Abstract:
Floods in India affect millions of people during the summer monsoon (June-September) every year. Atmospheric factors, land surface conditions, and moisture source and pathways ride a combined signature in producing floods in rain-fed river basins. However, floods in Indian river basins are mostly studied considering the role of extreme precipitation, and critical contribution of factors related to land and atmosphere is often neglected. Using the Narmada River basin in central India as a testbed, we investigated the combined signature of extreme precipitation, soil moisture, and moisture sources on floods in the basin during 1951-2018 period. We find that most of the high-flow events in the basin occur during August and September and, about 80% of them are caused by extreme precipitation combined with higher antecedent soil moisture. The major flood producing storms in the Narmada basin are linked with high amount of vertically integrated water vapor flux, low mean sea level pressure, and strong winds. The Arabian Sea is the primary moisture source for the flood producing storms. However, previously unrecognized north Indian plain is also a dominant source of flood producing storms in the basin during the mid and late monsoon season. The moisture recycled from land-surface predominates the moisture sources of storm events in the upstream sub-basins while the contribution of moisture from the Arabian Sea is higher in the downstream sub-basins. These combined linkages of land, ocean and atmosphere, can assist in developing skillful early flood warning system for the Indian river basins.