A Centuary (1901-2000) of Rainfall climatology – A tool for crop planning

Crop production in changing environment especially under rainfed ecosystem is very difficult. One such important varying environmental factor is rainfall which affects plant growth most vitally and directly. India with its large population predominantly depends on rainfed agriculture, need timely and adequate rainfall for successful crop raising. The study on the temporal and special variations would help to design a viable cropping pattern for a specific location. In this context, monthly rainfall may be useful for planning a viable cropping pattern and related component technologies. An attempt was made to analyse therainfall data of Dharmapuri District,( lies between 11° 45’and 13° 01’ N latitudes and 77° 13’ and 78° 45’ E longitudes with an altitude of 400 meter MSL with mean annual rainfall of 851mm; mean maximum temperature of 32° C ; mean minimum temperature of 20.8° C; mean maximum relative humidity of 89.5 %; mean minimum relative humidity of 53.9 %)Tamil Nadu, India, with a purpose of identification of viable cropping pattern.Analysis of rainfall data for 100 years (1901 – 2000) for Dharmapuri district was done to find out the occurrence of Normal, abnormal and drought months and years. Monthly mean and probability analysis were also made to compute effective growing period. The data revealed that 56.3 percent of months fall under normal rainfall distribution while 34.1 % of months are drought months. Only 9.6%o months fall under excessive rainfall months and it could be observed that the occurrence of normal rain was with 71 % probability in the district. A growing period of 120 days may be planned for annual cropping from second week of August to first week of December. Double cropping could be possible with Millets / Oilseeds/ Pulses as first crop followed by Horse gram as second crop