Anthropogenic influence on monthly groundwater utilization in an irrigation dominated Ganga river Sub-Basin

In the last three decades, the low-income and highly-populated Kosi River's alluvial plain have improved its agricultural production by adapting a million groundwater pumping systems. As the farmers have less land holding for agriculture activities, site-specific water, and nutrient management are adopted for agriculture production. The study represents the impact of intensified agricultural activities aided by additional groundwater pumping system over the groundwater recharge/pumping rate. We analysed groundwater utilization variation due to farmers' empowerment through the green revolution and adaption of a million-groundwater pumping system via satellite-based Actual Evapotranspiration (AET). Throughout the year, groundwater accessibility has reduced the study area's agricultural dependency on monsoonal rainfall and allowed agricultural activities all season. In this study, hydrological modelling with spatial input data from different sources estimated monthly groundwater recharge/pumping and its variation during wet/dry years. The observed groundwater recharge/extraction was compared with the corresponding rainfall patterns and validated using measured seasonal groundwater depths. We present the relative change in groundwater recharge or extraction statistics using a set of standardized seasonal indices. Improved socio-economic condition and the risk of recurring floods/droughts has increased the dependency on groundwater aided irrigation in the region. Since the farmers have to pay for pumping fuel, they opt for more efficient groundwater-aided agricultural activities, especially in dry years. This additional dependency on groundwater has significantly increased the annual groundwater extraction rate and reduced the area's net recharge.

Automated summary

Over the past three decades, the agricultural production in the low-income and highly-populated Kosi River's alluvial plain has been improved by adapting millions of groundwater pumping systems and implementing site-specific water and nutrient management. The study shows that intensified agricultural activities, aided by additional groundwater pumping systems, have reduced the area's dependency on monsoonal rainfall and allowed for agricultural activities throughout the year. Furthermore, the research highlights the increased reliance on groundwater-aided irrigation in dry years, leading to a significant rise in annual groundwater extraction rate and reduction in net recharge.