Abstract
Rain waters from three regions of South Arabia were analyzed for 18O/16O and D/H. Appreciably enriched isotopic compositions were found from every region. The evaporation effect on the rain drops was not found to be major cause because the rains are plotted considerably in parallel with the Craig's meteoric water line. The parallelism prevails up to certain enriched level usually exceeding SMOW in δ18O vs. δD diagram. Instead the causes of the isotopic enrichment were ascribed to the large difference in evaporation and condensation temperature and/or to the proximity between vapor forming sea area and the high mountains, i.e., the most probable area for rain formation under the forced air lifting in arid region. The depletion of heavy isotopes in the deep-born groundwater of old age indicates a different climate system to have prevailed in the past. Should “Global Warming” proceed, the intensified south-west Indian monsoon in summer may create isotopically enriched terrestrial waters in dominance.
