Dry and wet spell analysis for agricultural planning in Durg district of Chhattisgarh

Daily rainfall data of 20 years (1991–2010) for Durg, Dhamdha and Patan blocks of Durg district in Chhattisgarh were analyzed for the purpose of agricultural planning. Study revealed that on an average, 138, 139 and 137 days were observed as dry days (rainless days) in Durg, Dhamdha and Patan blocks, respectively during entire monsoon season. Similarly, almost equal numbers of dry days were found in all the three blocks at individual growth stages of rice crop. During complete reproductive phase, including flowering stage, 22–23 dry days occurred at the three study blocks out of 28 days of this phase that fell during 37 to 40 standard meteorological weeks (SMWs). Probability analysis of continuous dry days based on Gamma distribution revealed that during flowering stage (37–38 SMW), an expecteddry spellof 7days at Durg, of 5 days at Dhamdha, andof 4 days may be experienced at 25% probability of exceedance that was considered for rice crop planning, indicating less proneness of drought condition at Patan in comparison to Durg and Dhamdha blocks. At reproductive phase, 3 to 4 days dry spell might occur at all the study blocks. Markov Chain modeling of dry spells indicated that during nursery and reproductive stages of rice crop, the initial and conditional probabilities of dry weeks wereas highas 71–90% indicating severe shortage of rainfall and supplemental irrigation was a must for realizing good yields at all the blocks. During seedling and vegetative growth stages, probability of getting wet weeks was found higher and during that period excess rainwater needs to be harvested in on-farm water harvesting structures that could be recycled during flowering and reproductive stages. It was also suggested to plant rice crop in such a way that critical growth stages may coincide, as far as possible, to the period when probability of rainwater occurrence is higher.