Monthly hydrological model GR2M

Monthly hydrological model GR2M

The last version of the GR2M model was developed by Mouelhi (2003).

The scheme of the GR2M model is presented below.

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Description of the GR2M model

In the GR2M model, the production function relies on a soil moisture store that is very similar to the one used in GR4J. Given a precipitation P, the level S in the store becomes S1 and is defined by:

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The parameter X1, the maximum capacity of the store, is positive and is given in mm.
La pluie P1 en excès est donnée par :
P1 = P + S – S1
Given the potential evapotranspiration E, the level S1 becomes S2: :

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The production store then empties with a percolation P2 and its level S, ready for the computations of the following month, given by:

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and

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The total precipitation P3 that reaches the routing store is given by:
P3 = P1 + P2
The level R in the routing store then becomes R1:
R1 = R + P3
A water exchange term is then calculated:
F = (X2 – 1).R1
The parameter X2 is positive and has no dimension. The level in the store becomes:
R2 = X2.R1
The store, with a fixed capacity equal to 60 mm, empties following a quadratic function.
The streamflow is given by:

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 The model has two parameters to optimise during its calibration:

  • X1 : the capacity of the production store (mm),
  • X2 : the exchange coefficient (-).

See also