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Playa lakes occur in and and semi-arid climates and have a significant economic, ecological and cultural value. They are particularly vulnerable to changing hydrologic regimes due to climate change or human activities. We determined the hydrological regime of 10 playa lakes in southern Spain based on water budgets for a 5-year period (1997 2001). Surface runoff was measured in the watersheds, precipitation and evaporation/evapo-transpiration estimated using local meteorological data and ground-water flows assessed using a network of wells and piezometers. The examination of seasonal variations in the lakes’ water levels and the water budgets indicated that ground-water discharge plays a key role in the hydrological dynamics and the maintenance of the playa ecosystems. Major inorganic ions and stable hydrogen and oxygen isotopes in lake water, ground-water and springs were measured. Water samples from the lakes and ground-water were a mixture of cations -SO42-. and -Cl- type due to the aridity of the climate and lithologies of the basin. The high TDS (63.4 g/l) content of some ground-water samples indicates regional geologic control on water quality and the dissolution of gypsum and halite. Stable oxygen isotope ratios for lake water (-3.6 to 9.8 parts per thousand delta O-18(SMOW)) were different from those of ground-water and springs (-6.8 to 1.1 parts per thousand delta O-18(SMOW)) suggesting different evolutional patterns. The results of this study provides evidence that the combination of water budgets, hydrochemistry and stable isotope hydrology can lead to a better understanding of wet playa’s hydrology. This approach could, thus, prove helpful to establish hydrological regimes in this type of semi-arid environments. (c) 2005 Elsevier Ltd. All rights reserved.