Spatiotemporal Characterization of Meteorological Droughts and Its Linkage with Environmental Flow Conditions

A robust characterization and risk assessment of droughts is need of the hour considering its pervasiveness and consequences; however, a precise physical quantification of droughts is a difficult geophysical endeavor. This becomes a serious issue for India, having 18% of world's population and 4% of global freshwater, out of which 83% is used in agriculture. In this study, a detailed spatiotemporal assessment of the meteorological droughts characterized by standardized precipitation index (SPI), have been carried out over Narmada Basin, India for the time scales of 1, 3, 6, and 12 months, using the long-term monthly rainfall data from 28 stations for 63 years (1951-2013). The non-parametric Mann-Kendall (MK) test has been applied to investigate the trend of droughts at a 3-monthly (seasonal) scale. Further, to predict the environmental flow (EF) conditions from rainfall data only, the linkage of SPI with the average annual flow (%AAF) is examined over four sub-catchments (Mohegaon, Hridaynagar, Manot, and Sher) of the basin. The results reveal that the frequency and severity of droughts have increased over the last decades in the basin and varied between once in 3 to 5 years. The spatiotemporal analysis indicates that every drought event has its own unique characteristics, including its onset, severity, frequency, duration, area of influence and the magnitude of the losses caused by it. The severity of recent drought events shows a more widespread aerial extent in the region. The MK test results indicate an increasing trend in the seasonal droughts. An exquisite agreement between SPI and %AAF (used to describe the EF condition) is observed with R² ranging from 0.757 to 0.988, which shows that coupling SPI with %AAF can be effective for ungauged catchments. This work will be helpful for proper planning and management of droughts over the Narmada basin.