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start:hype_model_description:processes_above_ground [2019/09/20 12:50]
cpers [Alternative potential evaporation models]
start:hype_model_description:processes_above_ground [2020/04/30 10:56] (current)
cpers [Table]
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 Where <​m>​{Delta}h</​m>​ is a class'​s elevation deviation from the subbasin average elevation and //snfrac// is the average fraction of precipitation that falls as snow calculated from subbasin temperature (<​m>​T_i</​m>​) and temperature thresholds (see equation below), or from input. Where <​m>​{Delta}h</​m>​ is a class'​s elevation deviation from the subbasin average elevation and //snfrac// is the average fraction of precipitation that falls as snow calculated from subbasin temperature (<​m>​T_i</​m>​) and temperature thresholds (see equation below), or from input.
-==== Rainfall and snowfall ​calculation ​==== +==== Rainfall and snowfall ​separation ​==== 
-The rain/snow fraction of precipitation is calculated based on temperature or given as an input time series. Different temperatures can be used in the equation, i.e. basin average or class temperature. When the air temperature (//T//) is around the threshold temperature for mixed precipitation (land-use dependent parameter //ttmp// plus general parameter //ttpd//) both rain and snow. The interval for mixed precipitation is given by the parameter //ttpi//. For temperature below threshold minus //ttpi//, the precipitation is assumed to be in solid form only and is added to the snowpack. If the air temperature is greater than the threshold temperature plus //ttpi//, the precipitation is assumed to be solely in liquid form. For intermediate temperatures,​ the precipitation is assumed to be a mixture of liquid and solid forms i.e. as both rain and snow. The proportion (<​m>​a_rain</​m>​) of precipitation ​(//​P//​) ​that falls as rain depends linearly on the temperature. ​+The rain/snow fraction of precipitation is calculated based on temperature or given as an input time series. Different temperatures can be used in the equation, i.e. basin average or class temperature. When the air temperature (//T//) is around the threshold temperature for mixed precipitation (land-use dependent parameter //ttmp// plus general parameter //ttpd//) both rain and snow. The interval for mixed precipitation is given by the parameter //ttpi//. For temperature below threshold minus //ttpi//, the precipitation is assumed to be in solid form only and is added to the snowpack. If the air temperature is greater than the threshold temperature plus //ttpi//, the precipitation is assumed to be solely in liquid form. For intermediate temperatures,​ the precipitation is assumed to be a mixture of liquid and solid forms i.e. as both rain and snow. The proportion (<​m>​a_rain</​m>​) of precipitation that falls as rain depends linearly on the temperature. ​
  
  
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 <m> a_{rain}=1-sffrac </m> <m> a_{rain}=1-sffrac </m>
  
-The amount of rainfall and snowfall is calculated from the corrected precipitation.+The amount of rainfall and snowfall is calculated from the corrected precipitation ​(//P//).
  
-<m> rainfall=prec*a_{rain} </​m>​ +<m> rainfall=P*a_{rain} </​m>​ 
-<m> snowfall=prec*(1-a_{rain} ) </m>+<m> snowfall=P*(1-a_{rain} ) </m>
  
 +==== Snowfall distribution ====
 +
 +The optional snowfall distribution models redistribute the snowfall of a catchment among the classes depending on wind. The model uses Winstral coefficients. For each subbasin and class and wind direction a Winstral coefficient (//WSF//) is given as input data to the model. Wind direction is calculated from forcingdata of westerly (U) and southerly (V) wind. The wind direction is translated to the closest quadrant or octant, and the Winstral coefficient of that direction is used.
 +
 +The Winstral coefficient is, with some scaling parameters, used to calculate the relative snowfall for each class this time step. There are two models; one that use a linear function (ref Gustafsson et al, 2015) and one that is log-linear (ref Clemenzi et al., 2020). ​
 +
 +<m> relative_snowfall = 1. + WSFscale *WSFluse * (WSF + WSFbias) </​m> ​
 +
 +<m> relative_snowfall = 10 ^ (WSFscale * WSFluse * (WSF + WSFbias)) </​m> ​
 +
 +//​WSFscale//​ and //WSFbias// are general parameter, //WSFluse// is a scaling parameter depending on land-use. The relative snowfall is limited to the interval [1 - //sfdmax//, 1 + //sfdmax//] for the linear model and [0,//​sfdmax//​] for the log-linear. //sfdmax// is a general parameter. The relative snowfall is normalized within each subbasin so that the subbasin mean snowfall is preserved. The snowfall distribution is applied only if snow is falling for a fraction of the subbasin area that is larger than a limit (//​limit//​).
 +
 +NOTE: The snowfall distribution model only works for simulation of the winter period.
  
  
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 |Rainfall and snowfall calculations| |//ttmp, ttpd, ttpi//​|[[start:​hype_file_reference:​par.txt|par.txt]]| |Rainfall and snowfall calculations| |//ttmp, ttpd, ttpi//​|[[start:​hype_file_reference:​par.txt|par.txt]]|
 |:::​|//​sffrac//​| |[[start:​hype_file_reference:​sfobs.txt|SFobs.txt]]| |:::​|//​sffrac//​| |[[start:​hype_file_reference:​sfobs.txt|SFobs.txt]]|
 +|Snowfall distribution|U,​ V | |[[start:​hype_file_reference:​uwobs.txt|UWobs.txt]],​ [[start:​hype_file_reference:​vwobs.txt|VWobs.txt]]|
 +|:::​|//​WSF//​|//​wsf_nn_d//​ |[[start:​hype_file_reference:​geodata.txt|GeoData.txt]]|
 +|:::| |//​WSFscale,​WSFluse,​WSFbias,​sfdmax//​ |[[start:​hype_file_reference:​par.txt|par.txt]]|
 +|:::​|//​limit//​ |//sfdlim// |:::|
  
  
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 | ::: | calculate_subbasin_precipitation | | ::: | calculate_subbasin_precipitation |
 | ::: | set_atmospheric_parameters_corrections | | ::: | set_atmospheric_parameters_corrections |
 +| ::: | calculate_winddirspeed |
 +| ::: | calculate_snowfall_distribution |
  
 ===== Evaporation ===== ===== Evaporation =====
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 The actual evaporation may also depend on soil temperature (//​soiltemp//​). It is then reduced for temperatures above land use parameter //ttrig// and depend on two other land use parameters (//tredA//, //tredB//) as well (Figure 3).  The actual evaporation may also depend on soil temperature (//​soiltemp//​). It is then reduced for temperatures above land use parameter //ttrig// and depend on two other land use parameters (//tredA//, //tredB//) as well (Figure 3). 
  
-|{{:​start:​hype_model_description:​pet_soiltemp.png?​400|}}| +| {{:​start:​hype_model_description:​pet_soiltemp.png?​400}} ​                                                                                   
-|Figure 3 Soil temperature factor for reduction of soil evapotranspiration. Parameter values: //​ttrip//​=1,​ //​tredA//​=0.5,​ //​tredB//​=1.|+| Figure 3 Soil temperature factor for reduction of soil evapotranspiration. ​\\ Parameter values: //​ttrip//​=1,​ //​tredA//​=0.5,​ //​tredB//​=1. ​ |
  
 The soil temperature evapotranspiration reduction is calculated as: The soil temperature evapotranspiration reduction is calculated as:
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 <m> evapp = evapp*factor </m> <m> evapp = evapp*factor </m>
  
-The actual soil evaporation is set to zero for temperatures below the threshold temperature and for negative potential evaporation estimates (condensation).+The actual soil evaporation is set to zero for temperatures below the threshold temperature and for negative potential evaporation estimates (condensation). It may also be affected by frozen soil model, which then limit evaporation to the liquid part of soil water.
  
-A river with an area (i.e. is a class), flooded floodplains and lakes are assumed to evaporate at the potential rate, when the air temperature is above the threshold temperature (//ttmp//). Evaporation is limited by the water body's volume.+A river with an area (i.e. has a class), flooded floodplains and lakes are assumed to evaporate at the potential rate, when the air temperature is above the threshold temperature (//ttmp//). Evaporation is limited by the water body's volume.
  
  
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 Nitrogen dry deposition on water surfaces is specified in GeoData.txt for each subbasin, while dry deposition of phosphorus is specified by a model parameter //​drydepPP//​ (land use dependent). ​ Nitrogen dry deposition on water surfaces is specified in GeoData.txt for each subbasin, while dry deposition of phosphorus is specified by a model parameter //​drydepPP//​ (land use dependent). ​
  
-For both nitrogen and phosphorus wet deposition is added through the concentration of precipitation (as described above), while for dry deposition an amount of the nutrient is added to the river (if it has a class-area) or lake water. If the lake is divided atmospheric deposition are added to the fast lake part (FLP).+For both nitrogen and phosphorus wet deposition is added through the concentration of precipitation (as described above), while for dry deposition an amount of the nutrient is added to the river (if it has a class-area) or lake water.
  
 Alternatively wet deposition of phosphorus on water surfaces can be specified by a general model parameter (//​wetdepspl//​) as a load. Monthly load of IN atmosperic depostion on water surfaces can be specified in GeoData.txt for each subbasin. Alternatively wet deposition of phosphorus on water surfaces can be specified by a general model parameter (//​wetdepspl//​) as a load. Monthly load of IN atmosperic depostion on water surfaces can be specified in GeoData.txt for each subbasin.
start/hype_model_description/processes_above_ground.1568976638.txt.gz · Last modified: 2019/09/20 12:50 by cpers