Climatology in shallow caves with negligible ventilation: Heat and mass transfer

The present numerical study investigates the effect of a cavity located at shallow depth below ground surface. The temperature field in the rock matrix surrounding the cave is significantly deformed compared to the case without cavity. Fluxes at cave wall, related to radiation, air-convection and evaporation/condensation (in case of a humid cave), all contribute to a significant homogenisation of wall temperatures. In case of high humidity, simulations of evaporation/condensation periods show that some parts of the wall may be durably (several months) subjected to significant condensation (or evaporation). Real meteorological data, i.e. 77 years of external temperature data of the Gourdon station in France, have been used as input of the model. Results of simulations have been compared to experimental temperature of Lascaux cave, with good agreement considering some simplifying hypotheses assumed for this modeling. The asset of such a model is the low computing time required to simulate several years, and thus its ability to follow long time evolution. Results significantly improve our understanding of conditions taking place in a shallow cavity, what will help improving the management of caves, especially those with very fragile decorations such as Paleolithic paintings. The model may help to identify areas which are the most exposed to weathering and to test the effect of past and potential changes in nearby conditions. It may also be useful for managing shallow underground constructions (e.g. a mine or even a cellar).