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Groundwater currently provides more than 50 per cent of the total water available at farm gates and in many areas it is the sole resource for domestic use.
However, dropping groundwater levels indicates that extraction rate is far bigger than the real capacity of these resources. Therefore, groundwater availability is expected to decrease significantly in the future which will have serious consequences on food security. Groundwater use is also affiliated with high energy demand and carbon footprint.
Currently, the country houses around 1.2 million private tubewells, of which, 800,000 are in Punjab alone. The estimated number of users is over 2.5 million farmers. Investments on the installation of private tubewells are to the tune of $400 million whereas the annual benefits in the form of agricultural production are around $2.5 billion.
However, the unregulated and uncontrolled use of groundwater has diminished the relative accessibility. The continuous decline of groundwater table has resulted in the serious imbalance between discharge and recharge and many wells have become dry. Water tables continue to decline and the quality deteriorates.
Groundwater has become inaccessible in five per cent and 15 per cent of the irrigated areas of Punjab and Balochistan respectively. If the trend continues, this area is expected to increase to 15 per cent in Punjab and 20 per cent in Balochistan by 2020.
On an average, 45 million acre feet (maf) groundwater is pumped annually. About 200,000 tubewells are operated by electric motors whereas the rest are run by diesel engines of various capacities. Out of the total 45maf, about 10maf of groundwater is lifted using electric pumps, while for others diesel pumps are used.
Considering that overall pumping efficiency of the electric pumps is at 40 per cent and electricity transmission and distribution losses is at 25 per cent, pumping 10maf of groundwater requires six billion kWh of electricity. Diesel powered tubewells are even less efficient but they lift water to a smaller head.
Moreover, diesel does not face the transmission and distribution losses. A litre of diesel provides the equivalent of 10 kWh of energy. The utilisation factor of private diesel tubewells is between 10-15 per cent (1350 hours per year).
Therefore, total annual fuel consumption of one million diesel tubewells would be 3.5 billion litres. This means that, on average, extracting one cubic metre of groundwater requires 0.820 kWh of energy, which is equivalent to lighting up a 100 watt bulb for more than eight hours.
Annually 3.8mmt of carbon emits as a result of groundwater irrigation. Of this figure, which is roughly 1.2 per cent of the country’s total carbon emission, 1.4mmt of CO2 equivalence emits through electricity consumption and 2.4 MMT of CO2 equivalence through diesel combustion.
In other words, on an average, extraction of every cubic metre of groundwater comes with a hidden environmental cost of 80g of carbon emission. Therefore controlling energy demand in the agricultural sector can be a big step forward in limiting overall carbon emissions.
There are two potential ways of reducing energy use in agriculture. The first option is to increase overall pumping plant efficiency through the use of high quality pumps and electric motors. However, such interventions are expensive and, more importantly, have limited scope. The second option is to reduce the irrigation water demand through improved irrigation techniques. This option is particularly relevant to Pakistan where water use efficiencies are extremely low.
This means that a significant amount of the applied irrigation water is lost by seepage from the irrigation canals and farm fields. The impact of this is not only wastage of water, but it also leads to water-logging and soil salinity problems. Even though much of this lost water is now captured by the extensive groundwater pumping and used in downstream, this does not apply to the saline groundwater areas.
Considering the water scarcity in the Indus basin, many researchers have shown that adoption of improved irrigation practices can save up to 20maf. This water is usually contributed through groundwater extraction as evident from declining water table conditions in most of the canal command areas.
Reducing of 20maf groundwater will reduce the diesel consumption by 2.2 billion litres (62 per cent) and 1.5mmt of CO2 equivalence (40 per cent). With these reductions, total consumption of diesel will reduce to 1.3 billion litres and CO2 emissions from 3.8 to 2.3mmt of CO2 equivalence. Thus, enhancing water use efficiency in agriculture can help in coping with water, energy, and climate change issues in the agricultural sector.
The writer is a senior environmental specialist, National Development Consultants, Lahore.