Climate change has two parts, namely natural rhythmic variations, which are beyond human control and thus needs to adapt to them; and human induced trends. The two primary climate parameters that play vital role in agriculture and river water availability are temperature and rainfall. Temperature presents both trend and natural rhythmic variations but they are insignificant when compared to annual and seasonal variations wherein agriculture/crop is adapted to them. Rainfall presents natural

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... hmic variations. The rhythmic patterns are not the same at national, regional and local scales. However, there is a danger of using truncated data set of such rhythmic variation data series, which may show fictitious trend. Sometimes these are modified by climate systems like the presence of Western Ghats that helped creation of wet and dry zones on wind-ward and lee-ward sides respectively; and general circulation patterns like heat and cold waves associated with Western Disturbances. The water availability in Indian rivers showed a relationship with the rhythmic variations in rainfall. Moisture is the limiting factor for crop growth in tropical warm regions wherein most of the developing countries are located. Here temperature is not a limiting factor. The crops are adapted to them through available effective growing period in terms of moist period. In extra-tropical regions it relates to available warm period -cumulative degree days within that period -that basically relates to withdrawal and onset of winter season. In view of these variations, the average crops production at global scale or at national scale, the technology based trend dominates and masque the climate change trend by sowing small ups and downs. The climate change components are clearly seen only at local and regional scales wherein moist period is the limiting factor. In extra-tropical regions, crop production clearly reflects the climate factor.