EVIDENCES OF CLIMATIC UNCERTAINTIES LINKED GROUNDWATER VARIABILITY IN PERI-URBAN AGRICULTURAL AREAS OF DELHI P.S. DATTA and S.K. TYAGI Nuclear Research Laboratory, Indian Agricultural Research Institute, New Delhi, India. Urbanization, industrialization and population pressure induced changes in land use significantly affect agriculture in peri-urban areas. In many such areas, associated with this, inadequate availability of surface water supply, uncertain rainfall and environmental changes induce indiscriminate groundwater use, leading to problems such as, decline in groundwater levels and groundwater pollution in different parts. Nonetheless, climatic uncertainties linked atmospheric carbon-dioxide assimilation, inter-cellular carbon- dioxide partial pressure and transformation processes also affect the water-use-efficiency of plants. In this background, fusion of 18 O stable isotope imaging of groundwater, 18 O and 13 C isotopic record of water-plant-atmosphere interactions, superimposed on satellite based land use images, etc., and other information systems provided an insight into many long-term processes governing groundwater variability, which can be helpful in determining groundwater management strategies under changing environmental conditions and climatic uncertainties in Delhi region. INTRODUCTION Much of the water needs in the investigated area depend upon the hydrological cycle, and the natural recharging of water resources. Urbanization, industrialization and population pressure has significantly induced changes in land use in the peri-urban agricultural areas, with challenge of sustaining production in a limited land area. Natural resources also remain under increased pressure because of the use of land for clay pits, quarries, sewage disposal tanks and garbage dumps, and water pollution from local industrial and urban sources. Groundwater, which collects in the aquifers over thousands of years through recharge, contributes to substantial quantity of water supply mainly because of the insufficiency of the surface water supply share. In many parts, associated with this, due to uncertain rainfall, environmental changes and rise in water demand for various purposes, indiscriminate groundwater use and unplanned disposal of wastes, problems, such as, lowering in groundwater levels, decline in productivity of wells, and groundwater pollution with increasing trend are evident. Changes in the water availability as a result of climatic stresses are likely to cause impacts, generally most detrimental in regions already under existing stresses due to increases in the level of competition between potential users for water. Consequences of climatic uncertainties extend also to sharp reversals of weather patterns, vegetative feedbacks and seasonal modifications in rainfall around the globe. Climate change modifies total seasonal rainfall, evaporation, runoff, and soil moisture