Ilias has extensively worked with the PDM model since its simplicity allows robust parameter identification and generally improves the chances of successful regionalisation (Pechlivanidis et al., 2010).


Probability Distribution Moisture (PDM)

The Probability Distributed Moisture (PDM) model is a conceptual model, which uses a distribution of soil moisture storage capacities for soil moisture accounting and a number of linear or non-linear reservoirs for the routing component (Moore, 2007).

The soil moisture storage capacity is assumed to be described by a Pareto distribution and the effective rainfall is equal to the soil moisture excess calculated at each time step. The evaporation rate is assumed equal to the potential evaporation multiplied by the relative saturation of the catchment.

The effective rainfall is split into ‘‘quick” and ‘‘slow” pathways, which are generally routed via parallel storage components. The simulated streamflow is determined by the combination of the two pathways. The total streamflow is finally delayed to adjust the time to peak response.

An explicit channel routing module is introduced when moving from lumped to semi-distributed representation to route the flow from the subunit to the catchment outlet.

A parsimonious structure of the PDM model.


Moore, R.J., 2007. The PDM rainfall-runoff model. Hydrology and Earth System Sciences, 11(1): 483-499.

Pechlivanidis, I.G., McIntyre, N.R. and Wheater, H.S., 2010. Calibration of the semi-distributed PDM rainfall-runoff model in the Upper Lee catchment, UK. Journal of Hydrology, 386(1-4): 198-209.