Water management for supplemental irrigation based on rainfall characteristics of Ranchi district, India

Abstract

Rainfall and drought assessment is essential in identifying the water supply trends, detecting the probability of drought occurrence, and managing the irrigation water for assured crop growth. Forty two years (1971-2012) of daily point rainfall data were analyzed for Namkum, Ranchi station for assessment of basic rainfall characteristics, number of rainy days and distribution of rainfall across the seasons in a year to plan the supplemental irrigation for the rabi season crop. Trend analysis of rainfall amount and number of rainy days was done by non-parametric Mann-Kendall test and Sen's slope approaches. The drought analysis was done by using standardized precipitation index (SPI). The results showed a decreasing trend in annual rainfall for most of the months and significantly decreasing trend during February (-0.51 mm yr-1) and July (-2.66 mm yr-1) months. The annual and winter rainy day showed a statistically significant decreasing trend with the magnitude of -0.38 and -0.09 days yr-1, respectively. The annual drought analysis revealed that out of forty two years of study duration, only one extremely severe drought occurred in this region in the year 2010. Thus, traditional water harvesting structures such as Jalkunda as well as farm pond should be constructed to harvest the excess rainfall in the rainy season. The harvested rainfall can be used to provide supplemental irrigation during rabi crop season as well as in the monsoon season during prolonged dry spells. The outcomes of this study would help in water management studies for providing supplemental irrigation to the crops at their critical stages.