GEOtop 2.0 was mainly the work of Stefano Endrizzi, with the help of many actually: but he recoded most of it with great attention to the infinite details.
Here excerpts from the introduction:
"... There is a great diversity of models (understood here as mathematical representations of one or more processes) and simulators (computer programs, usually comprising imple- mentations of several models to represent a natural system) to simulate cold regions processes. GEOtop 2.0 (hereafter GEOtop) is a process based model which develops from the blueprint GEOtop 0.75 described in Rigon et al. (2006) and Bertoldi et al. (2006). It was built in the idea that the com- bination of terrain effects, energy and water balance pro- duce unique results for different meteorological forcings, which makes difficult the a priori exclusion of any of the processes. GEOtop covers the full spectrum of hydrological fluxes, but this paper mainly focuses on the aspects related to the cryosphere. In this context, permafrost research provides an intersections of phenomena related to frozen soil, the flow of water, and the snow pack. ...
Just a few models exist that try to cope with all of the com- plexities of modeling in a spatially distributed manner the full range of hydrological processes. Sophisticated process-based models are available, like CROCUS (Brun et al., 1992), CATHY (Paniconi and Putti, 1994), ALPINE3D (Lehning et al., 2006), HYDROGEOSPHERE (Therrien and Sudicky, 1996), CATFLOW (Zehe et al., 2001), IHMR (VanderKwaak and Loague, 2001), and SHETRAN (Abbott et al., 1986), but usually they cover either the cryosphere (with no care of water after melting) or the surface-subsurface fluxes in the above zero centigrades domain of temperatures. This choice makes it impossible to really understand complex environmental settings such as, for instance, the alpine type areas around the world, where snow and freezing soil significantly after the conditions of water fluxes in winter, and certainly affects hydrology and ecology also in spring, early summer, and late autumn (Barnett et al., 2005; Endrizzi and Marsh, 2010; Horton et al., 2006). In other models, like JULES (Best et al., 2011), VIC (Liang et al., 1994), tRIBS (Ivanov et al., 2004), JGRASS-NewAGE (Formetta et al., 2011), the whole system of interactions is accounted for, but the set of equations required for representing such environments are simplified with a priori parameterisations of some interaction of processes. ...
GEOtop 2.0. is significantly different from GEOtop 0.75. It includes a fully three-dimensional description of the Richards equation, whereas in the previous version the equa- tion was only solved in the vertical direction and the lateral flow was parameterised, in a similar way as in large-scale land surface models. In the new version, a multilayer snow cover and the surface energy balance are fully integrated in the heat equation for the soil, which is solved with a rigorous numerical method based on Kelley (2003), while in the previous version, snow cover was described with a bulk method (Zanotti et al., 2004) and the surface energy balance, though complete in its components and accommodating complex ter- rain, was not numerically coupled to the soil heat equation. In GEOtop 2.0, soil freezing and thawing are represented, meteorological forcings are distributed, and channel routing is described as overland flow with the shallow water equation neglecting the inertia. The description of vegetation with a double-layer surface scheme in order to more accurately represent the heat and vapour exchanges of vegetation with the soil surface and the atmosphere has also been included in GEOtop and described in Endrizzi and Marsh (2010). ... "
The final version of the paper has been accepted in September 2014. And can be found on-line at the GMD site.
From this version, the source code is available at Google code, https://github.com/skyglobe/geotop#, under GPL v. 3 license.
The main website of GEOtop is back at http://www.geotop.org