According, to data from NASA’s Gravity Recovery and Climate Experiment (GRACE), a pair of satellites that sense changes in Earth’s gravity field and associated mass distribution, including water masses stored above or below Earth’s surface, more than 26 cubic miles of ground water disappeared from aquifers in areas of Haryana, Punjab, Rajasthan and the capital territory of Delhi between 2002 and 2008. The scientists have found that ground water levels in northern India have been declining by as much as one foot per year over the past decade.
Data relating to 2006 shows a staggering fall of 2 metres in several Andhra Pradesh and Karnataka districts in comparison to previous years. Tamil Nadu was worse with levels dropping by 2-4 metres. More than 20% of monitoring wells in Punjab, Haryana, Chandigarh, Bihar, West Bengal, east Madhya Pradesh and east Rajasthan registered a decline of more than 2 metres, water fluctuation in January 2007 in comparison to the average between 1997 and 2006 revealed. Parts of UP and the hilly areas of the north registered improved groundwater use.
The 2007 Central Groung Water Board (CGWB) report states 18% of assessed units in Andhra Pradesh, 78% in Delhi, 49% in Haryana, 75% in Punjab, 59% in Rajasthan, 37% in Tamil Nadu, 14% in Gujarat and 12% in Uttarakhand are “over-exploited.” Its projections of groundwater availability for irrigation in 2025 — not surprisingly — show negative figures for Haryana, Punjab and Rajasthan.
Only in some areas, like the hilly terrain of West Bengal, Assam, parts of Meghalaya, Tripura and Jharkhand, there is rise in water levels by more than 2m as in the case in parts of the sub-Himalayas. The constant worry on groundwater is increased with the drought covering nearly 250 of the country’s 500-odd districts this year.
In Punjab, out of the 138 blocks, 103 have over exploited groundwater, five have reached critical levels and another four are nearing the red zone. The groundwater development in Punjab is 145% which means that water is being used at a rate of 45% more from underground sources than natural systems.
The pressure on groundwater is bound to increase as the government planning to battle drought by sinking hundreds of tube wells. The green states of the north are now witnessing a situation where extensive irrigation required is not adequately met by the surface water alone.
Ground water levels respond slowly to changes in weather and can take months or years to replenish once pumped for irrigation. Mr. Matthew Rodell of NASA’s Goddard Space Flight Center, answered to this question, “The layer of unsaturated soil acts as a buffer between the atmosphere and the aquifer. When it rains, the surface soil becomes wetter and surface water bodies increase in volume, but it takes time to percolate to the aquifer, and if it is a small amount of rain it may not replenish the aquifer at all. If you look at a time series of soil moisture, surface water, and groundwater, there is always a time lag between changes in the surface storages and the groundwater, also, high frequency variability in the surface stores are smoothed out in the groundwater response. It can take months or years for the aquifer to recover depending on how deep the aquifer is and how depleted it has become.”
The results of this research have been published in the latest issue of Nature. It is based on data from NASA’s Gravity Recovery and Climate Experiment satellites.