Earlier Snowmelt Onset Research Articles

Sources and pathways of spring flow and climate change effects in the Dungju Ri & Yude Ri catchments, Bhutan Himalaya

Springs and streams are vital water sources for supporting the livelihood of Himalayan residents. Escalating climate change, population growth, and economic development strain the region's freshwater resources. A national survey reveals declining spring and stream flows in Bhutan, necessitating an improved understanding of their generation. Monthly grab water samples were collected during April 2022–January 2023 from main streams, springs and other source waters at various elevations at Yude Ri and Dungju Ri catchments, Bhutan Himalayas. Samples were analyzed for pH, specific conductance, and major ions and end-member mixing analysis in combination with diagnostic tools of mixing models was used to determine sources, relative contributions, and recharge dynamics of spring flows. The results indicated that direct precipitation dominated spring flows (0.59 ± 0.21), followed by shallow groundwater (0.31 ± 0.18), and soil subsurface water (0.10 ± 0.15). The contributions of spring flow components followed an elevation gradient, with higher and lower fractions, respectively, of direct precipitation and shallow groundwater at higher elevations, e.g., 0.90 ± 0.1 to 0.13 ± 0.08 for direct precipitation and 0.03 ± 0.03 to 0.37 ± 0.19 for shallow groundwater from 3266 m to 1558 m. Spring flows primarily relied on precipitation (∼70 % from both direct precipitation and soil water), making them very sensitive to changes in precipitation. Significant contributions of shallow groundwater also indicated the vulnerability of spring flows to decreased snowfall relative to rainfall and the earlier onset of snowmelt, particularly for those located in the snow-rain transition zone (∼2500 m). Our results suggest high vulnerability of spring flows to the climate change in the Himalayas.

Sensitivity of seasonal air temperature and precipitation, and onset of snowmelt, to Arctic Dipole modes across the Taiga Plains, Northwest Territories, Canada

AbstractNorthern high latitudes are experiencing some of the greatest increases in air temperatures on Earth. Air temperatures (along with other modulating variables including precipitation and the onset of snowmelt) are influenced by atmospheric–oceanic circulation patterns, some of which are persistent and recurrent. One pattern in particular, the Arctic Dipole (AD) anomaly, is a persistent sea‐level pressure teleconnection pattern between the Canadian Archipelago and Barents Sea that has unknown impacts on local climate variability. These patterns may be important, especially in hydro‐ecologically sensitive areas such as Northwest Territories (NWT), Canada where permafrost thaw and ecosystem changes are influenced by interannual climate variability. The goal of this research is to determine the impacts of the AD on local climate (air temperature, precipitation, snowmelt) for a 66‐year period (1950–2015) spanning both latitudinal and longitudinal gradients across NWT from north to south and foothills to plains. Deviations during strong positive and negative modes of the AD index were calculated in reference to the complete 66‐year record. Results showed considerable year‐to‐year variability in the AD pattern, with more frequent strong negative modes during the 2000s. During 1950–2015, there were 64 and 56 occurrences of strong positive and strong negative AD modes, respectively, across all seasons. Spring and summer strong AD modes led to local air temperature anomalies of greater than 0.8°C compared with the long‐term (66 years) mean. Earlier onset of snowmelt, by an average of 3–5 days, was also noted during positive AD modes. Despite strong connectivity between the AD and local air temperature, we found less correspondence between the AD and seasonal precipitation. These findings improve understanding of the impacts of the AD on local weather and climate in NWT and suggest implications for ecosystem change, such as drying and shrubification of northern boreal peatlands and possible connectivity to teleconnection impacts on wildland fire.

Snowfall Fraction, Cold Content, and Energy Balance Changes Drive Differential Response to Simulated Warming in an Alpine and Subalpine Snowpack

Despite widespread warming in mountain regions, little research to date has explored the physical mechanisms driving the variable response of snowpacks to changes in climate, instead focusing primarily on empirical relationships such as seasonal air temperature or elevation. In this work, we evaluate how differences in snowfall fraction, cold content, and the snowpack energy balance produce simulated changes to snow accumulation and melt at an alpine and subalpine snowpack in the Niwot Ridge Long Term Ecological Research site. For our analysis, we created a 23 y baseline simulation using the SNOWPACK model forced by historical hourly meteorological data from water year 1991 through 2013. We then perturbed hourly air temperature in 0.5°C increments from +0.5°C to +4.0°C above baseline and increased incoming longwave radiation accordingly. For every 1°C of warming, peak snow water equivalent declined by 43.9 mm in the alpine and 54.3 mm in the subalpine, melt onset shifted 6.2 d earlier in the alpine and 8.8 d in the subalpine, the snow season shortened by 10.7 d in the alpine and 16.4 d in the subalpine, and melt rate increased by 0.2 mm d-1 in the alpine while decreasing by 0.4 mm d-1 in the subalpine. We found the alpine snowpack was less sensitive to warming for three primary reasons: 1) Snowfall fraction decreased less rapidly per 1°C of warming than in the subalpine; 2) Cold content still consistently developed throughout the snow season, preventing mid-winter melt events; 3) Changes to snowmelt rate were not significant because increases to the turbulent fluxes balanced decreases in the radiative fluxes with earlier snowmelt onset. Additionally, at 3°C of warming and greater, the subalpine site experienced a fundamental shift where significant melt could occur throughout the entirety of the winter as cold content was no longer large enough to buffer against positive energy fluxes. In some years, the subalpine snowpack became transient with several cycles of accumulation and melt per winter. This tipping point suggests sites with lower cold content—like the subalpine studied here—are likely to be more sensitive to producing increased winter melt as warming continues over the coming decades.

Hyporheic Zone Microbiome Assembly Is Linked to Dynamic Water Mixing Patterns in Snowmelt‐Dominated Headwater Catchments

AbstractTerrestrial and aquatic elemental cycles are tightly linked in upland fluvial networks. Biotic and abiotic mineral weathering, microbially mediated degradation of organic matter, and anthropogenic influences all result in the movement of solutes (e.g., carbon, metals, and nutrients) through these catchments, with implications for downstream water quality. Within the river channel, the region of hyporheic mixing represents a hot spot of microbial activity, exerting significant control over solute cycling. To investigate how snowmelt‐driven seasonal changes in river discharge affect microbial community assembly and carbon biogeochemistry, depth‐resolved pore water samples were recovered from multiple locations around a representative meander on the East River near Crested Butte, CO, USA. Vertical temperature sensor arrays were also installed in the streambed to enable seepage flux estimates. Snowmelt‐driven high river discharge led to an expanding zone of vertical hyporheic mixing and introduced dissolved oxygen into the streambed that stimulated aerobic microbial respiration. These physicochemical processes contributed to microbial communities undergoing homogenizing selection, in contrast to other ecosystems where lower permeability may limit the extent of mixing. Conversely, lower river discharge conditions led to a greater influence of upwelling groundwater within the streambed and a decrease in microbial respiration rates. Associated with these processes, microbial communities throughout the streambed exhibited increasing dissimilarity between each other, suggesting that the earlier onset of snowmelt and longer periods of base flow may lead to changes in the composition (and associated function) of streambed microbiomes, with consequent implications for the processing and export of solutes from upland catchments.

Spatiotemporal variability and decadal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometers

Abstract. The timing and intensity of snowmelt processes on sea ice are key drivers determining the seasonal sea-ice energy and mass budgets. In the Arctic, satellite passive microwave and radar observations have revealed a trend towards an earlier snowmelt onset during the last decades, which is an important aspect of Arctic amplification and sea-ice decline. Around Antarctica, snowmelt on perennial ice is weak and very different than in the Arctic, with most snow surviving the summer. Here we compile time series of snowmelt onset dates on seasonal and perennial Antarctic sea ice from 1992 to 2014/15 using active microwave observations from the European Space Agency's (ESA) European Remote Sensing (ERS) 1 and 2 missions (ERS-1 and ERS-2), Quick Scatterometer (QSCAT), and Advanced Scatterometer (ASCAT) radar scatterometers. We define two snowmelt transition stages: a weak backscatter rise, indicating the initial warming and destructive metamorphism of the snowpack (pre-melt), followed by a rapid backscatter rise, indicating the onset of thaw–freeze cycles (snowmelt). Results show large interannual variability, with an average pre-melt onset date of 29 November and melt onset of 10 December, respectively, on perennial ice, without any significant trends over the study period, consistent with the small trends of Antarctic sea-ice extent. There was a latitudinal gradient from early snowmelt onsets in mid-November in the northern Weddell Sea to late (end of December) or even absent snowmelt conditions in the southern Weddell Sea. We show that QSCAT Ku-band-derived (13.4 GHz signal frequency) pre-melt and snowmelt onset dates are earlier by 20 and 18 d, respectively, than ERS and ASCAT C-band-derived (5.6 GHz) dates. This offset has been considered when constructing the time series. Snowmelt onset dates from passive microwave observations (37 GHz) are later by 14 and 6 d than those from the scatterometers, respectively. Based on these characteristic differences between melt onset dates observed by different microwave wavelengths, we developed a conceptual model which illustrates how the seasonal evolution of snow temperature profiles may affect different microwave bands with different penetration depths. These suggest that future multi-frequency active and passive microwave satellite missions could be used to resolve melt processes throughout the vertical snow column of thick snow on perennial Antarctic sea ice.

Monitoring changes in forestry and seasonal snow using surface albedo during 1982–2016 as an indicator

Abstract. The surface albedo time series, CLARA-A2 SAL, was used to study trends in the snowmelt start and end dates, the melting season length and the albedo value preceding the melt onset in Finland during 1982–2016. In addition, the melt onset from the JSBACH land surface model was compared with the timing of green-up estimated from Moderate Resolution Imaging Spectroradiometer (MODIS) data. Moreover, the melt onset was compared with the timing of the greening up based on MODIS data. Similarly, the end of snowmelt timing predicted by JSBACH was compared with the melt-off dates based on the Finnish Meteorological Institute (FMI) operational in situ measurements and the Fractional Snow Cover (FSC) time-series product provided by the EU FP7 CryoLand project. It was found that the snowmelt date estimated using the 20 % threshold of the albedo range during the melting period corresponded well to the melt estimate of the permanent snow layer. The longest period, during which the ground is continuously half or more covered by snow, defines the permanent snow layer (Solantie et al., 1996). The greening up followed within 5–13 days the date when the albedo reached the 1 % threshold of the albedo dynamic range during the melting period. The time difference between greening up and complete snowmelt was smaller in mountainous areas than in coastal areas. In two northern vegetation map areas (Northern Karelia–Kainuu and Southwestern Lapland), a clear trend towards earlier snowmelt onset (5–6 days per decade) and increasing melting season length (6–7 days per decade) was observed. In the forested part of northern Finland, a clear decreasing trend in albedo (2 %–3 % per decade in absolute albedo percentage) before the start of the melt onset was observed. The decreasing albedo trend was found to be due to the increased stem volume.

Meltwater runoff in a changing climate (1951–2099) at Chhota Shigri Glacier, Western Himalaya, Northern India

ABSTRACTMeltwater runoff in the catchment area containing Chhota Shigri glacier (Western Himalaya) is simulated for the period 1951–2099. The applied mass-balance model is forced by downscaled products from four regional climate models with different horizontal resolution. For the future climate scenarios we use high resolution time series of 5 km grid spacing, generated using the newly developed Intermediate Complexity Atmospheric Research Model. The meteorological input is downscaled to 300 m horizontal resolution. The use of an ice flow model provides annually updated glacier area for the mass-balance calculations. The mass-balance model calculates daily snow accumulation, melt, runoff, as well as the individual runoff components (glacial melt, snowmelt and rain). The resulting glacier area decreases by 35% (representative concentration pathway (RCP) 4.5 scenario) to 70% (RCP 8.5 scenario) by 2099 relative to 2000. The average annual mass balance over the whole model period (1951–2099) was –0.4 (±0.3) m w.e. a–1. Average annual runoff does not differ substantially between the two climate scenarios. However, for the years after 2040 our results show a shift towards earlier snowmelt onset that increases runoff in May and June, and reduced glacier melt that decreases runoff in August and September. This shift is much stronger pronounced in the RCP 8.5 scenario.

On the variability of cold region flooding

Cold region hydrological systems exhibit complex interactions with both climate and the cryosphere. Improving knowledge on that complexity is essential to determine drivers of extreme events and to predict changes under altered climate conditions. This is particularly true for cold region flooding where independent shifts in both precipitation and temperature can have significant influence on high flows. This study explores changes in the magnitude and the timing of streamflow in 18 Swedish Sub-Arctic catchments over their full record periods available and a common period (1990–2013). The Mann–Kendall trend test was used to estimate changes in several hydrological signatures (e.g. annual maximum daily flow, mean summer flow, snowmelt onset). Further, trends in the flood frequency were determined by fitting an extreme value type I (Gumbel) distribution to test selected flood percentiles for stationarity using a generalized least squares regression approach.Results highlight shifts from snowmelt-dominated to rainfall-dominated flow regimes with all significant trends (at the 5% significance level) pointing toward (1) lower magnitudes in the spring flood; (2) earlier flood occurrence; (3) earlier snowmelt onset; and (4) decreasing mean summer flows. Decreasing trends in flood magnitude and mean summer flows suggest widespread permafrost thawing and are supported by increasing trends in annual minimum daily flows. Trends in selected flood percentiles showed an increase in extreme events over the full periods of record (significant for only four catchments), while trends were variable over the common period of data among the catchments. An uncertainty analysis emphasizes that the observed trends are highly sensitive to the period of record considered. As such, no clear overall regional hydrological response pattern could be determined suggesting that catchment response to regionally consistent changes in climatic drivers is strongly influenced by their physical characteristics.

Early snowmelt events: detection, distribution, and significance in a major sub-arctic watershed

High latitude drainage basins are experiencing higher average temperatures, earlier snowmelt onset in spring, and an increase in rain on snow (ROS) events in winter, trends that climate models project into the future. Snowmelt-dominated basins are most sensitive to winter temperature increases that influence the frequency of ROS events and the timing and duration of snowmelt, resulting in changes to spring runoff. Of specific interest in this study are early melt events that occur in late winter preceding melt onset in the spring. The study focuses on satellite determination and characterization of these early melt events using the Yukon River Basin (Canada/USA) as a test domain. The timing of these events was estimated using data from passive (Advanced Microwave Scanning Radiometer—EOS (AMSR-E)) and active (SeaWinds on Quick Scatterometer (QuikSCAT)) microwave remote sensors, employing detection algorithms for brightness temperature (AMSR-E) and radar backscatter (QuikSCAT). The satellite detected events were validated with ground station meteorological and hydrological data, and the spatial and temporal variability of the events across the entire river basin was characterized. Possible causative factors for the detected events, including ROS, fog, and positive air temperatures, were determined by comparing the timing of the events to parameters from SnowModel and National Centers for Environmental Prediction North American Regional Reanalysis (NARR) outputs, and weather station data. All melt events coincided with above freezing temperatures, while a limited number corresponded to ROS (determined from SnowModel and ground data) and a majority to fog occurrence (determined from NARR). The results underscore the significant influence that warm air intrusions have on melt in some areas and demonstrate the large temporal and spatial variability over years and regions. The study provides a method for melt detection and a baseline from which to assess future change.

Regional shifts in snowfall, melt in the intermountain west

The freshwater supplies of the American West rely, for the most part, on snow. The Colorado River, the Rio Grande, and other rivers in the intermountain west—bounded by the Sierra Nevada and Cascade mountains to the west and the Rockies to the east—are the main sources of water for one of the driest parts of the continent, and their flows are predominantly fed by the springtime melt of snow accumulated over the winter. With winter mean temperatures rising in some places by as much as 2.5°C in the past 2 decades, some scientists are concerned that the current hydrological regime of the region could be overthrown, with snow giving way to rain as the dominant form of precipitation. Decreasing snow accumulation and earlier snowmelt onset have been observed in Colorado. Whether these trends extend to the larger intermountain west region, however, is unknown.

Detection of changes in flow variability of the upper Danube between 1876-2006

It is widely acknowledged that global warming will result in an increased extremality of hydrological phenomena. As for streamflow it is anticipated that duration of low-flow conditions and flood frequency will both increase. Approving this hypothesis by statistically evaluating daily runoff characteristics depends on the availability of long and homogeneous data series. The aim of this paper is to analyze the change of the average daily flows of the Danube at Bratislava for different subsets of the period 1876-2006. The statistical tests did not reveal any increase in the extremality of daily runoff over the period 1876-2006. On the contrary, variability of daily flows of the Danube River decreases. Over the last 30 years streamflows increased in the winter-spring season and decreased in the summertime, compared to the past periods. This can be explained by the higher air temperature in the headwaters. A warmer climate causes an earlier onset of snowmelt in the winter-spring season, thus less runoff is observed in the summer with higher rates of precipitation.

Spatial and temporal variability of sea ice in the Laptev Sea: Analyses and review of satellite passive-microwave data and model results, 1979 to 2002

Satellite passive-microwave radiometer-derived sea-ice concentrations have been used to investigate the spatial and temporal variability and trends of sea ice in the Laptev Sea during 24 years from 1979 through 2002. The resulting time series have been further analyzed to provide a climatology for sea-ice and polynya characteristics. The ice regime of the Laptev Sea is characterized by a large seasonal and interannual variability, the latter occurring exclusively in summer. By using a consistent sea-ice data record, we can document negative trends in all the areas studied for the 24-year period, Due to the large interannual variability the trends are not significant. For the entire Laptev Sea the decreases in sea-ice extent and area on a yearly average basis reveal − 1.5% decade − 1 and − 1.7% decade − 1, respectively. In summer and early fall large losses in sea-ice cover of up to 7% decade − 1 are evident in regional sectors of the Laptev Sea. In addition, an increase in polynya activity in late winter and early spring, a significant shift towards earlier snowmelt onset, and an increase of open-water area in early fall indicating an extension of the length of the summer melt period, has been observed. A brief overview of climate and sea-ice research in the Siberian Arctic is presented. According to observational data and numerical experiments there is still a large degree of uncertainty about the role of dynamic and thermodynamic factors and possible feedback mechanisms in the atmosphere–ice–ocean system, which are responsible for the large interannual variability and the retreat of sea-ice coverage as observed in the 1990s. Summer sea-ice anomalies likely result from synoptic-scale processes superimposed by the large-scale atmospheric circulation during summer and to a lesser extent from preconditioning processes in winter and spring.

Spatial and temporal variability in snowmelt onset over Arctic sea ice

AbstractClimate models suggest surface warming in the Arctic will be rapid and pronounced, implying substantial changes in snowmelt onset are likely. This research therefore examines spatial and temporal variability in passive-microwave derived snow-melt-onset dates over Arctic sea ice. The objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt-onset record shows signs of climate change. Snowmelt-onset dates are derived with Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager brightness-temperature data, and they are subsequently stratified into 13 regions to analyze spatial and temporal variability. Results illustrate significant spatial variability in snowmelt onset, with the median annual snowmelt-onset date in one region of the Arctic typically being statistically different from most other regions. The examination of temporal variability also shows large interannual differences in the median snowmelt-onset date in most regions. Additionally, trends towards earlier snowmelt onset are documented in the West Central Arctic, Lincoln Sea, Beaufort Sea and Canadian Arctic Archipelago regions.