to -0.48 & PLUSMN; 2.69 & DEG;C in the 2010s, demonstrating the most noticeable change for the extremely stable permafrost (TTOP 3.0 m by 12% from 1901 to 2020. Notably, minor changes were observed for the regional average MDFP, probably due to the increase in the area proportion of MDFP 3.5 m (owing to the transformation of permafrost to seasonally frozen ground) by 7.39% and 4.77%, respectively. These findings can facilitate an in-depth understanding of permafrost dynamics and thus provide a scientific reference for eco-environment protection and sustainable development under climate change in the TRSR

Assessing the characteristics of runoff changes and quantifying the contribution of influencing factors to runoff changes are crucial for water resources management and sustainable development in the source region of the Yellow River (SRYR). The intra-annual distribution of runoff depicted a double-peak effect. The first runoff peak in July was primarily influenced by precipitation, which did not completely flow after falling to the ground. However, some water was stored in the active layer of permafrost and released in September resulting in the second runoff peak. The contributions of precipitation and temperature to the runoff changes were 74.2% and 25.8%, respectively. The runoff peaks advanced by 15 and 6 days for the first and second peaks, respectively, owing to the influence of the cryosphere change. Principal component analysis revealed that the contributions of climate change and human activity to runoff fluctuations were 72.9% and 27.1%, respectively, during 1961-2018, indicating that hydrological processes were mainly influenced by climate change in the SRYR. The combined effect of climate change created a warm and dry trend after 1990, indicating a spatial distribution of wetness in the northwest and aridity in the southeast of the SRYR.

As an important water source and ecological barrier in the Yellow River Basin, the source region of the Yellow River (above the Huangheyan Hydrologic Station) presents a remarkable permafrost degradation trend due to climate change. Therefore, scientific understanding the effects of permafrost degradation on runoff variations is of great significance for the water resource and ecological protection in the Yellow River Basin. In this paper, we studied the mechanism and extent of the effect of degrading permafrost on surface flow in the source region of the Yellow River based on the monitoring data of temperature and moisture content of permafrost in 2013-2019 and the runoff data in 1960-2019. The following results have been found. From 2013 to 2019, the geotemperature of the monitoring sections at depths of 0-2.4 m increased by 0.16 degrees C/a on average. With an increase in the thawing depth of the permafrost, the underground water storage space also increased, and the depth of water level above the frozen layer at the monitoring points decreased from above 1.2 m to 1.2-2 m. 64.7% of the average multiyear groundwater was recharged by runoff, in which meltwater from the permafrost accounted for 10.3%. Compared to 1960-1965, the runoff depth in the surface thawing period (from May to October) and the freezing period (from November to April) decreased by 1.5 mm and 1.2 mm, respectively during 1992-1997, accounting for 4.2% and 3.4% of the average annual runoff depth, respectively. Most specifically, the decrease in the runoff depth was primarily reflected in the decreased runoff from August to December. The permafrost degradation affects the runoff within a year by changing the runoff generation, concentration characteristics and the melt water quantity from permafrost, decreasing the runoff at the later stage of the permafrost thawing. However, the permafrost degradation has limited impacts on annual runoff and does not dominate the runoff changes in the source region of the Yellow River in the longterm.

Global warming has led to permafrost degradation worldwide. The Qinghai-Tibet Plateau (QTP) hosts most of the world's alpine permafrost, yet its impending changes remain largely unclear, thereby affecting regional hydrological and ecological processes and the global carbon budget. By employing a land surface model adapted to simulate frozen ground, and using state-of-the-art multi-model and multi-scenario data from the Coupled Model Intercomparison Project Phase 6, changes in permafrost distribution and its thermal regimes on the QTP are systematically predicted under various shared socioeconomic pathways (SSPs). Projections for SSP2-4.5, SSP3-7.0, and SSP5-8.5 show that most of the continuous permafrost region of the QTP will persist through 2050. Much of the permafrost is likely to degrade in the late 21st century, with projected area losses of 44 +/- 4%, 59 +/- 5%, and 71 +/- 7%, respectively, by 2100. In particular, the Three Rivers Source region in the central eastern part of the QTP is a key area of permafrost degradation, where permafrost is most vulnerable and degradation occurs earliest. The mean annual ground temperature of QTP permafrost will increase by 0.8 +/- 0.2 degrees C, 2.0 +/- 0.3 degrees C, and 2.6 +/- 0.3 degrees C under SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively, and the active layer thickness will increase by 0.7 +/- 0.1 m, 1.5 +/- 0.3 m, and 3.0 +/- 1.0 m, respectively. The surviving permafrost under SSP3-7.0 and SSP5-8.5 will be thermally unstable, which is a clear warning sign of complete disappearance. The analysis of permafrost sensitivity to climate change signifies that alpine permafrost on the QTP has low resilience to climate change, in contrast to permafrost in pan-Artic high latitudes.

The source region of the Yangtze River (SRYR), located on the eastern Tibetan Plateau, is an essential part of the Asian Water Tower and plays an important role in the downstream water resources. Significant changes in frozen ground caused by increases in air temperature have been widely reported in the past several decades, which has greatly affected regional runoff. This study evaluated the spatiotemporal variations in frozen ground and hydrological components by utilizing a geomorphology-based eco-hydrological model (GBEHM) and investigated the reasons for runoff changes based on the Budyko framework. The results showed that the area with an elevation range of 4700-4800 m located in the permafrost region was the main source area of runoff generation from 1981 to 2015. Compared with the permafrost region, the seasonally frozen ground (SFG) region had a larger ratio of annual evapotranspiration to annual precipitation, although the aridity indices in the two regions were very similar. From 1981 to 2015, the mean value of the maximum frozen depth of SFG (MFDSFG) decreased by 12.3 cm/10 a and the mean value of the active layer thickness (ALT) of permafrost increased by 4.2 cm/10 a. The annual runoff in the SFG region decreased, while that in the permafrost region increased. Runoff change was more sensitive to precipitation change in the higher altitude regions that were mainly covered by permafrost than in the lower altitude regions that were mainly covered by the SFG, while the evapotranspiration change in the transition zone was more sensitive to climate change. An abrupt change in the annual runoff time series was detected in 1989, 2004, and 2004 in the SFG region, the permafrost region and the entire SRYR, respectively, and the annual runoff change from period 1 (1981 to change point) to period 2 (change point + 1 to 2015) were - 25.7 mm, 33.8 mm and 25.8 mm respectively. Frozen ground degradation contributed changes of -15.0 mm, - 8.8 mm and -11.6 mm to the annual runoff in the SFG region, the permafrost region and the entire SRYR, respectively. This result implied that frozen ground degradation had a negative impact on regional runoff in the SRYR. These findings deepen our understanding of frozen ground and its hydrological changes and are helpful for water resource management in the SRYR.

Frozen ground degradation under a warming climate profoundly influences the growth of alpine vegetation in the source region of the Qinghai-Tibet Plateau. This study investigated spatiotemporal variations in the frozen ground distribution, the active layer thickness (ALT) of permafrost (PF) soil and the soil freeze depth (SFD) in seasonally frozen soil from 1980 to 2018 using the temperature at the top of permafrost (TTOP) model and Stefan equation. We compared the effects of these variations on vegetation growth among different frozen ground types and vegetation types in the source region of the Yellow River (SRYR). The results showed that approximately half of the PF area (20.37% of the SRYR) was projected to degrade into seasonally frozen ground (SFG) during the past four decades; furthermore, the areal average ALT increased by 3.47 cm/yr, and the areal average SFD decreased by 0.93 cm/yr from 1980 to 2018. Accordingly, the growing season Normalized Difference Vegetation Index (NDVI) presented an increasing trend of 0.002/10yr, and the increase rate and proportion of areas with NDVI increase were largest in the transition zone where PF degraded to SFG (the PF to SFG zone). A correlation analysis indicated that variations in ALT and SFD in the SRYR were significantly correlated with increases of NDVI in the growing season. However, a rapid decrease in SFD (< -1.4 cm/10yr) could have reduced the soil moisture and, thus, decreased the NDVI. The NDVI for most vegetation types exhibited a significant positive correlation with ALT and a negative correlation with SFD. However, the steppe NDVI exhibited a significant negative correlation with the SFD in the PF to SFG zone but a positive correlation in the SFG zone, which was mainly limited by water condition because of different change rates of the SFD.

Sources and implications of black carbon (BC) and mineral dust (MD) on two glaciers on the central Tibetan Plateau were estimated based on in situ measurements and modeling. The results indicated that BC and MD accounted for 11 +/- 1% and 4 +/- 0% of the albedo reduction relative to clean snow, while the radiative forcing varied between 11 and 196 and 1-89 W m(-2), respectively. Assessment of BC and MD contributions to the glacier melt can reach up 88 to 434 and 35 to 187 mm w.e., respectively, contributing 9-23 and 4-10% of the total glacier melt. A footprint analysis indicated that BC and MD deposited on the glaciers originated mainly from the Middle East, Central Asia, North China and South Asia during the study period. Moreover, a potentially large fraction of BC may have originated from local and regional fossil fuel combustion. This study suggests that BC and MD will enhance glacier melt and provides a scientific basis for regional mitigation efforts.