Below you can find also the audio (in Italian) of the lecture: Richards equation (21.9 Mb); Frozen Soil (18.4 Mb); Snow (7.1 Mb). I gave longer presentations on Richards equation, in Todini Symposium (here), and at the summer School on Landslide Modelling in Praia a Mare (here).
An update. A new treatment of part of this matter is given by Niccolo Tubini in his Master Thesis. The slides he used in the 2017 lecture are here.
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Casulli, V., and Zanolli, P., A Nested Newton-Type Algorithm for Finite Volume Methods Solving Richards' Equation in Mixed Form, SIAM J. Sci. Comput., 32(4), 2255–2273, Volume 32, Issue 4, 2010.
Cordano E., and Rigon R., A mass-conservative method for the integration of the two-dimensional groundwater (Boussinesq) equation, Water Resour. Res., 49, doi:10.1002/wrcr.20072, 2013.
Dall'Amico, Matteo (2011), Coupled Water and Heat Transfer in Permafrost Modeling. Ph.D. Thesis
Dall’Amico, M.; Endrizzi, S., Gruber, S; and Rigon, R. (2011), An energy-conserving model of freezing variably-saturated soil, The Cryosphere.
Endrizzi S., Gruber S., Dall’Amico M., Rigon R., GEOtop 2.0.: Simulating the combined energy and water balance at and below the land surface accounting for soil freezing, snow cover and terrain effects, Geosci. Model Dev., 2015