Guohua Liu

Water conservation is a key regulating service provided by terrestrial ecosystems, and its variation directly affects regional water security and ecosystem health. Existing studies of water conservation have focused largely on quantitative assessment, whereas its qualitative connotation remains unclear. The Three-River Headwaters Region (TRHR), which gives rise to the Yangtze, Yellow, and Lantsang–Mekong rivers, is critical to the water supply of several hundred million people downstream, so an accurate assessment of its water conservation function is essential. However, conventional assessment methods are systematically biased in cold regions because they do not adequately account for the low permeability of frozen ground or the seasonal storage and release of snow. Here we define the water conservation function of the TRHR in both quantitative and qualitative terms (water conservation volume and water conservation capacity). On this basis, a revised InVEST Seasonal Water Yield model was selected and its parameters localized, and the model was further validated using isotope-based runoff source analysis results. The results show that (1) from 1981 to 2020 the mean annual water conservation volume of the TRHR was 123.4 mm (451.6 × 10⁸ m³), increasing at 0.6 mm/a overall, with areas of increasing and decreasing trends accounting for 63.5% and 36.5% of the region, respectively; (2) water conservation capacity (mean 0.79) first declined and then recovered, was lower in the north and higher in the south, and declined mainly in seasonally frozen ground; and (3) water conservation volume was positively regulated by precipitation and negatively by evapotranspiration. Water conservation capacity varied with air temperature (positive below 0 °C and negative above 0 °C), elevation (negative), NDVI (positive), and freezing depth (negative), and ranked by land cover as marsh > forest > high/medium/low-cover grassland > cropland > bare land > desert. This framework can serve as a reference for assessing the water conservation function of the TRHR.

The Qilian Mountains, a crucial ecological security barrier and water conservation region in northwestern China, are highly sensitive to climate change. Reliable climate projections are essential for regional environmental management, yet the performance of statistical downscaling methods in this complex mountainous region remains inadequately evaluated. This study evaluates four statistical downscaling methods—Delta Change Method (DCM), Quantile Mapping (QM), Multiple Linear Regression (MLR), and Random Forest (RF)—using station-based observations (1951–2025) and outputs from 34 CMIP6 climate models. Validation results indicate that RF achieved the highest R ² and the lowest RMSE for both temperature and precipitation, with superior stability across models, scenarios, and stations. Based on RF downscaling, future climate projections under SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5 indicate a persistent warming and moderate wetting trend throughout the 21st century. Temperature is projected to increase at rates of 0.03 °C–0.31 °C/decade, while precipitation is projected to increase by approximately 3.2%–8.1% by the end of the century, although inter-model uncertainty remains substantial. Future climate change also exhibits pronounced seasonal and spatial heterogeneity, characterized by winter-dominated warming, reduced summer precipitation but increased autumn–winter precipitation, and strong elevation-dependent responses concentrated in high-elevation areas. The 0 °C isotherm is projected to rise by approximately 100–400 m by the late 21st century. These findings highlight the applicability of RF downscaling for station-scale climate projections in the Qilian Mountains and provide scientific support for regional climate adaptation, water resource management, and ecosystem conservation.

The spatiotemporal changes and driving mechanisms of rain-on-snow (ROS) events and their intensities are crucial for responding to disasters triggered by such events. However, there is currently a lack of detailed assessment of the seasonal variations and driving mechanisms of ROS events and their intensities in China. Therefore, this study utilized daily meteorological data and daily snow depth data from 513 stations in China during 1978–2020 to investigate spatiotemporal variations of ROS events and their intensities. Also, based on the detrend and partial correlation analysis model, the driving factors of ROS events and their intensity were explored. The results showed that ROS events primarily occurred in northern Xinjiang, the Qinghai–Tibet Plateau, Northeast China, and central and eastern China. ROS events frequently occurred in the middle and lower Yangtze River Plain in winter but were easily overlooked. The number and intensity of ROS events increased significantly (p < 0.05) in the Changbai Mountains in spring and the Altay Mountains and the southeast part of the Qinghai–Tibet Plateau in winter, leading to heightened ROS flood risks. However, the number and intensity of ROS events decreased significantly (p < 0.05) in the middle and lower Yangtze River Plain in winter. The driving mechanisms of the changes for ROS events and their intensities were different. Changes in the number of ROS events and their intensities in snow-rich regions were driven by rainfall days and quantity of rainfall, respectively. In regions with more rainfall, these changes were driven by snow cover days and snow water equivalent, respectively. Air temperature had no direct impact on ROS events and their intensities. These findings provide reliable evidence for responding to disasters and changes triggered by ROS events.

Water storage (WS) is a crucial terrestrial ecosystems service function. In cold alpine regions (CAR), the cryosphere elements are important solid water resources, but the existing methods for quantitatively assessing WS usually ignore cryosphere elements. In this study, a revised Seasonal Water Yield model (SWY) in the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST), which considers the effects of frozen ground (FG) and snow cover (SC) on WS, was employed to estimate the spatiotemporal distribution and changes in WS in the Three-Rivers Headwaters region (TRHR) from 1981 to 2020. Sensitivity analyses were conducted to understand the overall effects of multiple factors on WS, as well as the dominant driving factors of WS change at the grid scale in the TRHR. The results show that (1) the WS in the TRHR generally increased from 1981 to 2020 (0.56 mm/year), but the spatial distribution of WS change varied greatly, with a significant increasing trend in the northwest part and a significant decreasing trend in the southeast part. (2) In the last 40 years, increased precipitation (Pre) positively affected WS, while increased potential evapotranspiration (ET₀) reduced it. Increased permeability caused by degradation of frozen ground increased WS, while snow cover and LULC changes reduced it. (3) In the TRHR, Pre primarily affected the WS with the largest area ratio (32.62%), followed by land use/land cover (LULC) (19.69%) and ET₀ (18.49%), with FG being fourth (17.05%) and SC being the least (6.64%). (4) The highly important and extremely important zones generally showed a decreasing trend in WS and should be treated as key and priority conservation regions. It is expected that this research could provide a scientific reference for water management in the TRHR.

Watershed management requires reliable information about hydrologic ecosystem services (HESs) to support decision-making. In cold alpine regions, the hydrology regime is largely affected by frozen ground and snow cover. However, existing special models of ecosystem services usually ignore cryosphere elements (such as frozen ground and snow cover) when mapping water yield, which limits their application and promotion in cold alpine regions. By considering the effects of frozen ground and snow cover on water yield, a new version of the Seasonal Water Yield model (SWY) in the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) was presented and applied in the Three-River Headwaters Region (TRHR) in southeastern Qinghai-Tibetan Plateau (QTP). Our study found that incorporating the effects of frozen ground and snow cover improved model performance. Frozen ground acts as a low permeable layer, reducing water infiltration, while snow cover affects water yield through processes of melting and sublimation. Both of these factors can significantly impact the distribution of spatial and temporal quickflow and baseflow. The annual average baseflow and water yield of the TRHR would be overestimated by 13 mm (47.58 × 10⁸ m³/yr) and 14 mm (51.24 × 10⁸ m³/yr), respectively, if the effect of snow cover on them is not considered. Furthermore, if the effect of frozen ground on water yield were not accounted for, there would be an average of 6 mm of quickflow misestimated as baseflow each year. Our study emphasizes that the effects of frozen ground and snow cover on water yield cannot be ignored, particularly over extended temporal horizons and in the context of climate change. It is crucial to consider their impacts on water resources in cold alpine regions when making water-related decisions. Our study widens the application of the SWY and contributes to water-related decision-making in cold alpine regions.

Understanding the spatio-temporal variations in the frost-free period (FFP) and the number of frost days (FD) is beneficial to reduce the harmful effects of climate change on agricultural production and enhancing agricultural adaptation. However, the spatio-temporal variations in FFP and FD and their response to climate change remain unclear across China. To investigate the impact of climate change on FFP and FD, the trends and variations in FFP and FD across China from 1950 to 2020 were quantified using ERA5-Land, a reanalysis dataset with high spatial and temporal resolution. The results showed that ERA5-Land has good applicability in quantifying the trends and variations in FFP and FD across China under climate change. The spatial distribution of multi-year average FFP and FD across China showed significant latitudinal zonality and altitude dependence, i.e., FFP decreased with increasing latitude and altitude, while FD increased with increasing latitude and altitude. As a result of climate warming across China, the FFP showed an increasing trend with an increase rate of 1.25 d/10a and the maximum increasing rate of FFP in the individual region was 6.2 d/10a, while the FD showed a decreasing trend with a decrease rate of 1.41 d/10a and the maximum decreasing rate of FD in the individual region was −6.7 d/10a. Among the five major climate zones in China, the subtropical monsoon climate zone (SUMZ) with the greatest increasing rate of 1.73 d/10a in FFP, while the temperate monsoon climate zone (TEMZ) with the greatest decreasing rate of −1.72 d/10a in FD. In addition, the coefficient of variation (C_v) of FFP showed greater variability at higher altitudes, while the C_v of FD showed greater variability at lower latitudes in southern China. Without considering the adaptation to temperature of crops, a general increase in FFP and a general decrease in FD were both beneficial to agricultural production in terms of FFP and FD promoting a longer growing period and reducing frost damage on crops. This study provides a comprehensive understanding of the trends and variations in FFP and FD under climate change, which is of great scientific significance for the adjustment of the agricultural production layout to adapt to climate change in China.

Aim: Although protected areas (PAs) are assumed to reduce natural threats within boundaries, their spillover effects remain equivocal. It is necessary to determine whether PAs truly achieve conservation targets and whether they promote or inhibit natural habitat degradation in adjacent areas by blockage or leakage spillover. This study aims to choose 54 nature reserves (NRs) focusing on forest protection as a case study to assess PA conservation effectiveness and spillover prevalence.Location: PAs on the Qinghai‐Tibet Plateau (QTP).Methods: We used matching methods to compare deforestation rates inside PAs and their 20 km buffer zones with matched control areas based on the Global Forest Change dataset from 2001 to 2019. We contrasted the effects of NRs with different management levels, ages and areas. We designed five concentric buffer zones to assess spillover change with distance and estimated potential drivers of the spillover effect to explain its directions and magnitudes.Results: 75.9% of the NRs were effective in preventing deforestation within their boundaries. NRs with different properties showed similar performance on forest conservation. Spillover effects were heterogeneous around NRs. One hundred and twenty‐two buffer zones had positive spillover ranging from 0.1% to 5.3%. One hundred and nineteen buffer zones had leakages from −8.84% to −0.1%. Blockages slightly outnumbered leakages at different distances, while leakages happened more frequently when we treated buffer zones as a whole spillover area. The linear model indicated NR age and population density of buffer zones were the most relevant predictors to spillover value.Main conclusions: Most PAs performed well in forest conservation. Leakages could undermine or offset PA conservation efforts and were related to multiple natural or socio‐economic factors. We recommend considering the plurality of PAs as well as spillover effect and incorporating a social‐ecological framework in further PA establishment and management.

As a principal pathway of moisture loss of cryosphere, the sublimation of snow or ice needs to absorb a high amount of energy to complete the phase transition, while related researches on how sublimation affects surface energy balance (SEB) are still insufficient, causing unclear conclusions. To characterize the seasonal variation of a mountain glacier's sublimation or evaporation and analysis its role on SEB, the meteorological and glaciological data over five‐year measurement period (2016–2020) were obtained on the top of August‐one glacier. In the non‐melt period of a year (January–May and October–December), sensible heat flux H was the dominant energy contributor to glacier surface (76%), followed by net radiation R _net (22%). Sublimation removed average 85 mm (0.4 mm/day) of water vapor from surface for the dry and windy weather, and the latent heat flux of sublimation LEE accounted for 33% of energy sinks (67% of energy was stored in the glacier Q _s ). In the melt period (June–September), evaposublimation (mainly composed of evaporation) reached to 36 mm (0.3 mm/day), but LEE only played a small heat sink (14%) and the Q _m (the energy for melting) had the largest proportion (70%). R _net and H contributed 81% and 15% of surface energy, respectively. Obviously, under the global climate warming, the sublimation of non‐melt period seems to be effective in decrease the heating rate of glacier surface.

Glacial changes have great effects on regional water security because they are an important component of glacierized basin runoff. However, these impacts have not yet been integrated and evaluated in the arid/semiarid inland river basins of western China. Based on the degree-day glacier model, glacier changes and their hydrologic effects were studied in 12 subbasins in the Shiyang River basin (SYRB), Heihe River basin (HHRB) and Shule River basin (SLRB). The results showed that the glacier area of each subbasin decreased by 16.7–61.7% from 1965 to 2020. By the end of this century, the glacier areas in the three basins will be reduced by 64.4%, 72.0% and 83.4% under the three climate scenarios, and subbasin glaciers will disappear completely after the 2070s even under RCP2.6. Glacial runoff in all subbasins showed a decreasing–increasing–decreasing trend, with peak runoff experienced in 11 subbasins during 1965~2020. The contribution of glacial meltwater to total runoff in the basin ranged from 1.3% to 46.8% in the past, and it will decrease in the future due to increasing precipitation and decreasing glacial meltwater. However, the scale differences in glacier runoff are significant when aggregated over the region/basin/subbasin. This suggests that the results of large-scale generalization may be misleading for subbasin glacier water resource evaluations. Therefore, the hydrological effects of glaciers should be studied more in subbasins to provide an accurate reference for practical water resource management.

Positive degree-day (PDD) indicates the accumulated positive temperature in a given time period; it directly relates to the melting of snow and ice, and it is a key parameter between global warming and cryosphere changes. In this study, we calculated the PDD based on the daily mean temperatures from 1960 to 2018 at meteorological stations, and we used measured and interpolated data to determine spatial and temporal distribution and changes in PDD in western China (WC). Results show that the mean annual, warm season, and cold season PDD values at 209 meteorological stations were 3652.2, 2832.9, and 819.3 °C, respectively. PDD spatial distribution in WC is similar to that of air temperature. In WC, PDD mainly ranged from 0 to 5000, 1000 to 4000, and 0 to 1000 °C year⁻¹, respectively for annual, warm season, and cold season. From 1960 to 2018, the observed mean initial day of PDD moved forward by 8.3 days, and the final day was delayed by 8.2 days, with the duration expanding to 16.6 days; the trend in PDD reversed in the 1980s and the change rate in PDD for annual, warm season and cold season was 6.6, 3.8, and 2.7 °C year⁻¹, respectively. Regionally, PDD increased in almost all areas; the high PDD advanced from south to north, east to west, desert to mountain, and low to high altitudes. The results also showed that the warming rate of PDD was lower in the cold season and in high-altitude areas, which was opposite to the observed temperature patterns, however, the non-linear relationship between PDD and mean temperature over a period of time is the main reason for this phenomenon. This study adds more details for the understanding of climate change in WC, and suggests that more attention should be paid to PDD in the study of cryosphere changes.