Freeze-thaw (FT) events profoundly perturb the biochemical processes of soil and water in mid- and high-latitude regions, especially the riparian zones that are often recognized as the hotspots of soil-water interactions and thus one of the most sensitive ecosystems to future climate change. However, it remains largely unknown how the heterogeneously composed and progressively discharged meltwater affect the biochemical cycling of the neighbor soil. In this study, stream water from a valley in the Chinese Loess Plateau was frozen at -10 degrees C for 12 hours, and the meltwater (at +10 degrees C) progressively discharged at three stages (T1 similar to T3) was respectively added to rewet the soil collected from the same stream bed (Soil+T1 similar to Soil+T3). Our results show that: (1) Approximately 65% of the total dissolved organic carbon and 53% of the total NO3--N were preferentially discharged at the first stage T1, with enrichment ratios of 1.60 similar to 1.94. (2) The dissolved organic matter discharged at T1 was noticeably more biodegradable with significantly lower SUVA(254) but higher HIX, and also predominated with humic-like, dissolved microbial metabolite-like, and fulvic acid-like components. (3) After added to the soil, the meltwater discharged at T1 (e.g., Soil+T1) significantly accelerated the mineralization of soil organic carbon with 2.4 similar to 8.07-folded k factor after fitted into the first-order kinetics equation, triggering 125 similar to 152% more total CO2 emissions. Adding T1 also promoted significantly more accumulation of soil microbial biomass carbon after 15 days of incubation, especially on the FT soil. Overall, the preferential discharge of the nutrient-enriched meltwater with more biodegradable DOM components at the initial melting stage significantly promoted the microbial growth and respiratory activities in the recipient soil, and triggered sizable CO2 emission pulses. This reveals a common but long-ignored phenomenon in cold riparian zones, where progressive freeze-thaw can partition and thus shift the DOM compositions in stream water over melting time, and in turn profoundly perturb the biochemical cycles of the neighbor soil body.

Identifying the changes in terrestrial water storage is essential for a comprehensive understanding of the regional hydrological mass balance under global climate change. This study used a partial least square regression model to fill the observation gaps between GRACE and GRACE-FO and obtained a complete series of terrestrial water storage anomaly data from April 2002 to December 2020 from southeast China. We investigated the variations in terrestrial water storage anomalies in the region and the influencing factors. The study revealed that terrestrial water storage (TWS) anomalies have been increasing in the region, with an average increase of 0.33 cm/yr (p < 0.01). The intra-annual variation showed a positive anomaly from March to September and a negative anomaly in other months. Terrestrial water storage anomalies increased in most regions (especially in the central and northern parts), whereas they decreased in the southern parts. In terms of the components, the soil moisture storage (SMS) contributes 58.3 % and the surface water storage (SWS, especially reservoirs water storage) contributes 41.4 % to the TWS. The study also found that changes in the precipitation explain approximately 71.7 % of the terrestrial water storage variation, and reservoirs contributes to the remaining 28.3 %. These results are essential for understanding the changes in the hydrological cycle and developing strategies for water management in Southeast China.

Quantifying the impact of climate change on hydrologic features is essential for the scientific planning, management and sustainable use of water resources in Northwest China. Based on hydrometeorological data and glacier inventory data, the Spatial Processes in Hydrology (SPHY) model was used to simulate the changes of hydrologic processes in the Upper Shule River (USR) from 1971 to 2020, and variations of runoff and runoff components were quantitatively analyzed using the simulations and observations. The results showed that the glacier area has decreased by 21.8% with a reduction rate of 2.06 km(2)/a. Significant increasing trends in rainfall runoff, glacier runoff (GR) and baseflow indicate there has been a consistent increase in total runoff due to increasing rainfall and glacier melting. The baseflow has made the largest contribution to total runoff, followed by GR, rainfall runoff and snow runoff, with mean annual contributions of 38%, 28%, 18% and 16%, respectively. The annual contribution of glacier and snow runoff to the total runoff shows a decreasing trend with decreasing glacier area and increasing temperature. Any increase of total runoff in the future will depend on an increase of rainfall, which will exacerbate the impact of drought and flood disasters.

Study region: This study focuses on the upper reaches of Shule river (URSLH) and Heihe river (URHH) basins and Taolai river (URTLH) basin in Qilian Mountains.Study focus: The impact of the cryosphere changes on runoff components in basins with different cryosphere ratios.New hydrological insights for the region: Total runoff (TR) increased in URSLH and URHH and decreased in URTLH, snowmelt runoff (SR) decreased in each basin, glacier runoff (GR) increased in URSLH and URTLH but decreased in URHH during 1980-2015. In the future, GR will increase under SSP585 and slightly decrease under SSP126 in 2040-2060 in URSLH and decrease in URHH and URSLH. The peak time of SR will advance by a month in each basin. In the future, GR (The ratio of the coefficient of variation (cv) of TR to cv of non-glacial runoff) will decrease, indicating hydrological regulation of glaciers will be weakened in these basins. SR and Rs (The ratio of summer runoff to spring runoff) will show downward trends, the processes of TR increase will be smoother. Rr (The ratio of maximum to minimum monthly runoff) will show downward trends under SSPs. TR will become smoother in each basin. Furthermore, the change of each runoff components will make TR tends to be smoother in the future and reduce TR especially in summer.

Brown carbon (BrC) is a light-absorbing aerosol component that has a significant impact on atmospheric photochemistry and climate effects. Many studies on light absorbing characteristics of BrC (such as a fraction of water-soluble and/or water-insoluble) have been carried out in cities over the Guanzhong Basin, including radiative forcing, optical properties and sources. However, research on the Qinling Mountains is still lacking. Therefore, PM2.5 samples were collected at the northern piedmont of Qinling Mountains (QL) and Xi'an (XN) in the winter of 2020, and the optical properties and radiation effects of water extracts were analyzed and eval-uated. The mass absorption efficiency (MAE) of water-soluble organic carbon (WSOC) at 365 nm (MAE365) obtained in QL and XN were 0.18 +/- 0.03 m2 g-1 and 0.78 +/- 0.96 m2 g-1, respectively. In the ultraviolet range, the relative light absorption of WSOC relative to elemental carbon (EC) was 6.76% and 33.41% in QL and XN, respectively, and the simple forcing efficiency (SFE280-400) were 0.71 +/- 0.43 and 2.82 +/- 1.71 W g-1 in QL and XN. It may have important effects on the radiation balance of regional climate systems. The chromophores in WSOC of XN and QL are mainly composed of humic-like and protein-like substances, and humus-like substances play a dominant role in two sites (52.61% and 71.13%). Biomass combustion has a limited contribution to chromophore abundance in WSOC of QL, which is more affected by urban transmission. The fluorescence index revealed that the chromophores in WSOC had autogenous characteristics and that the organic matter was mostly newly generated. Furthermore, the molecular weight and aromatic degree in XN samples were higher than that in QL, indicating a greater capacity for light absorption. This work will be instrumental in assessing the inter-action and influence between the city and the northern piedmont of the Qinling Mountains and improve the capability of air pollution prevention and control of Guanzhong Basin.

Ice-wedge polygon troughs play an important role in controlling the hydrology of low-relief polygonal tundra regions. Lateral surface flow is confined to troughs only, but it is often neglected in model projections of permafrost thermal hydrology. Recent field and modeling studies have shown that, after rain events, increases in trough water levels are significantly more than the observed precipitation, highlighting the role of lateral surface flow in the polygonal tundra. Therefore, understanding how trough lateral surface flow can influence polygonal tundra thermal hydrology is important, especially under projected changes in temperatures and rainfall in the Arctic regions. Using an integrated cryohydrology model, this study presents plotscale end-of-century projections of ice-wedge polygon water budget components and active layer thickness with and without trough lateral surface flow under the Representative Concentration Pathway 8.5 scenario. Trough lateral surface flow is incorporated through a newly developed empirical model, evaluated against field measurements. The numerical scenario that includes trough lateral surface flow simulates discharge (outflow from a polygon) and recharge (rain-induced inflow to a polygon trough from upslope areas), while the scenario that does not include trough lateral surface flow ignores recharge. The results show considerable reduction (about 100-150%) in evapotranspiration and discharge in rainy years in the scenarios ignoring trough lateral surface flow, but less effect on soil water storage, in comparison with the scenario with trough lateral surface flow. In addition, the results demonstrate long-term changes (similar to 10-15 cm increase) in active layer thickness when trough lateral surface flow is modeled. This study highlights the importance of including lateral surface flow processes to better understand the long-term thermal and hydrological changes in low-relief polygonal tundra regions under a changing climate.

Vegetation is affected by hydrological cycle components that have altered under the influence of climate change. Therefore, it is necessary to investigate the impact of hydrological cycle components on regional vegetation growth, especially in alpine regions. In this study, we employed multiple satellite observations to comprehensively investigate the spatial heterogeneity of hydrological cycle components in the Yarlung Zangbo River (YZR) basin for the period 1982-2014 and to determine the underlying mechanisms driving regional vegetation growth. Results showed that the normalized difference vegetation index (NDVI) values during May-October were high, and the NDVI values increased from the upper reaches of the YZR to its lower reaches, reflecting the enhancement of vegetation growth. Annual precipitation, precipitation-actual evapotranspiration (AET), and snow water equivalent (SWE) all affect terrestrial water storage in the YZR basin through changes in soil moisture (SM), i.e., SM is the intermediate variable. Seasonal variability of vegetation is controlled mainly by precipitation, temperature, AET, SM anomaly, and SWE. Groundwater storage anomalies (GWA) and terrestrial water storage anomalies (TWSA) were not reliable indicators of vegetation growth in the YZR basin and the midstream and downstream regions. The effects of GWA and TWSA on vegetation occurred in the upstream region.

The glacier river is highly sensitive to the temperature and precipitation change in the alpine regions. However, to what extent of this sensitivity is still not clear. In this work, a procedure to quantify the impact of temperature and precipitation on water runoff components is proposed with a benchmark study at a typical temperate glacier catchment of Mingyong in the southeastern Tibetan Plateau (SETP). Firstly, we use Bayesian Monte Carlo Mixing Model to calculate contributions of different recharging sources to runoff from 213 water samples within a whole hydrological year (from August 2017 to July 2018). Hydrograph separation results show that the meltwater occupied the highest proportion in runoff from June to September (up to 58.4%) and the contribution of groundwater to runoff reached the maximum in January. Secondly, by establishing the relationships between temperature, precipitation and fractions of runoff components, we find that temperature change contributes about 78% to affecting the runoff components in Mingyong catchment at the intra-annual scale. Meanwhile, precipitation change occupies approximately 22% in influencing contributions of different endmembers to stream mainly by accelerating the melting process of glacier and accumulated snow as well as recharging the river directly. Finally, a conceptual model is developed to show the influence of temperature and precipitation on the runoff components in Mingyong catchment. The findings can not only provide essential evidence on gaining more insights into the mechanism of glacier river flow variation but also benefit for the strategy making for water resources management in alpine regions.

We estimated the current (base years) and future (2021-2100) direct radiative forcing ( DRF) of four aerosol components (water-soluble, insoluble, black carbon (BC), and sea-salt) at urban (Yeonsan (Busan) and Gwangjin (Seoul)) and background sites (Aewol and Gosan (Jeju Island)), based on a modeling approach. The analysis for base years was conducted using PM2.5 samples measured at two urban and two background sites (Yeonsan and Gwangjin: 2016, Aewol and Gosan: 2014). The future DRFs were estimated according to changes in relative humidity (RH) of RCP8.5 climate change scenario at the same sites during four different periods (PI: 2021 similar to 2040, PII: 2041 similar to 2060, PIII: 2061 similar to 2080, and PIV: 2081 similar to 2100). In addition, we compared the differences between the DRFs of future (PI similar to PIV) and base years (2016 and 2014). Overall, the water-soluble component was predominant over all other components in terms of the concentrations, optical parameters (e.g., AOD), and DRFs, regardless of sites. For the base years, the monthly patterns of total DRFs for all components and the DRFs for the water-soluble component varied with sites, and months of their highest and lowest DRFs were different depending on sites. This might be due to the combined effect of the monthly patterns of the concentrations and RHs for each site. For the differences between the DRFs of future and base years, the highest future DRFs at Yeonsan and Aewol ranged from -59 to -63 W/m(2) increasing -20 (July in PII) to -28 W/m(2) (August in PIII) compared to the base years and from -73 to -74 W/m(2) increasing -31 (July in PII) to -41 W/m(2) (September in PIV), respectively. These DRFs at Gwangjin and Gosan ranged from -79 to -84 W/m(2) increasing -29 (June in PII and PIII) to -34 W/m(2) (June in PI) and from -58 to -92 W/m(2) increasing -14 (July in PII) to -26 W/m(2) (May in PI), respectively. The high heating rates at Yeonsan (up to 4.4 K/day in November) and Aewol (up to 3.7 K/day in February) of BC component might be caused by its strong radiative absorption.

Carbonaceous particles play an important role in climate change, and an increase in their emission and deposition causes glacier melting in the Himalayas and the Tibetan Plateau (HTP). This implies that studying their basic characteristics is crucial for a better understanding of the climate forcing observed in this area. Thus, we investigated characteristics of carbonaceous particles at a typical remote site of southeastern HTP. Organic carbon and elemental carbon concentrations at this study site were 1.86 +/- 0.84 and 0.18 +/- 0.09 mu g m(-3), respectively, which are much lower than those reported for other frequently monitored stations in the same region. Thus, these values reflect the background characteristics of the study site. Additionally, the absorption coefficient per mass (alpha/rho) of water-soluble organic carbon (WSOC) at 365 nm was 0.60 +/- 0.19 m(2) g(-1), with the highest and lowest values corresponding to the winter and monsoon seasons, respectively. Multi-dimensional fluorescence analysis showed that the WSOC consisted of approximately 37% and 63% protein and humic-like components, respectively, and the latter was identified as the component that primarily determined the light absorption ability of the WSOC, which also showed a significant relationship with some major ions, including SO42-, K+, and Ca2+, indicating that combustion activities as well as mineral dust were two important contributors to WSOC at the study site. (C) 2020 Elsevier Ltd. All rights reserved.