Study region: The Qinghai Lake basin, including China's largest saltwater lake, is located on the Qinghai-Tibetan Plateau (QTP). Study focus: This study focuses on the hydrological changes between the past (1971-2010) and future period (2021-2060) employing the distributed hydrological model in the Qinghai Lake basin. Lake evaporation, lake precipitation, and water level changes were estimated using the simulations driven by corrected GCM data. The impacts of various factors on the lake water levels were meticulously quantified. New hydrological insights: Relative to the historical period, air temperatures are projected to rise by 1.72 degrees C under SSP2-4.5 and by 2.21 degrees C under SSP5-8.5 scenarios, and the future annual precipitation will rise by 34.7 mm in SSP2-4.5 and 44.1 mm in SSP5-8.5 in the next four decades. The ground temperature is projected to show an evident rise in the future period, which thickens the active layer and reduces the frozen depth. The runoff into the lake is a pivotal determinant of future water level changes, especially the runoff from the permafrost degradation region and permafrost region dominates the future water level changes. There will be a continuous rapid increase of water level under SSP5-8.5, while the water level rising will slow down after 2045 in the SSP2-4.5 scenario. This study provides an enhanced comprehension of the climate change impact on QTP lakes.

Freezing and thawing profoundly affect soil carbon cycling. Under the influence of climate change, rising temperatures and glacier shrinkage in arid regions have increased the spring river supply to lakes. However, intense evaporation in summer and seasonal fluctuations in lake water levels alter the magnitude and direction of carbon emissions. Yet, the mechanisms of temperature and groundwater level factors on arid zone lake wetlands remain unclear. This study, through field monitoring, found that during soil freezing periods, Phragmites reduced emissions by 95.21% and increased emissions by 3.91% during thawing periods. Tamarix Chinensis and bare land exhibited a decrease in carbon uptake of 42.77% and 85.25% during soil freezing periods, and a decrease in carbon uptake of 41.98% and 2.17% during thawing periods. By constructing a freeze-thaw simulation device, we simulated CO2 emissions characteristics under different water level conditions during freeze-thaw processes, including water injection at 10 cm, 20 cm, 30 cm, 40 cm (corresponding to water levels 40 cm, 30 cm, 20 cm, 10 cm below the soil surface), as well as scenarios of anhydrous and flooding periods. The results showed that under freeze-thaw conditions, Phragmites exhibited the strongest carbon uptake when water was injected at 20 cm, transitioning from emissions during the anhydrous period to carbon uptake. Tamarix Chinensis exhibited the strongest carbon uptake during freeze-thaw cycles when water was injected at 10 cm, showing a 93.69% increase compared to the anhydrous period. Meanwhile, the bare land exhibited the strongest carbon uptake during freeze-thaw cycles in the no water period. Lower temperatures and higher water levels favor increased carbon uptake in lake wetlands. This study identifies optimal water levels for carbon uptake in lake wetlands during freeze-thaw, and the important role of water level and temperature conditions on carbon emissions, providing valuable insights for assessing the carbon feedback mechanisms in lake wetlands under future climate change.

Lakes in permafrost regions are highly sensitive to changes in air temperature, snowmelt, and soil frost. In particular, the Qinghai-Tibetan Plateau (QTP) is one of the most sensitive regions in the world influenced by global climate change. In this study, we use retracked Enivsat radar altimeter measurements to generate water level change time series over Lake Qinghai and Lake Ngoring in the northeastern QTP and examine their relationships with precipitation and temperature changes. The response of water levels in Lake Qinghai and Lake Ngoring is positive with regards to precipitation amount. There is a negative relationship between water level and temperature change. These findings further the idea that the arid and high-elevation lakes in the northeastern QTP are highly sensitive to climate variations. Water level increases in Lake Qinghai in winter may indicate inputs of subsurface water associated with freeze-thaw cycles in the seasonally frozen ground and the active layer.