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

Abstract

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 expected dry spell of 7 days at Durg, of 5 days at Dhamdha, and of 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 were as high as 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.