Snow Evaporation Research Articles

Observations of urban snow properties in Calgary, Canada

AbstractUrban winter hydrology has garnered very little attention owing to the general notion that high‐intensity rainfalls are the major flood‐generating events in urban areas. As a result, few efforts have been made to research urban snow and its melt characteristics. This study investigates the characteristics of urban snow that differentiate it from rural snow, and makes recommendations for incorporating these characteristics into an urban snowmelt model. A field study was conducted from the fall of 2001 to the spring of 2002 in the city of Calgary, Canada. Snow depths and densities, soil moisture, soil temperature, snow albedo, net radiation, snow evaporation, and surface temperature were measured at several locations throughout the winter period. The combination of urban snow removal practices and the physical elements that exist in urban areas were found to influence the energy balance of the snowpack profoundly. Shortwave radiation was found to be the main source of energy for urban snow; as a consequence, the albedo of urban snow is a very important factor in urban snowmelt modelling. General observations lead to the classification of snow as one of four types: snow piles, snow on road shoulders, snow on sidewalk edges, and snow in open areas. This resulted in the development of four separate functions for the changing snow albedo values. A study of the frozen ground conditions revealed that antecedent soil moisture conditions had very little impact on frozen ground, and thus frozen ground very nearly always acts as a near impervious area. Improved flood forecasting for urban catchments in cold regions can only be achieved with accurate modelling of urban winter runoff that involves the energy balance method, incorporating snow redistribution and urban snow‐cover characteristics, and using small time steps. Copyright © 2004 John Wiley & Sons, Ltd.

Estimating latent heat over a melting arctic snow cover

The latent heat flux over snow near Ny-Ålesund, Spitsbergen, was investigated for the 1999 snowmelt season to assess different methods of modelling the flux. Snow evaporation had hitherto been estimated as the residual of plot water balance calculations and was subject to measurement errors: hence a modelling solution was sought to make use of existing data. Precipitation, snow depth and albedo were measured daily. Runoff from the plots was recorded continuously. Wind speed, relative humidity and air temperature were measured at two levels (2 and 10 m) every 10 minutes; wind direction was noted hourly. Three models which simulate latent heat were assessed against evaporation and condensation measured by weighing several snow-filled containers each day. Two employ the bulk profile method (within the SNTHERM and CROCUS snowmelt models), while the third is the aerodynamic profile method (APM). Each follows the measured evaporation until snow-free patches develop after which the APM predicts evaporation whereas the snowmelt models predict condensation. The effect of wind is also noted. A major conclusion of this work is that the complexity of the land surface/atmosphere interactions, particularly when the snow cover breaks up, precludes the use of simple models for determining latent heat.

An Overview of the Field Experiment "Winter Mesoscale Convective Systems (MCSs) over the Japan Sea in 2001", and Comparisons of the Cold-air Outbreak Case (14 January) between Analysis and a Non-hydrostatic Cloud-resolving Model

A field experiment of snowfall systems, WMO-01, was conducted over the Japan Sea in the winter of 2001. During the WMO-01 period, cold-air outbreaks and passages of synoptic-scale cyclones were observed several times. By utilizing global analysis (GANAL) data, with a horizontal resolution of 1.25 degrees, the apparent heat source Q1, apparent moisture sink Q2, differential advection of moist static energy Dh, potential vorticity PV, sensible heat flux S and latent heat flux LvE were estimated to investigate characteristic features of weather over the Japan Sea. It is shown that the cold-air outbreak during 12 to 17 January was remarkable, where Q1, upper-level PV;S;LvE, and -Dh were the largest during the WMO-01 period. The cold-air was accompanied with the upper-level high PV anomaly, and the air-mass transformation took place strongly over the Japan Sea. The values of S + LvE reached approximately 600 Wm-2, and -Dh was large, indicating that the convective activity was strong. The heat and moisture budgets were compared with previous studies for the Japan Sea in winter. Generally speaking, it is shown that the budgets were similar to previous studies. Next, the 14 January case was examined in detail as a typical example of the cold-air outbreak. The convergence band (= JPCZ) was found extending southeastward from the east of joint of the Korean Peninsula to the San-in and Hokuriku areas. The L modes of convective clouds (parallel to the prevailing northwesterly wind) were seen on both sides of the JPCZ, and the T modes (normal to the NWly wind) were found on the northeastern side. A synoptic-scale cold trough was seen in eastern Asia at 500 hPa, and the polar jet was located on the southern side of the Japan Sea. Additional 1000 km-size PV anomalies slowly propagated eastward repeatedly along the northern side of the jet. This case was studied by using a non-hydrostatic cloud-resolving model with 5 km horizontal resolution (5 km-NHM). Characteristic features of the JPCZ were well reproduced. The 5 km-NHM outputs were also used to examine the heat and moisture budgets. Q*1 and Q*2 are defined similarly to Q1 and Q2, respectively, but the ice phase is included. Large differences from the GANAL analysis were found near the surface and above the height of 4 km. Near the surface, the evaporation of snow or rain may occur for the 5 km-NHM, while it may not for the analyzed Q1 and Q2 due to the vertically coarse data. The sensitivity experiments of cases with or without ice phase were also examined. It is found that the general features are similar in both cases, indicating that the ice phase is not very important for the diabatic process of clouds in this study.

The simulation of heat and water exchange in the boreal spruce forest by the land-surface model SWAP

All previous versions of a physically based land-surface model SWAP have assumed for simplicity that vegetation is fully covered by snow during the cold season. Such assumption is reasonable only for the regions dominated by short vegetation or for warm climates where snow processes are absent. The major goals of this paper are (i) modification of the latest version of SWAP by incorporation of tall vegetation into the cold-season parameterizations to make the model applicable for simulating heat and water transfer within a boreal forest biome and (ii) validation of the modified version using the data from a forested catchment located in the boreal zone. Modification of SWAP required to parameterize radiative and turbulent exchange between the forest crown and forest floor, partitioning snowfall between interception by the canopy (in doing so, snow interception differs from rain interception) and falling to the ground, formation of snow cover on the forest crown and forest floor including snow accumulation (both in solid and liquid fractions), snow evaporation, and snowmelt. The advanced model was validated using a set of hydrometeorological data measured during 18 years (1966–1983) at the Tayozhniy catchment (covered by boreal spruce forest), Valdai, Russia. Simulations of annual and monthly snow/rain interception, daily runoff at the catchment outlet, snow density, snow depth, snow water equivalent, soil water storage in three layers (0–20, 0–50 and 0–100 cm), and monthly evapotranspiration from the catchment were compared with observations. Analysis of the results of validation shows that the new version of the model SWAP reproduces the heat and water exchange processes occurring in mid-latitude boreal forest quite reasonable.

The role of aerodynamic roughness for runoff and snow evaporation in land-surface schemes—comparison of uncoupled and coupled simulations

This paper describes the impact of changes in aerodynamic roughness length for snow-covered surfaces in a land-surface scheme (LSS) on simulated runoff and evapotranspiration. The study was undertaken as the LSS in question produced widely divergent results in runoff, depending on whether it was used in uncoupled one-dimensional simulations forced by observations from the PILPS2e project, or in three-dimensional simulations coupled to an atmospheric model. The LSS was applied in two versions (LSS1 and LSS2) for both uncoupled and coupled simulations, where the only difference between the two versions was in the roughness length of latent heat used over snow-covered surfaces. The results show that feedback mechanisms in temperature and humidity in the coupled simulations were able to compensate for deficiencies in parameterizations and therefore, LSS1 and LSS2 yielded similar runoff results in this case. Since such feedback mechanisms are absent in uncoupled simulations, the two LSS versions produced very different runoff results in the uncoupled case. However, the magnitude of these feedback mechanisms is small compared to normal variability in temperature and humidity and cannot, by themselves, reveal any deficiencies in a parameterization. The conclusion we obtained is that the magnitude of the aerodynamic resistance is important to correctly simulate fluxes and runoff, but feedback mechanisms in a coupled model can partly compensate for errors.

Dynamics of the Martian Atmosphere–Soil–Polar Caps System

A numerical model of the Martian atmosphere–soil–polar caps system is constructed. We consider the conditions under which the seasonal meteorological variations in the system are stable. The fact that the planetary orbit is not circular is shown to be a sufficient condition for the appearance of a residual polar cap in the southern hemisphere if all parameters of the southern and northern hemispheres are identical. A latitudinal distribution of the atmospheric pressure is given for different seasons. A high-pressure region is shown to be formed at high latitudes of the planet. An altitude–latitude temperature distribution throughout the year is constructed. The snow accumulation and evaporation in the polar caps are examined. Seasonal features of the air mass dynamics are considered in terms of a two-dimensional atmospheric model.

Changes in wind regime around a nickel-copper smelter at Monchegorsk, northwestern Russia.

Wind stress may significantly change plant damage by aerial pollutants. However, almost no information exists on pollution-induced changes in wind regime around the strong emission sources. Wind speed, measured in industrial barrens adjacent to the nickel-copper smelter at Monchegorsk (Kola Peninsula, NW Russia), was two to three times as high as in the slightly polluted and nearly unpolluted forests. The ratio between the maximum wind velocity within 30 s and the average velocity of that time interval showed no temporal variation, thus characterising the wind regime. This ratio was highest in unpolluted forests, suggesting the predominance of gusty winds; in industrial barrens the maximum wind speed was only slightly higher than the average value. Since topography did not explain the spatial variation in wind regime, I conclude that my data represent the first direct evidence for distinct changes in wind regime caused by pollution-induced habitat deterioration. The results suggest that initial (partly pollution-induced) forest disturbance causes secondary effects (like increased snow evaporation, followed by soil freezing and plant damage) that may enhance further disturbance in a positive feedback fashion.

Impact of BOREAS on the ECMWF forecast model

This paper reviews the impact of the Boreal Ecosystem‐Atmosphere Study (BOREAS) on the development of a new land‐surface parameterization in the European Centre for Medium‐Range Weather Forecasts (ECMWF) global forecast system and discusses briefly the improvements that resulted in the model climate at high latitudes. We show how a long time series at a representative site was used to validate the model parameterizations of observed physical processes on both diurnal and seasonal timescales. As a direct result of BOREAS, the representation of several surface processes was greatly improved over the boreal forest. The introduction of separate tiles for tall and short vegetation meant that the boreal forest could be represented with some realism. In winter the albedo with snow under the trees was greatly reduced, and the introduction of a prognostic snow model with its own energy balance under the canopy meant that evaporation of snow in winter and spring was similarly reduced. An improved separate handling of liquid and frozen soil water meant that evaporation of frozen soil water is shut off, and surface runoff occurs when snow melts on frozen ground. Trees in the model now have larger more realistic unstressed vegetative resistance, as well as a stress factor for vapor pressure deficit, in addition to one for low light levels; both of which reduce summer transpiration to the lower levels observed over the boreal forest. The model does not yet have a global soil distribution, which means that it does not represent the organic soils that are characteristic of the black spruce sites, which have a larger water storage.

Conditional symmetric instability, frontogenetic forcing and rain‐band organization

AbstractThe mesoscale organization and the thermodynamic structures of cloud bands and rain bands observed on 9 January 1988 during the seventh Intensive Observation Period of the European field experiment project FRONTS 87 are investigated using both radiosounding measurements and dual Doppler‐radar data.The combined role of the conditional symmetric instability (CSI) and of the frontogenetic forcing in this banded organization is quantitatively assessed. It is shown that the observations are in agreement with the subsequent scenario, cloud bands initiated by the large‐scale forcing in the presence of a weakly CSI unstable atmosphere evolve rapidly into CSI rolls. The detailed thermodynamics within one of these rain bands is shown to be in very good agreement with the ones predicted by the CSI theory. A different dynamic behaviour between the cloud bands and the rain bands is, however, shown. Some additional role is suspected to be played by microphysics processes, in particular by snow evaporation, in the reinforcement of CSI ascending motions.

Snowpack changes around a nickel–copper smelter at Monchegorsk, northwestern Russia

Snow depth in industrial barrens adjacent to the nickel–copper smelter at Monchegorsk (Kola peninsula, northwestern Russia) by the end of the winter was reduced to one-third of the depth observed in weakened and healthy forests located 30–65 km from the smelter; this reduction was due to both decline (by one-half) in the amount (mass) of snow and increase in snow density. Since winter precipitation in Monchegorsk was about the same as in an unpolluted locality 56 km south-southwest of the smelter, and snowpack characteristics correlated with site-specific wind speed, the low amount of snow around the smelter is presumably due to snow movement from open windy habitats and enhanced snow evaporation during the wind transport; higher snow densities may be explained by wind-induced compaction of snow particles. Pollution affects snowpack characteristics by modifying wind regime via forest damage; in turn, decline in snow depth influence the growth form and (possibly) performance of trees that managed to survive in heavily polluted habitats. Thus, initial (partially pollution-induced) forest disturbance, through secondary effects, may enhance further disturbance in a positive feedback fashion; therefore, possible ecological effects of pollution-related snowpack changes should be accounted for in field studies conducted along pollution gradients within the forest zone.

Snow interception evaporation. Review of measurementtechniques, processes, and models

A global warming, primarily affecting wintertime conditions at high latitudes will influence the functioning of the boreal forest. The least known term of the winter water-balance equation is evaporation of snow intercepted in forest canopies. Several investigations stress the importance of snow-interception evaporation in coniferous forests and evaporation fractions of gross precipitation as large as 0.2–0.5 have been observed by investigators in Scotland, Canada, and Japan. Evaporation rates as high as 0.56 mm h−1 are reported. The largest differences between the rain and snow interception evaporation processes are the differences in storage. Snow storage (both mass and duration) is often an order of magnitude larger than that for rain. Snow interception changes the canopy albedo although some studies indicate the opposite. Process knowledge is limited because of measurement difficulties but it is known that canopy closure, aerodynamic resistance (r a ), and vapour-pressure deficit are important factors. Existing formulations of r a as function of storage location and age cannot fully explain observed differences in evaporation rates. Operationalhydrology and weather models, and GCMs describe snow interception in a very simplified way and might benefit from incorporation of more realistic schemes.

Hydrological Budgets and Surface Energy Balance of Seven Subbasins of the Mackenzie River from the ECMWF Model

Abstract The liquid and frozen hydrological budgets and the surface energy budget from seven subbasins of the Mackenzie River are analyzed using hourly integrals from the operational European Centre for Medium-Range Forecasts model from September 1996 to August 1998. The model budgets give estimates of precipitation (rainfall and snowfall), surface evaporation (of water and snow), runoff, and melt terms in the spring. On a basin scale and monthly timescale, the model precipitation correlates well with observations but has a 40% positive bias. On an annual basis, evaporation has a 60% positive bias. Although the annual runoff for the Mackenzie as a whole is close to the annual stream flow, this condition is not true for the subbasins. In the liquid water budget, nudging of soil water compensates for basin errors in runoff. The model snow budget is not closed because each new snow analysis depends heavily on climatological means. The surface energy balance on the basin scale also is analyzed. Although the m...

Carbon-water-energy relations for selected river basins

A biophysical process-based model was run using satellite, assimilated and ancillary data for four years (1987-1990) to calculate components of total evaporation (transpiration, interception, soil and snow evaporation), net radiation, absorbed photosynthetically active radiation and net primary productivity over the global land surface. Satellite observations provided fractional vegetation cover, solar and photosynthetically active radiation incident of the surface, surface albedo, fractional cloud cover, air temperature and vapor pressure. The friction velocity and surface air pressure are obtained from a four dimensional data assimilation results, while precipitation is either only surface observations or a blended product of surface and satellite observations. All surface and satellite data are monthly mean values; precipitation has been disaggregated into daily values. All biophysical parameters of the model are prescribed according to published records. From these global land surface calculations results for river basins are derived using digital templates of basin boundaries. Comparisons with field observations (micrometeorologic, catchment water balance, biomass production) and atmospheric water budget analysis for monthly evaporation from six river basins have been done to assess errors in the calculations. Comparisons are also made with previous estimates of zonal variations of evaporation and net primary productivity. Efficiencies of transpiration, total evaporation and radiation use, and evaporative fraction for selected river basins will be presented.

Simulating Climate Change Effects in a Minnesota Agricultural Watershed

AbstractThe effect of climate change on quality and quantity of runoff from a northern, agricultural watershed was simulated using the Soil and Water Assessment Tool, 1996 Version (SWAT96). SWAT's snow evaporation submodel was modified. SWAT was calibrated using water quality and quantity data measured in the Cottonwood River near New Ulm, MN (drainage area: 3400 km2). The standard errors after calibration were 3.31 mm, 157 kg/d, 752 kg/d, 3744 kg/d, and 85 t/d for mean monthly streamfiow, P yield, ammonia (NH3)/organic N yield, nitrate (NO3) yield, and sediment yield, respectively. The standard error for monthly streamflow was 9.62 mm. SWAT96 was then used to simulate the effect on the Cottonwood River watershed of a 2xCO2 climate scenario, obtained from the Canadian Climate Center's global circulation model. Assuming land cover and land management remained constant, SWAT96 projected a decrease in mean annual streamflow, P yield, NH3/organic N yield, NO3/nitrite (NO2) yield, and sediment yield. Mean monthly values changed significantly for many months of the year under the 2xCO2 climate scenario. The standard errors in SWAT's baseline simulations, however, were too high for the simulated climate change effects to be measurable for NO3/NO2 and sediment yields. The model assumptions and calibration methods used to obtain the accuracy required for simulating the effects of climate change lead to the conclusions that land use/land cover and land management practices are likely to have a greater impact on water quality than climate change and that SWAT must be calibrated to be used for climate change analysis.

The evaporation of precipitation and its geographical distribution

In order to estimate the evaporation of precipitation in different climate regions, as a first attempt, climate data from four meteorological stations have been used for mean daily precipitation, mean seasonal surface temperature and surface humidity and combined with mean seasonal vertical temperature profiles. Since the profiles are not representative for days with precipitation the results are preliminary and have to be interpreted with some caution. Nevertheless the following conclusions seem to be justified. The least evaporation - as well in absolute as in relative terms compared to the amount of precipitation produced in clouds - takes place in the humid tropics, where high humidity and low clouds prevail and also the most intense daily rain rate at the ground is observed. The calculations indicate that here the highest production of annual precipitation takes place above the cloud base. Evaporation of rain is limited to the levels just above the ground. The highest mean rain rate at the cloud base, however, seems to occur in the subtropics, where storms are rare but intense. Very dry environmental low-level air is responsible for the greatest average height of the cloud base and the most intense evaporation rate, which takes place at the highest possible level halfway between cloud base and ground. The high mean rain intensity computed at the cloud base is drastically reduced by evaporation, thus the observed mean daily rain rate on the ground ranks only on second place. In the midlatitudes precipitation is almost as frequent as in the tropics but the rates are lower, therefore the total annual observed precipitation is also much lower but still ranks on second place. The precipitation rate at the cloud base and the average cloud level do not indicate a great seasonal variation. The total annual precipitation produced in clouds is found to rank on the last place, with about 50% more rain being produced in the summer than snow in the winter, as also the number of days with precipitation is somewhat more frequent in the summer. The results suggest that probably about 60% or more of the precipitation produced in clouds also arrives at the ground. In contrast to the midlatitudes the subarctic shows a significant seasonal variation. Here the greatest number of days with precipitation is observed. The highest frequency of precipitation occurs during winter, when frequent cyclonic activity causes long lasting continuous precipitation. Both seasons contribute about equal amounts to the total annual precipitation, despite the longer duration of the winter season, as the summerly rain rate at the ground exceeds the intensity of snow falls. At the cloud base, however, the precipitation on a winter day seems to exceed the daily production of rain in the summer by almost 100%. Our results suggest a significant difference in the height of the cloud base between summer and winter. During the winter season the cloud base is found at a rather high level. The humidity profile, which should be fairly reliable because of the high frequency of days with precipitation, indicates a high reaching moist but unsaturated layer in which considerable evaporation of snow seems to take place. Actually this result was expected and it is suggested that in arctic and subarctic regions the reduction of precipitation due to evaporation in the subcloud layer is substantial, at least in a relative sense, as during winter the fraction of precipitation generated in clouds, which evaporates, is comparable with the evaporation of rain in the subtropics. As a consequence in the subarctic probably not much less precipitation is produced in clouds than in the tropics, with more than three times as much snow leaving the cloud base as rain, mainly because of prevailing cyclonic conditions during winter time.

Snow Distribution and Melt in Central Tien Shan, Susamir Valley

Using data collected on expeditions and long-term records, evaluations of snow accumulation and melt in high-altitude catchments, typical of much of the central Tien Shan, are presented. Over areas of about 500 km2, the main factor influencing spatial distribution of precipitation and snow is elevation. Maximum snow water equivalent, dates of maximum accumulation, and the duration of snow cover plot as a parabolic function of altitude. Over areas larger than 500 km2, the effects of rain shadow are strengthened in the cold season and precipitation decreases in eastern direction. However, during the warm season, the main predictor of precipitation and snow distribution is elevation. In areas less than 500 km2, exposure has a significant influence on snow redistribution. However, there is a similarity in snow distribution in spite of differences in elevations or the angle of inclination of slopes. Highest correlation length in snow accumulation occurred at a 50 to 60 km horizontal distance and up to 1.0 km in altitude. Solar radiation contributed 74% of energy for snowmelt and evaporation, and turbulent heat contributed 26% during expeditionary observations in May 1992. Average daily snow evaporation used 10% of available energy while snowmelt used 90%.

Snow Distribution and Melt in Central Tien Shan, Susamir Valley

Using data collected on expeditions and long-term records, evaluations of snow accumulation and melt in high-altitude catchments, typical of much of the central Tien Shan, are presented. Over areas of about 500 km2, the main factor influencing spatial distribution of precipitation and snow is elevation. Maximum snow water equivalent, dates of maximum accumulation, and the duration of snow cover plot as a parabolic function of altitude. Over areas larger than 500 km2, the effects of rain shadow are strengthened in the cold season and precipitation decreases in eastern direction. However, during the warm season, the main predictor of precipitation and snow distribution is elevation. In areas less than 500 km2, exposure has a significant influence on snow redistribution. However, there is a similarity in snow distribution in spite of differences in elevations or the angle of inclination of slopes. Highest correlation length in snow accumulation occurred at a 50 to 60 km horizontal distance and up to 1.0 km in altitude. Solar radiation contributed 74% of energy for snowmelt and evaporation, and turbulent heat contributed 26% during expeditionary observations in May 1992. Average daily snow evaporation used 10% of available energy while snowmelt used 90%.

Evaporation of Snow Intercepted by a Todo-fir Forest (I) Water Balance Easurements

"Evaporation of Snow Intercepted by a Todo-fir Forest (I) Water Balance Easurements." Journal of Forest Research, 2(1), p. 67

SNOWPACK CHANGES RESULTING FROM TIMBER HARVEST INTERCEPTION, REDISTRIBUTION, AND EVAPORATION1

ABSTRACT: Three processes were examined as causing snowpack changes in forest clearings. Two of the three contribute to increases and one counteracts by reducing snowpack. The two that increase snowpack are redistribution and decreased loss to interception. Snow evaporation from a clearing counteracts snowpack increases. Research has indicated that as vegetation density increases, so too does the loss to interception. As snow in the canopy reaches the limit that the canopy can hold (the threshold amount) evaporation increases. Aerodynamics of the forest canopy were studied as well. As timber is cut, wind patterns are disturbed, creating disruptions in the wind velocity gradient depositing snow in openings. This redistribution leads to an increased snow water equivalent and augments runoff. Snow evaporation was shown to increase proportionally with opening size. Evaporation offsets the water yield gains derived from forest cut. It was found that this offset is inclusive to the measurements of water yield changes in experimental forests. An optimal size of harvest block may be five tree heights in width as suggested by numerous studies.

トドマツ林における降雪の遮断蒸発量(II) : 熱収支モデルによる推定と水収支的観測との比較

トドマツ林における降雪の遮断蒸発量(II) : 熱収支モデルによる推定と水収支的観測との比較