PCA driven watershed prioritization based on runoff modeling and drought severity assessment in parts of Koel river basin, Jharkhand (India)

Global warming influencing regional climate is playing a significant role in triggering recurrent drought. The current study demonstrates a PCA (Principal Component Analysis) driven watershed prioritization in a part of Koel river basin by runoff computation during monsoon season along with assessment of Vegetation Health Index (VHI) derived from MODIS satellite data during the period from 2000 to 2017. Koel river catchment area of 7,261 sq km was divided into 82 sub-watersheds based on drainage networks derived from a Survey of India (SOI) topographical map at scale 1: 50,000. High resolution satellite image of Sentinel-2 was used to prepare a land use land cover map. Soil conservation service curve number method (SCS CN) was used to estimate runoff. The result obtained from runoff estimation of 82 sub watersheds shows high runoff (50 to 60% of rainfall) with 290,000 m3 total runoff volume in the upper and middle parts of the catchment dominated by agricultural/fallow and barren lands, whereas low runoff was estimated (20 to 30%) with 29,467 m3 in the lower catchments where a large area is covered with forests. The value of satellite based VHI ranges between 23 to 53 with major parts of the area exhibiting values less than 30, reflecting poor vegetation health. Most of the sub-watersheds in parts of Ranchi, Lohardaga, Gumla and Khunti districts experienced high total runoff, with poor vegetation health index reflecting more proneness to drought. Watershed prioritization was done based on correlation among four parameters viz., rainfall, drought zones, direct runoff and total runoff through PCA. Strong correlation between total runoff volume and drought areas was used for watershed prioritization, which indicated 42 sub-watersheds (4,703 sq km) in the upper catchment required high prioritization. The outcomes of the study would help proper planning of water resources and soil moisture management to overcome the recurrent drought conditions at watershed level. HIGHLIGHTS Runoff estimation of 82 sub-watersheds has been done.; High runoff volume has been demarcated in the upper and the central part of the study area.; Areas with poor vegetation conditions have been highlighted by using drought indices.; Watershed prioritization using Principal Component Analysis by considering factors - rainfall, drought, direct runoff and total runoff - indicated that a major part of the study area is exhibiting high runoff and is severely affected by drought and therefore urgently needs watershed management based on prioritization.;