Spatial and temporal analysis of standardized groundwater index (SGI); a case study of Bihar, India

Groundwater is an important natural freshwater reserve on which billions of habitants depend for their diverse utilisation. Global water demand has far exceeded the total available water resources which in turn have put a serious concern on food security. India, is one of the largest agricultural user of groundwater in the world where there has been a large scale revolutionary shift from surface water management to a widespread groundwater abstraction. Increased industrialisation, rapid population growth, climate change, changes in the land use and land cover, has influenced the extensive use of groundwater which simultaneously affects the groundwater level. Groundwater drought occurs when this groundwater level falls below the critical level. In the present study, analysis of groundwater drought of the state of Bihar, India, has been conducted using a drought index called Standardized Groundwater Index (SGI) and the spatial and temporal distribution of SGI has been reflected using GIS approach. The rainfall and groundwater data of 38 districts of Bihar from 2002-2019 has been used and the data was divided seasonally into pre- monsoon, monsoon, post- monsoon and winter seasons. Indian Meteorological Department (IMD) norms have been considered for division of seasons. Further, the trend analysis of groundwater level data of all districts of Bihar for all seasons were studied using Mann-Kendall test statistics and Thein Sen's slope estimator. The results of SGI spatial and temporal distribution showed that districts namely Aurangabad, Gaya, Buxar, Bhojpur, Kishanganj, Katihar, Kaimur, Rohtas, Nawada, Saran Chappra, Siwan, Samastipur, Supaul are prone to the critical groundwater drought condition. The trend analysis results showed that 45% of the districts were showing decline in the groundwater level particularly in pre-monsoon season.