The current study excellently integrates the nature of changing groundwater levels with critical concerning drivers in both time and space. The findings clearly indicate that most of the monitoring stations in the study area are suffering a considerable decline in groundwater level, with a large amount of Sen's Slope. If the current trend continues, the average groundwater level will drop by around 2.5 meters by 2030. The study also found that groundwater usage drivers had a considerable positive impact on groundwater levels. Therefore, it is reasonable to state that, in addition to the rough hard rock structure and geology (most famous among scholars), the drivers from the human world must be included in groundwater management studies in the present study area.
Based on our research objectives, the present study can be divided into three parts. In the first part, the station-wise and geological class-wise behavior of the groundwater level of the Purulia district were examined. It was discovered that the south-eastern corner (specifically Bundwan, Manbazar, and Barabazar Blocks) and the far western end of the study district (Jhalda I, II, Joypur) suffered the most positive water level fluctuations from the local average (Gupta & Patel, 2021). This is mainly attributed to the limited infiltration capability of mica-schist and biotic gneiss geology(GEC, 2015; Haldar & Saha, 2015) and the fast-increasing manmade land-use change driven groundwater demand (Census of India, 2011). The boxplot analysis also supports the statement that the groundwater fluctuation is higher in the biotic gneiss and mica schist structure. However, the measuring stations in Blocks such as Purulia II, Para, Santuri, Balarampur, and some others, on the other hand, show lesser variations due to lower drafts (Fig. 7b) and less groundwater consumption (Gupta & Patel, 2021).
Aside from the fluctuations, the station-by-station trend analysis revealed several intriguing facts. Like despite the fact that water level fluctuations are more significant, the stations from Blocks such as Jhalda-II, Joypur, Bundwan, Neturia, and Jhalda-I indicate a growing trend in groundwater level (decreasing depth). While, the stations from the Blocks, namely Arsha, Bagmundi, Purulia I, II, Hura, and Puncha, show a rapid diminishing trend (increasing depth). This is due to the differential stages of groundwater development (Fig. 7d). If the stages of groundwater development are high, that means the draft is high, but there is a good balance between stakeholder interests and ecological needs (Villholth, 2016). Another interesting observation from the trend analysis that must be mentioned here is that several stations (Bundwan, Neturia, Santuri, Joypur, etc.) exhibit a growing trend in the pre-monsoon season but a dropping trend in the post-monsoon season (Minea et al., 2020). The findings from the relational analysis with the concerning driver explain the reason behind such characteristics. The Joypur and Bundwan Blocks are in the higher stage of groundwater management, and the Blocks like Neturia and Santuri have the lower groundwater-based irrigation area and groundwater draft. Further, Gupta & Patel (2021), in their study, found that the usage of groundwater is less in the northern and southwestern parts of the study area. However, in the post-monsoon season, most stations have shown a decline in GWL because of increasing climatic irritancies and frequent drought over the study area (Ghosh, 2009; Haldar & Saha, 2015).
Scholars in the Purulia district consistently highlighted the physical aspect of the relevant drivers whenever they discussed the groundwater system (Acharya & Nag, 2013; Chakraborty & Paul, 2004; Das et al., 2019; Gupta & Patel, 2021; Kundu & Nag, 2018). However, the results of the second part of our research have demonstrated the significance of the reverse side of the coin. It observed a similar finding to what other studies in the Gangetic basin been discovered (Das et al., 2021; Sahu et al., 2015; Dijk et al., 2020). The area under groundwater irrigation, total groundwater drafts, stages of groundwater development, and agricultural production patterns (the drivers of human water use and management) all have significant impacts on the geographical variation of groundwater levels. Halder et al., (2020), in the Silabati river basin (which is overlapped with the present study area), found that 60 percent of wells are located near agricultural land and where groundwater drafting from submersible wells is extensive, showing a significant declining trend, particularly in post-monsoon seasons.
The third section of the current study focuses on ANN-based future groundwater level prediction (Das et al., 2021; Malakar et al., 2020). The expected spatial pattern of the groundwater level for the year 2030 depicts several fascinating pieces of information. In the western bordered region of the district, while having a rising pre-monsoon trend (but a declining trend in post-monsoon) and higher stage groundwater development, groundwater depth will be more prominent by 2030. It might be due to the ongoing large-scale urbanization and massive groundwater draft in this region (Ghosh & Chakma, 2014). Apart from that, for the Kashipur Block, which has a moderate groundwater depth level, depth will rapidly increase by 2030. The higher agricultural yield (higher groundwater consumption) (Fig. 7e), the growing numbers of census towns (Census of India, 2011), and significant groundwater draft (Fig. 7b) might be the controlling components behind such decline.
Overall, the southern section of the research area, except the Balarampur C.D. Block, is highly susceptible in terms of groundwater supply in the near future, followed by the eastern Blocks of Manbazar I, II, Hura, and Kashipur. At the same time, despite the fact that the entire region is threatened by acute groundwater scarcity, the central and western C.D. Blocks (excluding Jhalda I and II) are appreciably less susceptible. Therefore, based on the study findings and facts, water harvesting structures must be developed as soon as possible in Jhalda-II, Bundwan, Manbazar, and Jhalda-I C.D. Blocks. The same may be done in the Kashipur, Hura, and Raghunathpur-I C.D. Blocks after that. Finally, places like Purulia-II, Arsha, and Joypur might be considered. Lineament junction zones, in combination with other morphological characteristics, can be used to decide where these dug wells can be built. Falling water levels are also significantly visible in much of the region, notably in Blocks like Bundwan, Jhalda-II, Baghmundi, Manbazar-II, Raghunathpur-II, and Kashipur during the post-monsoon season. Therefore, groundwater drafting regulations are very much essential from the administrative side. Lastly, one of the shortcomings of the present study is the absence of a continuous annual dataset for the parameters that are used in the relational analysis. Hence, further study is required that integrates all physical, hydrologic, and groundwater usage factors to capture the more extensive features of groundwater behaviors and offer more precise, long-term suggestions.