Impact of paddy on groundwater declination in Central Punjab

Among all Indian states, Punjab occupies more than 1.5% of the total geographical area of India (CGWB 2018). Punjab's agriculture is very intensive and has a high water requirement that cannot be satisfied by rainfall. Additionally, existing surface water resources cannot satisfy agricultural needs because canal irrigation systems completely utilize surface water resources (Kaur et al. 2012). Punjab contributes 25.5% of paddy and 35.5% of wheat to the Central pool (Singla et al. 2022). The major source of irrigation water for crops like paddy and wheat is groundwater. As a result, from 1966–1967 to 2017–2018, the area irrigated by tube wells grew from 24.5 to 71.5% (Singla et al. 2022). Over the past 50 years, the state's groundwater resources have suffered due to the rapid development of tube wells and the area under them. The availability of groundwater for agricultural purposes is a significant concern, particularly in the region of Indian Punjab. This is due to the fact that agriculture is considered the cornerstone of the livelihoods of farmers and the overall economy of the state.

Given that precipitation is a fundamental element of the worldwide hydrological cycle, the implications of anthropogenic climate change on precipitation patterns have substantial ramifications for agricultural practices (Guhathakurta & Rajeevan 2008). Seasonal monsoon rains, which fall between June and September and contribute about 75% of the country's yearly rainfall, are essential to India's agriculture and economy (Kumar & Jain 2011). The average annual rainfall across India did not show any trend between 1901 and 2015 (Guhathakurta & Rajeevan 2008). Nonetheless, over the most recent years, 1951–2015 as well as 1986–2015, the annual rainfall series exhibits a diminishing tendency (Kishtawal et al. 2010). Complicated relationships between the space-time distribution of monsoon rainfall and socio-economic demand are well established, and meteorological droughts in India typically begin with a precipitation deficit. Groundwater is under pressure as a result. Analyzing meteorological parameter trend changes and their causes accurately is one of the most difficult tasks (Kumar & Jain 2011).

In the region of Punjab, there exists a total of 150 blocks. However, it is worth noting that within Central Punjab, all blocks have been subjected to excessive exploitation (Singla et al. 2022). The potential impact of climate change on freshwater availability is a significant issue of concern. Changes in rainfall patterns brought about by climate change might negatively impact the replenishment of surface and groundwater resources. The purpose of this research is to (1) identify the precise causes of groundwater depletion and (2) assess and discuss the patterns of a few selected variables over a long- and short-term timeframe.

The daily gridded data for the maximum temperature (T_max) and the minimum temperature (T_min) for Punjab have been acquired from the India Meteorological Department (IMD) at a resolution of 1.0° × 1.0° for the duration of 1998–2019. District-wise daily rainfall data were collected for the study period 1998–2019 from the IMD at a resolution of 0.25° × 0.25°. In order to examine the behavior of groundwater over a 22-year span (1998–2019), pre-monsoon (June) groundwater level data were acquired from the Directorate of Water Resource & Environment and the Directorate of Agriculture of Punjab. A groundwater surface for different years was constructed using the water table data from observation wells and the kriging interpolation technique in Arc GIS 9.3. The groundwater level at each community in relation to the closest known groundwater depth was made easier with this technique. District-by-district data analysis was conducted (Kaur et al. 2012). The Papadakis method (Papadakis 1965) was used to compute potential evapotranspiration (PET).

In this study, two non-parametric methods (Mann–Kendall (MK) and Sen's slope estimator) were applied to notice meteorological variables' trends, and Pettitt's test was used for the detection of inhomogeneity.

The MK test was used to examine variations in annual rainfall, T_max, T_min, and groundwater depth during the period of 1998–2019 as shown in Table 2.

Var(K) is measured as estimated in the MK test (Equation (3)) and Z_1−α/2 is attained from the standard normal distribution table. In the present analysis, a 5% significance level is chosen, and A₁ = (M − P_α)/2 and A₂ = (M + P_α)/2 are measured. Q_min and Q_max are the A₁th maximum and the (A₂ + 1)th maximum of the M-ordered slope estimates (Gilbert 1987). Q_med is positive if Q_min and Q_max are both positive; if they are both negative, then Q_med is negative. In meteorological time series, a Sen's slope estimator is hugely prevalent for the rate change measurement of variables for a short or long time series. The MK test and Sen's slope methods were applied using XLSTAT.

To see the impact of paddy area on groundwater declination in Central Punjab, Pettitt's test was utilized in the time series 1998–2019 on the paddy area and groundwater depth for any abrupt change.

Since there was a noticeable shift in the series in 2008, it was split into three time periods: 1998–2008 (T1), 2009–2019 (T2), and 1998–2019 (T3). The MK test and Sen's slope were used for paddy area, rainfall, and PET during selected times.

The identification of trends is necessary for the management of water resources, particularly in the semiarid regions of the world (Gocic & Trajkovic 2013). Determining the precise cause of groundwater exploitation also requires an understanding of the trends that are altered by human activity. In the current study, during T1, groundwater depleted, paddy area rose, rainfall increased, and PET remained unchanged. It means that the increase in groundwater demand due to the increase in paddy areas might be greater than the amount of groundwater recharge from rainfall. However, in T2, there were no changes in PET and rainfall but an increase in paddy area and groundwater depletion. So, in T2, the only reason behind groundwater depletions is human activity. The paddy area increased significantly after 2008 due to 100% procurement of paddy at the centre's Minimum Support Price (MSP) and consistent economic returns for the farmers. In the T3 period, PET and paddy area increased and groundwater depleted with no changes in rainfall. So, in T3, the reason behind groundwater depletion is human activity and changes in the weather parameter (only PET). Overall, PET indicated a considerable growing trend (1998–2019), but smaller time periods showed no difference. It might be a sign that PET is exhibiting the effects of a significant, long-term fluctuation in both the highest and lowest temperatures. While maximum temperatures have climbed, minimum temperatures have decreased, which is likely responsible for the notable increase in PET (Basso et al. 2021). These results are consistent with those of Zhang et al. (2014) and Piao et al. (2010), indicating that PET has increased in recent years in line with the general warming of most of China.

The period T1 showed the largest increase in the paddy area, signifying the maximum annual increase in the paddy area. This indicates that the high water-consuming crop in the paddy region in period T1 had a considerable impact on the overall groundwater depth. Even though period T2's paddy area increased at the slowest rate annually, period T2 had an impact of period T1. All of these contributed to the groundwater decrease in period T2.

The study findings indicated that period T2 can be classified as a time influenced by human activities, while period T3 is characterized by both human activities and changes in meteorological factors. The concurrent factors of precipitation, rising maximum temperature, intensified farming practices, and increased number of pumping units are regarded as the primary causes for the notable upward trajectory of groundwater depletion.

In the region of Central Punjab, groundwater levels have been negatively affected by the impacts of climate change and rotational water withdrawal. Consequently, there exists a pressing necessity for comprehensive research and the formulation of policies aimed at enhancing agricultural resilience in the area. Water conservation and rainwater collection, groundwater control, as well as enhancing the efficiency of agricultural water usage and crop variety can help in the restoration of groundwater level.

The phenomenon of altering precipitation patterns and temperature has aggravated the issue of groundwater overexploitation. The present study employed a method of dividing the extended temporal duration into two shorter intervals, each spanning a decade, in order to discern the distinct factors contributing to groundwater exploitation in Central Punjab over these times. It has been revealed that Central Punjab is currently facing challenges arising from both anthropogenic activities and climatic variations. The imperative for the implementation of sustainable agriculture is evident. Central Punjab should develop appropriate strategies for crop contingency planning in response to climate change. The recognition of climate change as an integral element within a multifaceted system holds significant importance. To effectively operationalize knowledge, it is imperative to engage in a continuous and enduring endeavor of research, foster collaborative efforts across many disciplines, and establish strong partnerships between scholars and policy-makers. Developing a comprehensive research and application agenda is of utmost importance in order to effectively bridge the gap between academic research and practical decision-making tools for addressing the challenges posed by climate change and the resource waste cycle.

C.S. made contributions to the conceptualization and design of the study. C.S. was responsible for the production of materials, as well as the collection and analysis of data. The initial version of the manuscript was authored by C.S., R.A., and S.K. The text has been reviewed and edited by R.A. and S.K. The authors assert that they did not get any financial assistance, grants, or other forms of support while preparing the manuscript.

The authors would like to express their gratitude for the support provided by the All India Coordinated Research Project on ‘Irrigation Water Management’. We would also like to express our gratitude to the India Meteorological Department (IMD) for their provision of meteorological data.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.