Snow Cover Period Research Articles

Application of time-lapse digital imagery for ground-truth verification of satellite indices in the boreal forests of Alaska

Satellite remote sensing studies of snow cover in high-latitude boreal forests require ground-truth verification based on ground observation networks. In this study, we used time-lapse digital images to precisely detect the extent of snow cover at nine locations in the boreal forests of Alaska, and to demonstrate the relationship of these ground-truth measurements to satellite indices of snow cover. Our results show that normalized difference vegetation indices (NDVIs) and normalized difference water indices (NDWIs) show significant variations at the end and beginning periods of continuous snow cover: the NDVIs on the last days of continuous snow cover ranged from 0.12 to 0.37, and those on the first days of continuous snow cover ranged from 0.16 to 0.38. The normalized difference snow indices (NDSIs) were also positive during periods of continuous snow cover and negative during periods of no snow cover. The NDWIs varied significantly from the beginning to the end of periods of continuous snow cover. This study confirms that continuous snow cover is important for accurate phenological studies using NDVIs in the region of the trans-Alaska camera network. Simple cameras can be effectively utilized in ground-based networks, functioning not only as a ground-truth verification tools for calibrating satellite indices, but also as a source of data to fill data gaps in satellite records.

Spatiotemporal changes of snow cover over the Tibetan plateau based on cloud-removed moderate resolution imaging spectroradiometer fractional snow cover product from 2001 to 2011

Snow cover changes over the Tibetan plateau (TP) are examined using moderate resolution imaging spectroradiometer (MODIS) daily fractional snow cover (FSC) data from 2001 to 2011 as well as in situ temperature data. First, the accuracy of the MODIS FSC data under clear sky conditions is evaluated by comparing with Landsat 30-m observations. Then we describe a cloud-gap-filled (CGF) method using cubic spline interpolation algorithm to fill in data gaps caused by clouds. Finally, the spatial and temporal changes of snow cover are analyzed on the basis of the MODIS-derived snow-covered area and snow-covered days (SCD) data. Results show that the mean absolute error of MODIS FSC data under clear sky condition is about 0.098 over the TP. The CGF method is efficient in cloud reduction (overall mean absolute error of the retrieved FSC data is 0.092). There is a very high inter-annual and intra-seasonal variability of snow cover in the 11 years. The higher snow cover corresponds well with the huge mountains. The accumulation and melt periods of snow cover vary in different elevation zones. About 34.14% (5.56% with a significant decline) and 24.75% (3.9% with a significant increase) of the study area presents declining and increasing trend in SCD, respectively. The inter-annual fluctuation of snow cover can be explained by the high negative correlations observed between the snow cover and the in situ temperature, especially in some elevations of February, April, May, August, and September.

Confounded winter and spring phenoclimatology on large herbivore ranges

Annual variation in winter severity and growing season vegetation dynamics appear to influence the demography of temperate herbivores but parsing winter from spring effects requires independent metrics of environmental conditions specific to each season. We tested for independence in annual variation amongst four common metrics used to describe winter severity and early growing season vegetation dynamics across the entire spatial distribution of elk (Cervus elaphus) in Wyoming from 1989 to 2006. Winter conditions and early growing season dynamics were correlated in a specific way. Winters with snow cover that ended early tended to be followed by early, but slow, rises in the normalized difference vegetation index (NDVI), while long winters with extended periods of snow cover were often followed by late and rapid rises in NDVI. Across the 35 elk ranges, 0.4–86.8 % of the variation in the rate of increase in NDVI’s in spring was explained by the date snow cover disappeared from SNOTEL stations. Because phenoclimatological metrics are correlated across seasons and shifting due to climate change, identifying environmental constraints on herbivore fitness, particularly migratory species, is more difficult than previously recognized.

Characteristics of meltwater and/or rainfall regime in a snowy region and its effect on sediment-related disasters

Meltwater and/or rainfall (MR) were monitored using lysimeters in a mountainous region in the north-central part of Japan, where a seasonal snowpack forms, to collect basic data sets for understanding the MR regime and sediment-related disasters. Statistical analyses of the data over 11 years showed that high hourly MR intensities were mainly observed as rain during the non-snow cover period, but the annual maximum daily MR often occurred during the snow cover period. The longer the time unit, the greater the shift in maximum MR values from the non-snow to snow cover periods. For a time unit of 70 h, almost all maximum values were recorded during snow melting periods. The timing, intensity and duration of MR regulate the characteristics of sediment-related disasters such as debris flows, slope failures and landslides. In the case of deep-seated landslides, if there are no accurate observations of MR during the snow cover period, the degree of risk may be underestimated. Furthermore, when designing groundwater discharge works to prevent deep-seated landslides, the timing, intensity and duration of MR must be accurately evaluated to effectively discharge groundwater during the snow melting period.

Climate and site management as driving factors for the atmospheric greenhouse gas exchange of a restored wetland

Abstract. The atmospheric greenhouse gas (GHG) budget of a restored wetland in western Denmark was established for the years 2009–2011 from eddy covariance measurements of carbon dioxide (CO2) and methane (CH4) fluxes. The water table in the wetland, which was restored in 2002, was unregulated, and the vegetation height was limited through occasional grazing by cattle and grass cutting. The annual net CO2 uptake varied between 195 and 983 g m−2 and the annual net CH4 release varied between 11 and 17 g m−2. In all three years the wetland was a carbon sink and removed between 42 and 259 g C m−2 from the atmosphere. However, in terms of the full annual GHG budget (assuming that 1 g CH4 is equivalent to 25 g CO2 with respect to the greenhouse effect over a time horizon of 100 years) the wetland was a sink in 2009, a source in 2010 and neutral in 2011. Complementary observations of meteorological factors and management activities were used to explain the large inter-annual variations in the full atmospheric GHG budget of the wetland. The largest impact on the annual GHG fluxes, eventually defining their sign, came from site management through changes in grazing duration and animal stocking density. These changes accounted for half of the observed variability in the CO2 fluxes and about two thirds of the variability in CH4 fluxes. An unusually long period of snow cover in 2010 had the second largest effect on the annual CO2 flux, whose interannual variability was larger than that of the CH4 flux. Since integrated CO2 and CH4 flux data from restored wetlands are still very rare, it is concluded that more long-term flux measurements are needed to quantify the effects of ecosystem disturbance, in terms of management activities and exceptional weather patterns, on the atmospheric GHG budget more accurately.

Long-term variations of the seasonal snow cover in Nordland, Norway: the influence of the North Atlantic Oscillation

AbstractTemporal and spatial variations of the seasonal snow cover at 40 sites in Nordland county, Norway, since the last decade of the 19th century are examined. Nordland lies across the Arctic Circle. Annual maximum snow depths there have varied, reflecting the interaction of synoptic conditions, temperature and terrain. North/south and coastal/inland differences are evident, but common temporal trends are identified. Maximum snow depths are strongly related to the winter North Atlantic Oscillation index. Early in the 20th century, the index was positive and the associated stormy conditions resulted in a deep, prolonged snow cover. As the index declined in the 1920s, snow depths decreased sharply. Through much of the second half of the 20th century they increased as the index tended to become more positive. The start and duration of the period of continuous snow cover is influenced by the autumn NAO index. A decrease of duration around 1990 was particularly evident at low-lying stations and those in northern Nordland. The NAO has varied considerably over the past 120 years. Because of its influence, forecasting future trends of snow depth and snow-cover duration is not a simple task.

Influence of snow-cover and soil-frost variations on continuously monitored CO2 flux from agricultural land

Changes in cryospheric snow accumulation, snowmelt, and soil freezing and thawing might influence the ground-surface CO2 flux and cumulative winter CO2 flux from agricultural land. We continuously observed CO2 flux using automatically closing chambers at an untreated control plot and a plot with snow removal in northern Japan. The CO2 in soil pores at 10-cm depth increased by 6.5ppmvday−1 as soil began to freeze, but it increased dramatically (to 49ppmvday−1) after snowmelt water infiltrated the soil and froze. The soil-frost layer constrained gas diffusion into the air, and the barrier strengthened as the frozen snowmelt water decreased the air volume in soil pores. Leached gas CO2 from the freezing snowmelt water also increased gas CO2 concentration in soil. As the soil thawed, the CO2 concentration decreased drastically, at 790ppmvday−1. However, these changes had little effect on CO2 flux. The soil CO2 concentration remained stable after snow cover reached 30cm in the control plot. Low CO2 flux in both plots occurred during the winter. No clear relation was found between CO2 flux and snow depth or soil-frost depth because of the small CO2 source at this site. We also considered how the presence of the chamber influenced soil temperatures and water contents. During the snow-free season, the chamber mitigated diurnal changes in soil temperature. The daily average soil temperature differed from that in the natural state by −1.7°C to 6.3°C. This fluctuation of temperature corresponded to the fluctuation of CO2 flux, which ranged from 91% to 143% of the CO2 flux in the natural state based on the temperature-response equations. The chamber had little influence on the soil temperature during the snow-cover period, and did not influence soil water content throughout the study period. Cumulative winter CO2 emissions were 17.2gCm−2 (over 143 days) in the control plot and 13.4gCm−2 (over 151 days) in the treated plot (10.0 and 7.5% of annual accumulation, respectively).

Influence of snowmelt time on species richness, density and production in a late snowbed community

Within the alpine life zone, snowbeds are regarded as especially vulnerable to the predicted decrease in snowfall and may be considered as a suitable habitat for studies concerning the effects of global changes on alpine vegetation. This paper investigated the influences of snow-free period on species richness, density and primary production in a late snowbed dominated by the moss Polytrichastrum sexangulare. An historical average difference of 2.4 weeks in the release from snow cover did not affect either density or production of the dominant species. In contrast, vascular plant species richness was limited by the length of growing season, and some vascular species showed differences in density and production between late and early snow-free stands. Moreover, total vascular species production was found to be markedly higher in the early snow-free stands. These results suggest that, in this extreme habitat, vascular plant species richness, density and production are very responsive to variation in the snow cover period. Accordingly, both structural properties and functional processes in this habitat may be noticeably altered, within a climatic global change scenario.

Integral quantification of seasonal soil moisture changes in farmland by cosmic-ray neutrons

Abstract. Soil moisture at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. However, so far only a few methods are on the way to close this gap between point measurements and remote sensing. One new measurement methodology that could determine integral soil moisture at this scale is the aboveground sensing of cosmic-ray neutrons, more precisely of ground albedo neutrons. The present study performed ground albedo neutron sensing (GANS) at an agricultural field in northern Germany. To test the method it was accompanied by other soil moisture measurements for a summer period with corn crops growing on the field and a later autumn-winter period without crops and a longer period of snow cover. Additionally, meteorological data and aboveground crop biomass were included in the evaluation. Hourly values of ground albedo neutron sensing showed a high statistical variability. Six-hourly values corresponded well with classical soil moisture measurements, after calibration based on one reference dry period and three wet periods of a few days each. Crop biomass seemed to influence the measurements only to minor degree, opposed to snow cover which has a more substantial impact on the measurements. The latter could be quantitatively related to a newly introduced field neutron ratio estimated from neutron counting rates of two energy ranges. Overall, our study outlines a procedure to apply the ground albedo neutron sensing method based on devices now commercially available, without the need for accompanying numerical simulations and suited for longer monitoring periods after initial calibration.

Fidelity to Roost Sites and Diet Composition of Wintering Male Urban Common KestrelsFalco tinnunculus

Abstract. During harsh winters, partially migratory raptors face to making a decision whether leave their breeding sites or not. However, decision to leave brings advantages for maintaining own body condition, but also disadvantages for further reproduction. We studied individual variability in fidelity to roost sites during two winters. The kestrel males in Ceske Budějovice (Southern Bohemia) roost near their breeding sites for most of the winter. Individuals occupy the same roost site continuously, unless they temporarily leave the city. We collected pellets at the males' roost sites from November to April in 1996/1997 and 1997/1998. We analysed the factors that affect males' presence (proportion of days with snow cover — PSC, snow depth and mean temperature). There were fewer absences, overall, in 1997/1998 than in 1996/1997, probably due to milder weather conditions, and better prey availability. Individuals responded differently to periods of snow cover; some males left the city but others remained. ...

Local and regional photovoltaic power prediction for large scale grid integration: Assessment of a new algorithm for snow detection

ABSTRACTLarge‐scale grid integration of photovoltaic (PV) power requires forecast information on the expected PV power for all levels of electricity supply systems. Regional PV power forecasts provide the basis for grid management and trading of PV power on the energy market. On the local scale, smart grid applications define a sector with increasing need for PV power forecasting. Here, we present and evaluate new and enhanced features of the regional PV power prediction system of the University of Oldenburg and Meteocontrol GmbH. The basic approach to predict regional PV power with an hourly resolution of up to 2 days ahead is based on global model forecasts of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and includes explicit physical modelling steps to convert the predicted solar irradiance into PV power. The proposed new, empirical approach aims at improving PV power predictions during periods of snow cover, where the original forecasts usually show a strong overestimation of the power production. The approach integrates measured PV power production data and additional meteorological forecast parameters. The new approach for power forecasting has been evaluated against the operational forecasts for the control area of the German transmission system operator ‘50Hertz Transmission GmbH’ for a 1‐year period. The root mean square error (rmse) of the forecasts could be reduced from 4.9% to 3.9% for intra‐day forecasts, and from 5.7% to 4.6% for day‐ahead forecasts. The largest improvement was found during January, where the rmse could be reduced by more than half by applying the proposed algorithm for snow detection. Copyright © 2011 John Wiley & Sons, Ltd.

Evaluation of Moderate-resolution Imaging Spectroradiometer (MODIS) snow albedo product (MCD43A) over tundra

This study assesses the MODIS standard Bidirectional Reflectance Distribution Function (BRDF)/Albedo product, and the daily Direct Broadcast BRDF/Albedo algorithm at tundra locations under large solar zenith angles and high anisotropic diffuse illumination and multiple scattering conditions. These products generally agree with ground-based albedo measurements during the snow cover period when the Solar Zenith Angle (SZA) is less than 70°. An integrated validation strategy, including analysis of the representativeness of the surface heterogeneity, is performed to decide whether direct comparisons between field measurements and 500-m satellite products were appropriate or if the scaling of finer spatial resolution airborne or spaceborne data was necessary. Results indicate that the Root Mean Square Errors (RMSEs) are less than 0.047 during the snow covered periods for all MCD43 albedo products at several Alaskan tundra areas. The MCD43 1-day daily albedo product is particularly well suited to capture the rapidly changing surface conditions during the spring snow melt. Results also show that a full expression of the blue sky albedo is necessary at these large SZA snow covered areas because of the effects of anisotropic diffuse illumination and multiple scattering. In tundra locations with dark residue as a result of fire, the MODIS albedo values are lower than those at the unburned site from the start of snowmelt.

Modeling the impact of wintertime rain events on the thermal regime of permafrost

Abstract. In this study, we present field measurements and numerical process modeling from western Svalbard showing that the ground surface temperature below the snow is impacted by strong wintertime rain events. During such events, rain water percolates to the bottom of the snow pack, where it freezes and releases latent heat. In the winter season 2005/2006, on the order of 20 to 50% of the wintertime precipitation fell as rain, thus confining the surface temperature to close to 0 °C for several weeks. The measured average ground surface temperature during the snow-covered period is −0.6 °C, despite of a snow surface temperature of on average −8.5 °C. For the considered period, the temperature threshold below which permafrost is sustainable on long timescales is exceeded. We present a simplified model of rain water infiltration in the snow coupled to a transient permafrost model. While small amounts of rain have only minor impact on the ground surface temperature, strong rain events have a long-lasting impact. We show that consecutively applying the conditions encountered in the winter season 2005/2006 results in the formation of an unfrozen zone in the soil after three to five years, depending on the prescribed soil properties. If water infiltration in the snow is disabled in the model, more time is required for the permafrost to reach a similar state of degradation.

Distribution and larval habitats of Anopheles species in northern Gyeonggi Province, Republic of Korea

A total of 180 larval collection sites (e.g., rice paddies, marshes, ground pools, ponds, stream margins, and irrigation and drainage ditches) was surveyed within a 2 km radius from Warrior Base training area, 5 km south of Panmunjeom (Joint Security Area, demilitarized zone), Gyeonggi Province, Republic of Korea (ROK), from May through October, 2007 to characterize larval habitat distributions of members of the Anopheles Hyrcanus Group (An. sinensis, An. lesteri, An. pullus, An. belenrae, An. kleini, and An. sineroides). A total of 5,859 anopheline larvae was collected from 84.4% of the sites surveyed, of which 4,071 were identified to species by polymerase chain reaction (PCR) using the ribosomal DNA internal transcribed spacer 2 (rDNA ITS2). Anopheles sinensis (52.6%) was the most frequently collected, followed by An. kleini (29.4%), An. sineroides (9.8%), An. pullus (6.7%), An. belenrae (1.1%), and An. lesteri (0.5%). Anopheles pullus and An. kleini were collected in greater proportions in May and from May - July, respectively. Few An. sinensis were collected from May - June, but it was the predominant species collected by August, and accounted for >80% of all larvae from September - October. Anopheles kleini was found in all habitats sampled; however, it was collected most frequently in young growth rice paddies, while An. sinensis was collected more frequently in mature and post-harvest paddies. Anopheles pullus was associated with pre-cultivated rice paddies, including water-filled tire ruts left from the previous fall's harvest.

Evaluation of a cloud-gap-filled MODIS daily snow cover product over the Pacific Northwest USA

Summary The cloud-gap-filled (CGF) method developed by Hall et al. (2010) is a novel method for efficiently mitigating cloud obscuration using the most recently available cloud-free observations from prior days at each pixel. In this paper, we extend this method not only using prior observations but also using subsequent observations. Four CGF using 3 or 5 days prior or subsequent observations are applied to the standard MODerate resolution Imaging Spectroradiometer (MODIS) snow cover product and are evaluated against 3-years, in situ observations at 244 SNOwpack TELemetry (SNOTEL) stations. Results indicate that daily CGF snow cover maps using prior or subsequent observations are obviously different due to daily cloud shifting. However, the monthly and annual cloud reductions are similar. Although the overall accuracies under all-sky conditions of CGF using prior or subsequent observations are very similar, CGF snow cover maps using subsequent images have less underestimation errors, except during the snow melting period, and higher snow accuracies. When the observation interval is expanded from 3 to 5 days, this method is able to fill more cloud obscurations and increase the overall accuracies by ∼30% and ∼37%, respectively; however, they introduce slightly more uncertainty. Monthly and regional analyses indicate that this method is more efficient during the snow-covered period or in high-elevation zones.

Ecosystem Respiration in a Seasonally Snow-Covered Subalpine Grassland

Ecosystem respiration is important because it is the small imbalances between CO2 uptake via photosynthesis and CO2 release by ecosystem respiration that determine the effect of the biosphere on atmospheric CO2. For subalpine grasslands with mild winters we do not know the size of under-snow respiration relative to the total annual ecosystem respiration. This study determines the contribution of respiration through snow to total annual respiration, and models annual ecosystem respiration based on relationships with soil temperature and water content. Measurements were made monthly for two years in an unmanaged subalpine grassland in the Snowy Mountains of Australia. The vegetation is sparse (aboveground mass = 355–605 g m−2, belowground mass = 570–1010 g m−2) and dominated by native perennial C3 grasses and sedges. Ecosystem respiration was positively related to temperature, and there was some evidence that ecosystem respiration was more temperature sensitive at temperatures between 0 and 2 °C than at warmer temperatures. Annual ecosystem respiration was 12.1 Mg C ha−1 yr−1 in 2007/2008 and 10.5 Mg C ha−1 yr−1 in 2008/2009. Maximum daily rates of ecosystem respiration of 7 µmol CO2 m−2 s−1 occurred during summer, while minimum rates occurred under snow cover and were 0.2 to 0.9 µmol CO2 m−2 s−1. The duration of permanent snow cover was 60–68 days (equivalent to 16–18% of the year) and ecosystem respiration under snow was 4.1 to 4.3% of annual ecosystem respiration, which is smaller than the 10–50% commonly reported from studies in areas with longer snow-covered periods.

Influences of snow cover and soil-frost on ground surface flux and soil gas concentration of CO2 in an agricultural land in northern Japan

Our main objective was to elucidate how snow cover and soil frost influenced CO2 dynamics over agricultural land. We observed the CO2 flux above the soil or snow surface continuously using the commonly used static-chamber method and the CO2 concentration in the soil on snow-removal plot and untreated control plot over agricultural land in northern Japan from September 25, 2009, to May 31, 2010. The recorded largest CO2 flux was 3.9 μmol m-2 s-1 and CO2 concentration in soil was 390-5000 ppm. Little CO2 flux was observed during the soil-freezing and snow-covered periods. The CO2 concentration had been increasing about 10 ppm day-1 during the soil-freezing period at the snow-removal plot. At the beginning of April, the CO2 flux increased temporarily up to 0.19 μmol m-2 s-1 after the snow melted entirely at the untreated control plot and up to 0.52 μmol m-2 s-1 after the soil had thawed at the snow-removal plot. Snow-melting and soil-thawing largely influenced on CO2 flux, irrespective of soil temperature. The data were not explained by conventionally used temperature response functions for CO2 fluxes in these periods.

A reconstruction of annual mass balances of Austria’s glaciers from 1969 to 1998

AbstractAnnual glacier mass balances are reconstructed for 96% of the Austrian glacier-covered area (451 of 470 km2) between 1969 and 1998. The volume change derived from two complete glacier inventories (1969 and 1998) serves as the boundary condition that is aimed to be reproduced. ERA-40 reanalysis data as well as a gridded precipitation dataset (HISTALP) are used to drive a positive degree-day (PDD) model. The results are verified with four independent long-term mass-balance series. The spatial and vertical distribution of the tuning parameters is altered in order to reproduce the measured mean annual surface mass balances of selected glaciers, and a strong correlation is found between the median elevation of a glacier and the degree-day factor (DDF) at this elevation. This result implies that the lower a glacier’s median elevation is, the less melt occurs at a given elevation and temperature. We attribute this to the fact that lower-altitude glaciers are generally those with more accumulation, which leads to later exposure of bare ice and a longer period of high-albedo snow cover. A further improvement of the model was achieved by making DDF a function of time as well as space. The results indicate that mean DDFs generally increase for a given date over a sequence of consecutive negative mass-balance years, which probably reflects the reduction in albedo related to that. Finally, the major drivers of the observed mass-balance evolution are investigated: summer PDD sums correlate significantly better with the observed mass-balance changes than annual PDD sums or precipitation do. This implies that annual mass balances in the study area are governed by summer temperatures.

Measurement of dissolved CO2 transport by snowmelt runoff in paddy fields

The quantity of CO2 carried away by snowmelt during the thawing of a deposited snow layer was measured in an area subject to seasonal accumulation of snow. The concentration of dissolved CO2 was measured in snowmelt discharged from the outlet of a paddy field with heavy clay soil in Joetsu City, Niigata Prefecture, Japan. Samples were taken every few hours over a period of three days. The CO2 flux Fwater transported by the snowmelt was estimated from changes in the concentration of dissolved CO2, with the CO2 concentration continuously measured at the bottom of the deposited snow layer, and the quantity of snowmelt estimated from heat balance measurements. The ratio of the CO2 concentration, Csnow, to that dissolved in the snowmelt, Cwater, gradually decreased as the quantity of snow melted per unit time increased. Therefore, assuming this ratio to be proportional to the inverse of the snowmelt flow speed, a regression was carried out, based on the fact the flow speed is proportional to the quantity of melted snow per unit time raised to a power of 2/3. To assess the validity of the estimated Fwater, we studied the balance of CO2 in the deposited snow layer by using the CO2 store in the deposited snow. The quantity value of the soil respiration flux estimated from the balance of CO2 in the deposited snow layer was close to the average soil respiration flux during the snow-covered period estimated by the CO2 concentration gradient and the volume fraction of air in the snow layer previously deposited in the same paddy field.

Growth of Alpine Lady-Fern (Athyrium distentifolium) and Plant Species Composition on a Ski Piste in the Hrubý Jeseník Mts., Czech Republic

This study was focused on identifying the impact of a ski piste on snow conditions, soil temperature, as well as phenological development and growth of Athyrium distentifolium, and examining differences in species composition between the ski piste and the natural environment. Longer snow-cover period and deeper snow were observed on the ski piste than in the natural surroundings. Lower soil temperature was found on the ski piste during the peak winter period and at the beginning of the growing period. Different environmental conditions on the ski piste caused a delay and shortening of the phenological development of A. distentifolium in the late spring. Individuals of that plant caught up the initial delay in phenological development within 36 days after the beginning of measurement. However, plants only grew to lower height on ski piste as compared with plants in control plots. Even relatively small differences in the time of snow melt and soil temperature development in stands examined on the ski piste ...