India is an agrarian country and more than 70 percent of its irrigated land is dependent on groundwater (Food and Agriculture Organization, 2010). With the rapid development and burgeoning population, water, without a doubt, is the most vital component. During the last fifty years, groundwater use has increased manifold—almost five times, which has led to the depletion of groundwater in many parts of India (Central Ground Water Board, 2014). Groundwater depletion due to excessive withdrawal coupled with climatic variability has been reported from time to time based on satellite observations and terrestrial measurements (Asoka et. al. 2017). Thus, it is imperative to monitor the water storage variability to enumerate water resources in different regions and influence of climate on this vital resource. Total water storage trend over a decade from 2002-2013 inferred from Gravity Recovery and Climate Experiment (GRACE) satellite data show a prominent decline in water storage over the northern part of India (Fig 1). An estimate by the National Geophysical Research Institute (NGRI) of groundwater depletion based on GRACE satellite data and hydrological models is in the order of 30-35 cubic km over the alluvial northern Indian region, which is a matter of serious concern. Field scale experiment carried out in a small area in Punjab Agricultural University campus near Ludhiana (central Punjab region), located in the water depleted region, has indicated steadily declining trend of groundwater level at the rate of 0.8 to 0.9 m/yr (Fig 2) due to the intensive rice and wheat cultivation (double crop rotation) mainly through groundwater resources. Irrigation return flow to shallow aquifers due to groundwater irrigation is calculated based on about 20 percent of the input due to rainfall and groundwater-dependent irrigation as compared to 8 per cent due to rainfall only in rain-fed locations. A water balance study using the data generated on rainfall recharge, irrigation return flow and discharge rate in the area revealed a water loss of about 166 mm in the area complementing the satellite-based observations (Chattopadhyay and Rangarajan, 2014, Yadav et al. 2010).
The water storage variability inferred from different data sets reveal two distinct patterns over India (Fig 1)—a continuous decrease, accelerated during drought period over the northern Indian alluvial region and inter-annual variability following rainfall pattern over the southern Indian hard rock terrains (Asoka et al, 2017). A positive trend in the water storage over southern Indian region is primarily influenced by the inter-annual variability caused due to rainfall variability.
India is bestowed with a large amount of rainfall, but a major portion of it gets drained as runoff. About 28 percent of total rainfall received over the Indian continent is quantified as utilisable water resource estimated from surface and ground water measurements. The uneven distribution of monitoring and utilisation pose a greater challenge to quantify the variability and availability of water resources in different parts of India (Shah, Singh and Mukherji, 2006). In addition, more than 70 per cent of the Indian territorial area is covered with hard rock formations of different nature and age and aquifer system in such terrains consists of secondary porosity. This complicates the measurement issues further.
A national aquifer mapping programme is initiated to image the 3D geometry of aquifers in different parts of India (Ahmed, 2015). The climate change with extreme events, particularly the erratic and short intense rainfall, increased gap between rainy days have led to a reduced rainfall recharge and increased runoff.
The intricate scenario of water storage variability warrants a dedicated mission mode programme to develop a scientifically guided solution. This programme may address the need for water management over India’s complex hydrological systems under variable climatic conditions, encompassing the following issues:
- Estimation of high variability of water storage and heterogeneities in the aquifer system and its periodic review;
- Emphasis on greater reliance on surface water reservoirs compared to groundwater reserves in the hard rock region;
- Implementation of water conservation measures for drinking water and appropriate artificial recharge experiment with knowledge of the sub-surface need;
- Shifting the transplanting date to periods of low evapotranspiration to minimise the declining rate in the alluvial areas along with shifting of crop types from paddy to irrigated dry crops;
- Science-based decision support tool at smaller spatial scale of hydrological unit for sustained availability of water for agriculture and human uses; and
- Public outreach on the water resources and its optimal utilisation in the absence of any practical legislation and guidelines.
Being an agrarian state with high dependence on groundwater, its availability for human consumption and agriculture assumes importance, particularly in the wake of developmental concerns for the people. Satellite observations show that monitoring and regulating the water storage variability, across different regions, become imperative because of its excessive withdrawal coupled with climatic variability.
Ahmed, S. 2015. 3D Imaging & National aquifer mapping program. Geography and You, 15 (91): 11-13.
Asoka, A., T. Gleeson,Y. Wada and V. Mishra. 2017. The relative contribution of monsoon precipitation and pumping to changes in groundwater storage in India. Nature Geoscience, DOI: 10.1038/ngeo2869.
Central Ground Water Board (CGWB). 2014.Dynamic Groundwater Resources of India (As on 31st March 2011).
Chattopadhyay, P. B. and R. Rangarajan. 2014.Application of ANN in sketching spatial nonlinearity of unconfined aquifer in the agricultural basin. Agricultural Water Management, 133: 81– 91.
Food and Agriculture Organization. 2010. Groundwater use for irrigation – a global inventory.
Shah T., O. P. Singh, and A. Mukherji. 2006.Some aspects of South Asia’s groundwater irrigation economy: analyses from a survey in India, Pakistan, Nepal Terai and Bangladesh. Hydrogeology Journal, 14 (3): 286-309.
Yadav S., E. Humphreys, S. S. Kukkal, G. Gurjeet and R. Rangarajan. 2010. Effect of water management on dry seeded and puddle transplanted rice: Part 2: Water balance and water productivity. Field Crops Research, 120 (1): 123-132.
The author is Director, CSIR-National Geophysical Research Institute, Hyderabad. email@example.com