Snowmelt Water Research Articles

Surface flow of melted snow water on the central Russian upland

In areas with a pronounced relief, water erosion causes great harm to agriculture and other sectors of the national economy. It leads to the destruction of the soil cover, a reduction in the area of arable land, a decrease in fertility, the removal of erosion products into floodplains, the siltation of ponds and rivers and the destruction of the road network. The scientific goal was to identify the influence of the main natural factors (snow reserves, freezing and soil moisture) on the formation of the spring melt water runoff on the plow. To study the questions raised, the water-balance method was used with the use of runoff sites. Observations showed that the formation of the melt water runoff depended on the depth of soil freezing. With shallow soil freezing up to 50 cm, there was no runoff. All the melt water was absorbed by the soil. As a result of 30 years of research (1991-2020), it was found that the average annual runoff on the plow was very weak - 3.8 mm on the scale of Surmach, the runoff coefficient is 0.05, shallow soil freezing - 19-28 cm, duration of snow melting - 16 days.

Temporal/Spatial Variation of Terrestrial Water Storage and Groundwater Storage in Typical Inland River Basins of Central Asia

In this study, the Amu Darya river basin, Syr Darya river basin and Balkhash lake basin in Central Asia were selected as typical study areas. Temporal/spatial changes from 2002 to 2016 in the terrestrial water storage (TWS) and the groundwater storage (GWS) were analyzed, based on RL06 Mascon data from the Gravity Recovery and Climate Experiment (GRACE) satellite, and the sum of soil water content, snow water equivalent and canopy water data that were obtained from Global Land Data Assimilation System (GLDAS). Combing meteorological data and land use and cover change (LUCC) data, the joint impact of both human activities and climate change on the terrestrial water storage change (TWSC) and the groundwater storage change (GWSC) was evaluated by statistical analysis. The results revealed three findings: (1) The TWS retrieved by CSR (Center for Space Research) and the JPL (Jet Propulsion Laboratory) showed a decreasing trend in the three basins, and the variation of TWS showed a maximum surplus in spring (March–May) and a maximum deficit in autumn (September–November). (2) The decreasing rates of groundwater storage that were extracted, based on JPL and CSR Mascon data sets, were −2.17 mm/year and −3.90 mm/year, −3.72 mm/year and −4.96 mm/year, −1.74 mm/year and −3.36 mm/year in the Amu Darya river basin, Syr Darya river basin and Balkhash lake basin, respectively. (3) In the Amu Darya river basin, annual precipitation showed a decreasing trend, while the evapotranspiration rate showed an increasing trend due to an increasing temperature, and the TWS decreased from 2002 to 2016 in most areas of the basin. However, in the middle reaches of the Amu Darya river basin, the TWS increased due to the increase in cultivated land area, water income from flooded irrigation, and reservoir impoundment. In the upper reaches of the Syr Darya river basin, the increase in precipitation in alpine areas leads to an increase in glacier and snow meltwater, which is the reason for the increase in the TWS. In the middle and lower reaches of the Syr Darya river basin, the amount of evapotranspiration dissipation exceeds the amount of water replenished by agricultural irrigation, which leads to a decrease in TWS and GWS. The increase in precipitation in the northwest of the Balkhash lake basin, the increase in farmland irrigation water, and the topography (higher in the southeast and lower in the northwest) led to an increase in TWS and GWS in the northwest of the Balkhash lake basin. This study can provide useful information for water resources management in the inland river basins of Central Asia.

Diurnal and seasonal dynamics of the electrical conductivity of water of the northeastern part of the Great Vasyugan Mire (Western Siberia)

In this study, we determined the diurnal and seasonal dynamics of the electrical conductivity of waters of the northeastern part of the Great Vasyugan Mire in Western Siberia. Our studies showed that the electrical conductivity of the waters for the period of April to September 2016 was characterised by a value of 35 μS/cm, and the seasonal amplitude was 25 μS/cm. In seasonal dynamics, there are three maximums of electrical conductivity in waters. The first maximum was formed in April (48 μS/cm) and is associated with snowmelt water supply. The second one was observed in May after the complete thawing of the peat deposit (39 μS/cm), and the third was observed at the end of July as a result of biochemical processes in the peat deposit (43 μS/cm). Our studies have shown the electrical conductivity hysteresis during time intervals from 3–5 to 6–10 days electrical conductivity remains constant despite the change in hydrometeorological conditions (water table level, temperature).

Spatial and Annual Variation in Microbial Abundance, Community Composition, and Diversity Associated With Alpine Surface Snow.

Understanding microbial community dynamics in the alpine cryosphere is an important step toward assessing climate change impacts on these fragile ecosystems and meltwater-fed environments downstream. In this study, we analyzed microbial community composition, variation in community alpha and beta diversity, and the number of prokaryotic cells and virus-like particles (VLP) in seasonal snowpack from two consecutive years at three high altitude mountain summits along a longitudinal transect across the European Alps. Numbers of prokaryotic cells and VLP both ranged around 104 and 105 per mL of snow meltwater on average, with variation generally within one order of magnitude between sites and years. VLP-to-prokaryotic cell ratios spanned two orders of magnitude, with median values close to 1, and little variation between sites and years in the majority of cases. Estimates of microbial community alpha diversity inferred from Hill numbers revealed low contributions of common and abundant microbial taxa to the total taxon richness, and thus low community evenness. Similar to prokaryotic cell and VLP numbers, differences in alpha diversity between years and sites were generally relatively modest. In contrast, community composition displayed strong variation between sites and especially between years. Analyses of taxonomic and phylogenetic community composition showed that differences between sites within years were mainly characterized by changes in abundances of microbial taxa from similar phylogenetic clades, whereas shifts between years were due to significant phylogenetic turnover. Our findings on the spatiotemporal dynamics and magnitude of variation of microbial abundances, community diversity, and composition in surface snow may help define baseline levels to assess future impacts of climate change on the alpine cryosphere.

The role of snowmelt discharge to runoff of an alpine watershed: Evidence from water stable isotopes

Snow is an important form of water storage which profoundly affects the hydrological processes in alpine watersheds, especially the runoff during snowmelt period. As the strong impact of climate change, the concern about snowmelt water to runoff in alpine watersheds is dramatically growing. However, the studies are mainly focused on arid and semi-arid areas, the research on semi-humid regions sensitive to the climate change need to be strengthened. In this study, for evaluating the contribution of snowmelt water to runoff in snowmelt period, we calculated the stable isotope values (δD, δ18O and d-excess) of different water bodies including river, snow, rain, groundwater, and snowmelt water in the Erdaobaihe River watershed of Changbai Mountains area. The results indicated that the δ18O values of snowmelt water showed an increasing trend with increasing temperature, while the d-excess values of snowmelt water showed a decreasing trend. During the snowmelt period, the snow cover ratio varied from 20.31% to 0.02%. The contribution ratio of snowmelt water to runoff was from 14.4% to 59.8% with average of 42.60% and the total contribution discharge was about 36.56 × 106 m3, which was higher than inland mountainous areas as different elevation and climate. As the stable water source of river, the groundwater contributed 19.2–61.6% with average of 43.88%. The snowmelt water plays an important role in regional water balance. Owing to climate change, the snowfall period in Changbai Mountains was gradually shortening and extreme snowfall events were increasing. The results will provide evidence for further hydrological studies and help to plan future water management strategies in the alpine watershed.

Estimation of Infiltration Volumes and Rates in Seasonally Water-Filled Topographic Depressions Based on Remote-Sensing Time Series.

In semi-arid ecoregions of temperate zones, focused snowmelt water infiltration in topographic depressions is a key, but imperfectly understood, groundwater recharge mechanism. Routine monitoring is precluded by the abundance of depressions. We have used remote-sensing data to construct mass balances and estimate volumes of temporary ponds in the Tambov area of Russia. First, small water bodies were automatically recognized in each of a time series of high-resolution Planet Labs images taken in April and May 2021 by object-oriented supervised classification. A training set of water pixels defined in one of the latest images using a small unmanned aerial vehicle enabled high-confidence predictions of water pixels in the earlier images (Cohen’s Κ = 0.99). A digital elevation model was used to estimate the ponds’ water volumes, which decreased with time following a negative exponential equation. The power of the exponent did not systematically depend on the pond size. With adjustment for estimates of daily Penman evaporation, function-based interpolation of the water bodies’ areas and volumes allowed calculation of daily infiltration into the depression beds. The infiltration was maximal (5–40 mm/day) at onset of spring and decreased with time during the study period. Use of the spatially variable infiltration rates improved steady-state shallow groundwater simulations.

Higher plasticity of water uptake in spruce than larch in an alpine habitat of North-Central China

Understanding interspecific differences in tree water use will aid in the assessment of both tree-level ecophysiological adaptation to climate change and forecasts of forest dynamics. We investigated the seasonal variation of water sources between two co-occurring trees species with contrasting leaf phenology and rooting traits: the deciduous Larix principis-rupprechtii Mayr. and the evergreen Picea meyeri Rehd. et Wils. At weekly/biweekly intervals from September 2013 to October 2014 in the Luya Mountains in North-Central China, we collected and analyzed a total of approximately 2400 samples of δD and δ18O in tree xylem water, potential water sources for all study trees, and the contribution of water at different soil depths. Concurrently, we monitored leaf phenology by direct observation and wood phenology with the microcore method. Microcoring allowed us to trace intra-annual dynamics of word formation (i.e., onset, end, and maximum growth rate). These results, including a seasonal origin index, indicated that winter snowmelt water is sourced for growth initiation for both larch and spruce, although larch relies on it more than spruce. Larch and spruce mainly absorbed water from the same soil layer of 10–20 cm during the growing season (circa 38.9% and 37.5% of total water uptake, respectively). However, this potential inter-specific water competition did not increase until growth rates reached the maximum for the year; larch used more water from deeper soil layers while spruce used water generally equally from each soil layer. Unlike deeper-rooting larch, the more shallow-rooted spruce showed a greater ability to shift water uptake among various soil layers. This plasticity in water uptake was accompanied by tighter stomatal regulation, suggesting spruce growth is generally more tightly coupled to water availability. Such diverging species-specific water use strategies improve our knowledge on tree-level ecophysiological mechanisms, with implications for understanding ecosystem-level forest dynamics and potential resilience to environmental stress.

Prediction of municipality-level winter wheat yield based on meteorological data using machine learning in Hokkaido, Japan.

This study analyzed meteorological constraints on winter wheat yield in the northern Japanese island, Hokkaido, and developed a machine learning model to predict municipality-level yields from meteorological data. Compared to most wheat producing areas, this island is characterized by wet climate owing to greater annual precipitation and abundant snowmelt water supply in spring. Based on yield statistics collected from 119 municipalities for 14 years (N = 1,516) and high-resolution surface meteorological data, correlation analyses showed that precipitation, daily minimum air temperature, and irradiance during the grain-filling period had significant effects on the yield throughout the island while the effect of snow depth in early winter and spring was dependent on sites. Using 10-d mean meteorological data within a certain period between seeding and harvest as predictor variables and one-year-leave-out cross-validation procedure, performance of machine learning models based on neural network (NN), random forest (RF), support vector machine regression (SVR), partial least squares regression (PLS), and cubist regression (CB) were compared to a multiple linear regression model (MLR) and a null model that returns an average yield of the municipality. The root mean square errors of PLS, SVR, and RF were 872, 982, and 1,024 kg ha−1 and were smaller than those of MLR (1,068 kg ha−1) and null model (1,035 kg ha−1). These models outperformed the controls in other metrics including Pearson’s correlation coefficient and Nash-Sutcliffe efficiency. Variable importance analysis on PLS indicated that minimum air temperature and precipitation during the grain-filling period had major roles in the prediction and excluding predictors in this period (i.e. yield forecast with a longer lead-time) decreased forecast performance of the models. These results were consistent with our understanding of meteorological impacts on wheat yield, suggesting usefulness of explainable machine learning in meteorological crop yield prediction under wet climate.

東北地域日本海側の多雪地域における融雪水を利用した水稲の無コーティング種子代かき同時浅層土中播種栽培の苗立ちと生育，収量

東北地域日本海側の多雪地域における融雪水を利用した水稲の無コーティング種子代かき同時浅層土中播種栽培の苗立ちと生育，収量

Magmatic origin of geothermal fluids constrained by geochemical evidence: Implications for the heat source in the northeastern Tibetan Plateau

The northeastern Tibetan Plateau (NETP) represents the growth front of the Tibetan Plateau (TP) system. This region has long been recognized as a key in understanding the topographic response and crustal thickening of the entire TP. A heat flow anomaly (Gonghe Basin, 102 mW/m2) was found in the NETP. However, the heat-generation mechanism and the heat source of the Gonghe Basin are still debated as it is unclear whether they are related to magmatic melting activities. Herein, we provide systematic hydrogeochemical data of two types of geothermal waters (type I and II: geothermal waters sampled from within the basin and the mountainous regions, respectively) found in the region. Type I high δD (−85.0‰ to −59.0‰), δ18O (−11.1‰ to −8.0‰), Cl− (mostly range from 300 to 900 mg/L), and trace element, whereas type II has low δD (−97.1‰ to −89‰), δ18O (−13.0‰ to −11.8‰), Cl− (30 to 180 mg/L) and trace elements. Furthermore, we identified the existence of a high-temperature parent geothermal fluid based on the chloride – enthalpy model, it was estimated to possess a temperature of 310 °C and a circulation depth of 6.8–7.8 km. The parent geothermal fluid originated from snowmelt water, which later mixed with a magmatic fluid. The helium (He) ratios of geothermal gas ranged from 0.01 Ra to 0.18 Ra and indicated that the source of He was primarily from a crustal source. In addition to the heat flow analysis and magnetotelluric (MT) data, we suggested that the magmatic nature of the geothermal fluid is caused by a partial melt zone, which is ubiquitous in the middle to lower crust and serves as the heat source in the NETP. Finally, a conceptual model was built to illustrate the occurrence of magmatic fluid and its genesis. The findings will help to improve the understanding of the uplift of the TP and reveals the important role of deep groundwater circulation in the formation of high-temperature geothermal resources.

Sources and sinks of perchlorate in soil in coastal ice-free areas of Antarctica

Perchlorate (ClO4−), a persistent inorganic compound, has harmful effects on human health. Natural ClO4− is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO4− in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO4− in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO4− concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO4− in soil. Concentrations of ClO4− in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO4− in soil. Thus, atmospherically formed ClO4− is the main source for soil in Antarctica. In general, ClO4− concentrations (0.1–5.1 μg kg−1) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO4− in soil, and deeper depths for aqueous migration may contribute to the lower ClO4− concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO3−, no correlation between NO3− and ClO4− in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO4− concentrations in soil, suggesting that biological reduction is not an important sink for ClO4− in Antarctic soil.

Snow Lapse Rate Changes in the Atlas Mountain in Morocco Based on MODIS Time Series during the Period 2000–2016

The spatio-temporal distribution of snow cover metrics in a mountainous area is mainly related to the climatic conditions as well as to the prevailing morphological conditions. The present study aimed to investigate the altitudinal sensitivity of snow cover metrics using the MODIS Terra snow cover product (MOD10A1 v5). Annual snow metrics, including start of snow season (SOSS), end of snow season (EOSS), and snow cover duration (SCD) were extracted from snow-covered area (SCA) maps, which had been pre-processed using a cloud removal algorithm; the maps were of the Atlas Mountains, taken from the period of 2001–2016. In addition, a linear regression was applied to derive an annual altitudinal gradient for each snow metric in relation to various spatial scales in order to analyze the interdependency between snow and topography, and especially to assess the potential temporal trend of the snow gradient. Results indicated that elevation was the principal regulator of snow presence where snow was mostly accumulated above 2500 m. The annual altitudinal gradients for EOSS and SCD showed a marked negative trend beginning in 2007. However, the SOSS altitudinal gradient was marked by a positive trend. The mean SCD gradient for the entire Atlas Mountains decreased from 6 days/100 m to 3 days/100 m. This is a new and important finding since it may indicate the impact of climate change on the dynamics of snow metrics and provides guidance for water managers to better manage the snowmelt water with different terrain features.

Solid-phase extraction of alkylphosphonic and O-alkyl alkylphosphonic acids followed by HPLC separation using porous graphitic carbon sorbent

An HPLC separation of alkyl phosphonic acids on porous graphitic carbon adsorbent Hypercarb, based upon a step gradient of formic acid concentration in an aqueous mobile phase, was evaluated in this study. Analytes were detected by single quadrupole and triple quadrupole MS. Good separation was achieved for methyl phosphonic acid, ethylphosphonic acid, n-propylphosphonic acid, isopropylphosphonic acid, ethyl methylphosphonic acid, isopropyl methylphosphonic acid, isobutyl methylphosphonic acid, pinacolyl methylphosphonic acid. Solid-phase extraction of these analytes on Hypercarb was also proposed, desorption was carried out with aqueous ammonium formate and water-methanol mixtures. LODs were 0.1–0.2 ng mL−1 for these analytes without SPE; solid-phase extraction resulted in the decrease of LODs at least 100-fold. Accuracy was proven by analyses of spiked samples of river water and snow meltwater.

Hydrological effects of multiphase water transformation in Three-River Headwaters Region, China

The present study focuses on the influence of multiphase water transformation on the hydrology of the Three-River Headwater Region. Climatic factors, accelerated transformation of water bodies, and changes in runoff patterns were evaluated based on long-term field observations. Subsequently, we estimated that changes in climatic factors have prolonged the ablation period and accelerated warming since 1990. Additionally, the glacier retreat rate during 2001–2013 was accelerated by approximately 16.23% compared with that during 1976–2001, whereas the ratio of snowfall in annual precipitation has decreased by 2.37% since 1990. The beginning of the freezing cycles of lakes along with the complete cycles were delayed. Moreover, snow sublimation significantly increased after 1990. Amplitudes of frost days (number of days with daily minimum temperature below 0°C) during 1991–2019 were eight times higher than those during 1960–1990. Furthermore, the contribution of moisture recycling to precipitation increased by 9.74% from1979 to 1990 to 1991–2019. The variations in actual evaporation increased from −1.257 mm/a during 1980–1990 to 0.865 mm/a during 1991–2017 and the runoff increased by 66.83×108 m3/10a during 1991–2012. July experienced the highest rainfall and runoff. During the multiphase water transformation, the runoff recharge sources changed significantly, thus, changing the historical trend of recharge in the headwaters of rivers only by the glacier snow meltwater by providing a new recharge mode. However, the accelerated multiphase water transformation caused by climate warming increased the challenges in water resource management and flood control in alpine regions.

Measuring snow scavenging of two airborne cyclic volatile methylsiloxanes under controlled conditions

The objective of this study was to determine snow scavenging of cVMS and its potential effect on the cVMS concentrations in snowmelt water and surrounding soil. Snow scavenging of two cVMS, octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5), was examined in two steps. First, sorption and desorption of D4 and D5 on snowflakes, including snow sorption coefficients (KiA), were measured against a benchmark compound, cyclopentanone, at different temperatures from 0 to −20 °C. Measurements were made using a custom-made snow chamber and 14C-labeled D4 and D5. In addition, the transfer of snow-bound cVMS to snowmelt water and surrounding soil was studied with 14C-D4 and 14C-D5-spiked snowpack placed both in a closed snow chamber and on top of a layer of frozen soil in an open chemical hood. KiA values measured in both sorption and desorption processes were very small (<10−2 m). They increased with decreasing temperature and were higher for the D5 compared to D4. The calculated gas scavenging of D4 and D5 was small because of the small KiA values, while particle scavenging of cVMS is predicted to be negligible due to their low octanol/air partition coefficients (KOA). Most importantly, almost all 14C-D4 and 14C-D5 sorbed by a snowpack was lost during the snow melting process through re-volatilization and hydrolysis and became non-detectable in snowmelt water. In short, the experimental measurements demonstrated that snow scavenging could not be a valid deposition mechanism for these volatile hydrophobic compounds.

Concentration and Physical Characteristics of Black Carbon in Winter Snow of Beijing in 2015

In Beijing, the probability of snowfall is decreasing as a result of global warming. At the same time, Beijing has suffered severe air pollution. In this paper, the concentration and particle size characteristics of BC (Black Carbon) in snow during the winter of 2015 in Beijing were analyzed by the SP2 method. The average concentration of BC in snow meltwater in Beijing is 82 ng/mL, with a minimum value of 62.9 ng/mL and a maximum of 210.6 ng/mL. The BC particle size in snow and ice in the Beijing area is mostly concentrated in the range of 70–400 nm. After log-normal, the BC particle size above 600 nm is still small, which should be closely related to the nature of the local BC emission source. The concentration of BC in snow is highly susceptible to meteorological conditions and local pollution levels. When Beijing is under the control of the east wind or the southeast wind, aerosols in the urban areas can easily accumulate in the northwestern mountains and then settle or participate in the snowfall process, resulting in an increase in BC aerosol accumulation in the snow, thus further changing the optical properties of snow in the Beijing area.

Climate change decisive for Asia’s snow meltwater supply

Climate change decisive for Asia’s snow meltwater supply

Near-daily monitoring of surface temperature and channel width of the six largest Arctic rivers from space using GCOM-C/SGLI

Spatio-temporal changes in water temperature and discharge of the Arctic rivers are important variables to be observed not only for estimating runoff contributions from snow melt, rainfall, and thawing of permafrost over the continents but also for assessing their impacts on the Arctic sea-ice and marine ecosystem. Nevertheless, the number of ground water gauging stations and the frequency of in-situ measurements for temperature and discharge has been decreasing since the 20 Century due to the shrinkage of budgets for maintaining the in-situ stations. In this study, we explored the possibility to perform near-daily monitoring of river surface temperature (RST) and river channel width (RCW) from space using a Japanese satellite-borne optical sensor named SGLI which can observe radiances at the spectral bands from near-ultraviolet to thermal infrared regions at the same spatial resolution of 250-m on a global scale. River surface brightness temperature (RSBT) measured with SGLI TIR band was used as RST without atmospheric correction. RCW was derived as the widths of water pixels identified along river channels using SGLI reflectances at visible to shortwave infrared bands. Analysis results of two-year SGLI data acquired in 2018 and 2019 show that RSBT and RCW can be retrieved successfully from the SGLI observations on a daily basis after applying a spatio-temporal interpolation. The accuracies of the retrieved RSBT evaluated with in-situ water temperatures are about 2.57 K with the interpolation (and 1.84 K without the interpolation but with lower observation frequencies). Retrieved RCWs are correlated well with in-situ river water discharges indicating potentials to assess variations of not only snow melt water but also precipitation within the river basin. Thus, SGLI data can be used to reconstruct not only the river water temperature but also the river water discharges along the continental river channels for assessing heat flux flowing into the Arctic Ocean.

Linking soil water retention capacity to pore structure characteristics based on X-ray computed tomography: Chinese Mollisol under freeze-thaw effect

Studies have shown that the effects of freeze–thaw action on soil structure have become more frequent and intense with the global warming, in turn, affects the dynamic processes of snowmelt water and the development of soil erosion. To examine the effects of pore structure characteristics on soil water retention capacity under freeze–thaw cycles, soil samples of Chinese Mollisol were subject to the six freeze–thaw treatments, including a no freeze–thaw cycle (CK), one (FT.1), five (FT.5), ten (FT.10), fifteen (FT.15), and twenty (FT.20) freeze–thaw cycles. Then, the samples were scanned using industrial CT to quantitatively obtain soil structure characteristics, and a pressure plate apparatus was applied to obtain soil water retention capacity. The results show that the freeze–thaw cycles significantly changed the soil pore structure and soil water retention capacity. Freeze–thaw cycles increased the total imaged porosity and pore connectivity, leading to a complex pore structure and an irregular of pore shape. Relative to the CK treatment, soils under the FT.20 treatment exhibited a higher saturated water content (SWC) by 100.0%, but a lower field capacity (FC) by 14.0% and available water content (AWC) by 31.3%. No differences in the permanent wilting point (PWP) were found between the different treatments. The soil pore structure became more porous and complex with an increasing number of freeze–thaw cycles, resulting in the changes in soil water retention capacity. The porosities of 100–500 μm (Pd100–500) were a better predictor of SWC, with an increasing exponential function. The porosities of elongated pores (PE) predicted FC and AWC with a decreasing exponential function. These findings aim to improve the understanding of soil pore structure as a result of the effects of freeze–thaw on the generation mechanism of snowmelt runoff and soil erosion.

Contribution of Snow-Melt Water to the Streamflow over the Three-River Headwater Region, China

Snowmelt water is essential to the water resources management over the Three-River Headwater Region (TRHR), where hydrological processes are influenced by snowmelt runoff and sensitive to climate change. The objectives of this study were to analyse the contribution of snowmelt water to the total streamflow (fQ,snow) in the TRHR by applying a snowmelt tracking algorithm and Variable Infiltration Capacity (VIC) model. The ratio of snowfall to precipitation, and the variation of the April 1 snow water equivalent (SWE) associated with fQ,snow, were identified to analyse the role of snowpack in the hydrological cycle. Prior to the simulation, the VIC model was validated based on the observed streamflow data to recognize its adequacy in the region. In order to improve the VIC model in snow hydrology simulation, Advanced Scanning Microwave Radiometer E (ASMR-E) SWE product data was used to compare with VIC output SWE to adjust the snow parameters. From 1971 to 2007, the averaged fQ,snow was 19.9% with a significant decreasing trend over entire TRHR (p &lt; 0.05).The influence factor resulted in the rate of change in fQ,snow which were different for each sub-basin TRHR. The decreasing rate of fQ,snow was highest of 0.24%/year for S_Lantsang, which should be due to the increasing streamflow and the decreasing snowmelt water. For the S_Yangtze, the increasing streamflow contributed more than the stable change of snowmelt water to the decreasing fQ,snow with a rate of 0.1%/year. The April 1 SWE with the minimum value appearing after 2000 and the decreased ratio of snowfall to precipitation during the study period, suggested the snow solid water resource over the TRHR was shrinking. Our results imply that the role of snow in the snow-hydrological regime is weakening in the TRHR in terms of water supplement and runoff regulation due to the decreased fQ,snow and snowfall.