Assessment of dependable rainfall and water availability for sustainable watershed management: A case study of Vihokhu Watershed, Dimapur, Nagaland

Abstract

The present study evaluates dependable water availability and rainfall variability in the Vihokhu watershed, located in Kuhuboto Block of Dimapur district, Nagaland, covering a geographical area of 807 ha. The watershed receives an average annual rainfall of 1564.11 mm (2007-2021), yet much of this rainfall is lost as surface runoff due to steep slopes, jhum cultivation, deforestation and improper land management, resulting in soil erosion and reduced agricultural productivity. To support sustainable watershed management and improved crop production, weekly dependable rainfall at a 75% probability level was analyzed to determine water availability throughout all 52 weeks of the year. Results indicated that the monsoon period consistently spans from Standard Meteorological Week (SMW) 24 to SMW 42, with June-August being the wettest months (285.16 mm average rainfall), while January, February and December are the driest (18.65 mm). Although the region receives substantial annual rainfall, its uneven temporal distribution creates water-deficit weeks during the crop-growing season, necessitating supplemental irrigation. Based on the cropping pattern and water requirement analysis, an irrigation schedule was developed to bridge these deficits through water harvesting and storage structures. The study underscores the significance of dependable rainfall analysis for planning soil and water conservation interventions in hilly watersheds. The findings provide a scientific basis for improving water resource management, enhancing agricultural productivity and strengthening the socioeconomic resilience of communities within the Vihokhu watershed.