4. Hydrograph model
The Hydrograph model is a distributed process-based hydrological
modelling system (Vinogradov et al., 2011). It describes all components
of the land hydrological cycle, including precipitation and its
interception; snow accumulation and melting; evaporation from snow,
soil, and vegetation cover; surface flow and infiltration; soil water
dynamics and flow; heat dynamics and phase change in soil layers;
underground flow formation, slope and channel flow transformation. The
model requires the following atmospheric variables as its input: air
temperature and humidity, the amount of precipitation. The output are
flow hydrographs, water balance and state variables of basin elements.
The model can be run at time steps from minutes and hours to daily.
The concept of runoff elements used in the Hydrograph model for spatial
discretization of basins is a key concept. The catchment area consists
of runoff elements of different levels – surface, soil and underground.
The concept proposes the system of runoff elements characteristics, such
as outflow time which include the time and intensity of outflow from
elements, depending on the water storage (Vinogradov et al., 2011).
Within the discretization procedure, the basin territory is divided into
several conditionally homogeneous parts called runoff formation
complexes (RFC). It is assumed that the characteristics of soil,
vegetation, topography, and other components of the landscape are
constant within each RFC, while the runoff formation process is uniform.
The main parameters of the model are the physical properties of the
landscapes that may be observed in nature and are classified according
to the types of soil (specific weight, specific heat capacity of soil
particles, specific heat conductivity of dry soil particles, porosity,
maximum water holding capacity, wilting point, ice impedance factor,
infiltration coefficient, hydraulic parameter of subsurface system of
runoff elements), vegetation (seasonal shadiness by vegetation cover,
landscape albedo, interception storage capacity, coefficient of
evaporation from the interception storage during the maximum development
of vegetation cover, parameter of heat supply from atmosphere to soil
surface, phenological dates) and other characteristics (Vinogradov et
al., 2011; Semenov et al., 2013).
The method for simulating thermal dynamics in the upper layer of ground
is incorporated in the Hydrograph model. It is based on several
techniques that simplify the differential equation of thermal
conductivity in the soil profile and allows bringing the system of
differential equations to a system of linear algebraic equations without
losing the quality of the simulation results (Lebedeva et al., 2015;
Semenova et al., 2015).
The Hydrograph model has been successfully applied to simulate the river
runoff formation in cold regions with a lack of ground-based observation
data (Semenova et al., 2013; Semenova et al., 2015; Vinogradov et al.,
2011). Here we present the results of parameterization and verification
of the Hydrograph model for mountainous landscapes of the North-East of
Russia based on the data of short-term special observations. For
modeling, the Suntar River basin is presented as a hexagonal grid, with
32 representative points (RP) (Fig. 1). Each RP has its own set of point
characteristics, which include the coordinates, latitude, elevation,
slope aspect, slope inclination and lag time.