Rainfall analysis based rice crop planning in Durg district of Chhattisgarh

Daily rainfall data for 20 years (1994–2013) were collected from Durg, Dhamdha and Patan Blocks of Durg district of Chhattisgarh and other climatic data on minimum and maximum temperatures, relative humidity and evaporation etc. for the same period (1994–2013) were collected from Durg Block only. Using rainfall and evaporation data, weekly and seasonal mean rainfall, expected rainwater availability at given probability levels and ET demands of the rice crop at different growth stages were estimated and analyzed. Analysis revealed that mean annual rainfall for the three study Blocks was found to be 1067.9, 908.7 and 1088.8 mm, respectively and 98% amount of the total annual rainfall occurred during monsoon season itself. Out of 20 years, 20, 11 and 25% years were observed as excess rainfall years; 25, 23 and 28% as normal rainfall years and rest 55, 66 and 50% as deficit rainfall years at Durg, Dhamdha and Patan Blocks, respectively. It indicates that larger rainfall deficiency is observed at Dhamdha Block as compared to other Blocks. Probability analysis of weekly and seasonal rainfall showed that weekly rainfall for 23–28 SMWs and 37–43 SMWs followed exponential distribution and it followed normal distribution for 29–36 SMWs, while the seasonal rainfall followed normal distribution only at all the three selected Blocks, based on Chi-square test of goodness of fit. The seasonal rainfall amounts at 75% probability levels were observed to be 743, 730 and 881 mm in Durg, Dhamdha and Patan Blocks, respectively. The expected ET demand of rice crop at the three Blocks was found to be 73 8 mm for medium duration rice variety. Considering the whole crop duration, it seems that seasonal rainfall meets the ET demands. However, the distribution of probable weekly rainfall was found to be quite erratic. The expected rainwater received at 75% probability is less as compared to ET demands at nursery stage of the rice crop. The expected weekly rainfall amounts at seedling and vegetative stages are reasonably in surplus as compared to ET demand. Therefore, this surplus rainwater needs to be harvested at the farm itself for recycling during rainfall deficit period of reproductive stage. Because, during reproductive stage (3 5–40 SM W), the total ET demand was found to be 195.1 mm whereas the expected rainwater availability at 75% probability during this period was only 73.2, 56.7 and 65.0 mm at Durg, Dhamdha and Patan Blocks, respectively, which indicates that a severe drought situation may occur at all the Blocks of Durg district. Thus, supplemental irrigation is essential at all the study Blocks to obtain good rice yields.