RainfallRunoff Model: parameters
The rainfallrunoff model is a dynamic (daily) lumped (semidistributed)
water budget model for small to mediumsized basins.
The model parameters are grouped into three sets:
 Basin parameters
 Model parameters
 Basin specific constants
Of these three sets, the model parameters can be used for calibration, for
which an automatic calibration routine
based on a constraint satisficing approach is implemented as an efficient MonteCarlo scheme,
is also available;
basin characteristics, within the limits of conceptual uncertainty are supposed to be constant;
the site specific model constants may vary from location to location,
but are again assumed to be constant
at least between scenarios for one and the same basin.
Basin Parameters:
These describe the primary physical properties of the basin;
a special case is the orography (area/elevation distribution) that is defined with a specific editor.
Basin parameters should be inherited from a corresponding river basin object (not yet implemented)
describing such physical (as opposed to model scenario) entities.
Basin Parameters 
Basin Size  km² 
Overall size of the hydrographic catchment or basin to be modeled;
please note that this only used for consistency checking,
the actual area used for computations id derived from the
area/elevation distribution. 
Minimum Elevation  masl 
Elevation of the lowest point (the outflow) of the basin;
used for consistency checking, and to estimate average gradients. 
Maximum Elevation  msal 
Elevation of the highest point in the catchment;
the altitude range (as defined by the area/elevation editor) is used
to correct vertical temperature distribution and account for the
distribution of snow accumulation and snow melt 
Basin Length  km 
Approximate basin length (maximum dimension along the main direction of the river) 
Main Channel Length  km 
Approximate length of the main (first order) river channel; used for routing 
Drainage Length  km 
the total length of all perennial channels; for basins with only intermittent,
seasonal flow, use the total length of all significant channels that contribute to runoff;
used to determine the average travel distance of the interflow 
Average Channel Width  m 
an approximate measure (due to possibly large seasonal variation),
representing average (surface) width, possibly approximated by the
dimension 1/3 upstream from the river mouth or confluence; used to estimate routing parameters 
Channel type  symbolic 
selection of channel types (symbolic) with associated roughness parameters for the routing 
Land use/land cover a class residual (other) is constructed as the difference to make up 100% 
Forest  % 
area and fraction of the area covered by forest 
Agriculture  % 
area and fraction of the area covered by agricultural fields,
including both rain fed and irrigated agriculture 
Meadows  % 
area and fraction of the area covered by meadows, uncultivated 
Model parameters are the primary candidates for calibration;
they express the specific properties of a basin, as interpreted and used by the model.
Model Parameters
 Precipitation Factor  % per 100m  precipitation is assumed
to change (usually increase) with elevation; the parameter describes the relative increase
with every 100 m layer 
Precipitation Scaling  
used to adjust the precipitation input which is assumed to represent values characteristic
for the lower end of the basin (see above) 
Lapse Rate  deg/100m 
The adiabatic lapse rate describes the decrease of temperature with elevation,
usually in the order of up to one degree Centigrade per 100 m 
Temperature Shift  deg 
ad additive shift used to adjust the temperature input to be representative of the
lower end of the basin, see above 
Field Capacity  mm/m 
soil water holding capacity, average, of the soil system;
this will be corrected by the rootzone thickness of the individual land use classes to obtain a
basin wide (weighted) average 
Maximum Percolation  mm/day 
maximum speed of percolation from the unsaturated zone (virtual drainage store)
to the shallow groundwater 
Routing parameters, control segment outflow 
Delay, Interflow   
weight factor, defines the relative weight of inflow into a "hydraulic segment" 
Delay, Surface   
weight factor, defines the relative weight of inflow into a "hydraulic segment" 
Delay, Channel   
weight factor, defines the relative weight of inflow into a "hydraulic segment" 
Storage, Interflow   
weight factor, defines the relative weight of content of a "hydraulic segment" 
Storage, Surface   
weight factor, defines the relative weight of content of a "hydraulic segment" 
Storage, Channel   
weight factor, defines the relative weight of content of a "hydraulic segment" 
Initial Conditions (to be simplified as: very wet  wet  normal  dry  very dry) 
Snowpack  mm 
initial water content of the snow pack at the begin of the simulation. Please note that
this is expressed in mm water equivalent and assumed to be geometrically distributed,
with 50% in the topmost layer, 25% in the second from the top, etc. 
Interception Storage  mm 
if the simulation is started on or immediately after a rainy day,
interception storage could be full, i.e., all surfaces are wet. 
Soil Moisture  % 
specified as a % of field capacity depending on the season and the weather at or immediately before
the start of the simulation, soils can contain more or less moisture 
to minimize dependency on initial conditions, starting the simulation in a dry period is advisable. 
Groundwater (shallow, GWS)  mm 
initial water content of the shallow groundwater system  the groundwater
is represented as a nonlinear reservoir, contributing base flow as a function of
its content or level. 
Groundwater (deep, GWD)  mm 
initial water content of the deep groundwater system  the groundwater
is represented as a nonlinear reservoir, contributing base flow as a function of
its content or level. 
Groundwater parameters 
Deep Percolation  mm/m/day 
percolation from the shallow to the deep aquifer 
Response Coefficient (shallow)  
multiplier a in baseflow = a * GW ** b 
Response Exponent (shallow)  
exponent b in baseflow = a * GW ** b 
Response Lag (deep)  days 
describes the (half) time it would take to drain (half)
the deeper groundwater reservoir, by contributing to the baseflow 
Model Constants
These are considered constants, but may need adjustment for different climatic zones,
of basins of very different type (urban, alpine, wadis, etc).
Basin specific Model Constants
 deg/day evaporation  mm/deg 
evapotranspiration is estimates with a simple degree day factor, that describes how
many mm of water will evaporate for each degree of average air temperature; applies to
interception storage 
deg/day snowmelt  mm/deg 
snowmelt is described similar to evapotranspiration: for every degree average air temperature,
a certain amount of snow (in mm) is melted and added to the runoff 
heavy rain limit  mm 
this threshold defines conditions of heavy rain and associated high levels
of humidity, that affect (reduce) evaporation 
evpt reduction factor for heavy rain  
under conditions of heavy rain (defined above) and high (saturated) relative humidity,
evaporation will slow down. 
reduction factor infiltration  
under conditions of heavy rain and very wet (saturated) soils, infiltration
speed can be reduced due to the swelling of soil particles. 
reduction factor percolation  
under conditions of heavy rain and very wet (saturated) soils, infiltration
speed can be reduced due to the swelling of soil particles. 
evtp temperature threshold  deg 
evapotranspiration is a nonlinear function of temperature; at very low
temperatures, physiological water demand will slow down. 
warm rain coefficient snowmelt  mm/mm*deg 
snow melt is primarily driven by air temperature; however, rain falling on snow
will also contribute to snow melt due to the high heat capacity of the (warm) rain water; assuming
that the temperature of the rain is close to air temperature, rain will effectively
increase the degree day factor that describes the effect of temperature only. 
Landuse specific constants (one set for each land cover class including residual) 
average rootzone  m 
rootzone thickness defines the vertical extent of the zone for effective
infiltration, water holding in the soils, as well as evapotranspiration 
deg/day coefficient evpt  mm/deg 
evapotranspiration is estimates with a simple degree day factor, that describes how
many mm of water will evaporate for each degree of average air temperature 
Interception storage capacity  mm 
before precipitation reaches the ground, it first is intercepted by land cover:
this constant defines the land use specific amount 
maximum infiltration  mm/day 
the maximum amount of infiltration (during a day) depends on the land cover and
thus porosity of the ground, soil, root zone thickness, soil moisture, etc. 
