Phenology can be defined as the initiation or termination of programmed developmental stages responding to cues from day length, light and temperature.  The length of phenological stages may vary from season to season because of season to season differences in weather conditions, particularly temperature.  The impact of temperature is encapsulated in the heat unit concept.  Most variability in phenology is accounted for by variability in the time taken to accumulate a certain number of heat units using upper and lower temperate thresholds.  Therefore, different phenological stages during the growth cycle of citrus tree is affected by the extreme temperatures if the range is out of the optimum limits.  In the last few years certain phenological stages such as flowering, fruit colour, fruit sunburn and fruit maturity has been affected due the unexpected rise in temperatures. The data on the effect of climatic conditions on different phenological stages is presented with special reference to climatic extremes in recent years.  All these changes can ultimately affect the values chains.