Detecting the long-term impacts from climate variability and increasing water consumption on runoff in the Krishna river basin (India)

Variations in climate, land-use and water consumption can have profound effects on river runoff. There is an increasing demand to study these factors at the regional to river basin-scale since these effects will particularly affect water resources management at this level. This paper presents a method that can help to differentiate between the effects of man-made hydrological developments and climate variability (including both natural variability and anthropogenic climate change) at the basin scale. We show and explain the relation between climate, water consumption and changes in runoff for the Krishna river basin in central India. River runoff variability due to observed climate variability and increased water consumption for irrigation and hydropower is simulated for the last 100 years (1901-2000) using the STREAM water balance model. Annual runoff under climate variability is shown to vary only by about 14-34 millimetres (6-15%). It appears that reservoir construction after 1960 and increasing water consumption has caused a persistent decrease in annual river runoff of up to approximately 123 mm (61%). Variation in runoff under climate variability only would have decreased over the period under study, but we estimate that increasing water consumption has caused runoff variability that is three times higher.