[en] In this report results of tritium tagging experiments in the Thar Desert, Rajasthan, India are presented. They are compared with the results obtained at Ahmedabad, a region with about three times higher rainfall than the Thar Desert but still on the fringe of the desert in the semi-arid region of NW India. The moisture content of the soil in the Thar Desert is only about 2-6% as compared with 5-15% in Ahmedabad. The two models represent basic understanding of the evapotranspiration, run-off and soil moisture movement processes in the arid regions of Thar Desert. The studies indicate that even in a very low rainfall region the groundwater recharge can be quite substantial, amounting to about 7-15%