Ground water availability and, in consequence, access to irrigation in the dry season have much to do with the production of high yielding rice in the winter season that has bid a bye to low yielding traditional varieties. Irrigation, particularly ground water irrigation, is considered the lead input contributing to self-sufficiency in rice. But all that achieved so far through ground water irrigation was not a 'free launch' or costless dime.
In fact, extraction of ground water is alleged to impinge huge costs in terms of water table and withdrawal of excess water thus threatening sustainable water use. Ipso facto, concerns over the unsustainable use of underground water is mounting, although not much empirics are available. However, a recent research work by Nepal C Dey, Sujit K. Bala, AKM Saiful Islam, Ratnajit Saha and Abdur Rashid seems to shed some important light on the issue.
The findings reveal a declining trend of groundwater table over the last 30 years (1981-2011) implying that groundwater use is not sustainable in the study area such as Rajshahi, Pabna, Bogra, Dinajpur and Rangpur. The magnitude of the decline was found between from-2.3 in 1981 to -11.5m in 2011. This can be attributed mainly to the over exploitation of groundwater without having sufficient recharging aquifers. It needs to be mentioned here that shallow and deep tube wells are the major groundwater lifting devices in the study areas where the intensity of tube well use has increased, and the area per unit of tube well has drastically declined from 14.5 to 2.8 hectare during 1984-85 to 2010-11. The number of tube wells increased about nine times while the area of irrigated land increased by only about two times.
Analysis carried out by the researchers also reveals a declining trend of annual fluctuation of surrounding river water level and the discharge of the northwest region of Bangladesh over time. On an average, river water level and the discharge decreased from 20 to 19m and 90.8 to 56.9m3/sec, respectively, during 1981 to 2010. The findings also show that the declining trend of average annual river water level is positively related (R2=0.6) to the decreasing trend of groundwater table.
More disconcertingly perhaps, a decreasing trend in the wetland area has been found in the study area with around one-third of total wetlands lost during 1989-2010. Of course, the rate of decrease was much lower during 2000-2010 than that of 1989-2000. The decrease of wetland indicates a decrease of groundwater recharge resources; the findings also show a recurring of below average rainfalls over the year.
Defects in the present irrigation water management system were identified by the research. The study revealed that about four-fifths of the lifted water went to boro rice production and the rest one-fifth went to other crops. The authors estimated that about one-fifth of the water used in boro crop was excess water -- difference between the lifted water minus the irrigation water requirement of the crops. Perhaps needless to mention that the excess water increased the cost of irrigation as well as crop production in a regime where 68 per cent of the groundwater is lifted by shallow tube wells and the rest by deep tube wells.
Due to the non-availability of surface water, farmers were bound to lift groundwater which increased irrigation cost. Added to this are the price hike of agricultural inputs like fuel, electricity, agrochemicals, rent of land, labour etc. These affected the ultimate production cost threatening the overall sustainability of agricultural production of the northwest region of Bangladesh.
The cost of excess water lifted by DTW was estimated to be Tk. 2,201-7,075.8 per hectare and that of by STW was Tk 7,547.5-10,058.4 per hectare. This perhaps means that the excess water raise cost of paddy by about Tk 2 per kg. The cost of irrigation by privately owned tube wells was much higher than that of government tube wells and it was also higher in the case of diesel than electricity driven pumps. Irrigation cost per hectare of private tube wells ranged from Tk 15,000 to Tk 33,000, and that of public tube wells ranged from Tk 7,500 to Tk 11,250.
The study also casts impression on cost-benefit ratios of crops. The findings, by and large, reveal positive net return for all the studied crops. The highest benefit to cost ratio was found for lentil followed by wheat and mustard. The domestic-to-border price ratio of the crops was significantly negative except for mustard during study period. The estimates of Domestic Resource Cost (DRC) showed that Bangladesh has a comparative advantage of production in all the studied crops. The study findings implied that the production of potato and lentil would be highly efficient for import substitution. So, Bangladesh will need to enhance its supply-side capacity and pursue a broad-based diversified agricultural production and export strategy.
The survey and the Focus Group Discussions (FGDs) with farmers reveal that three-fourths of them were well aware of lowering of groundwater level in their agricultural fields, while 53 per cent complained about inadequate water during the irrigation period. Further, about 90 per cent farmers were well aware of excessive pumping as well as of drying up of local water bodies and rivers. Groundwater was invisible and remained beneath the surface. Awareness of farmers, local people along with educated ones is still in infancy. The water cycle, its interdependence of surface and groundwater, ecological balance and its services, quantity and quality, supply and demand, and above all the sustainability of the system as a whole, was poorly understood.
To achieve food security, the ecological approach with strong community participation is missing in the use of groundwater for irrigation. The use of groundwater should be ecology-friendly based on sound policy on the recharge of groundwater through conservation and community participation. A focal-point organisation at national level should be identified for the planning and execution of concerned activities. It is also imperative to follow the best irrigation management practices and climate change adaptation techniques for sustainable use of groundwater. Irrigation water was life for the north-western region in the past but now poised to emerge as woes in there.
Abdul Bayes is a Professor of Economics at Jahangirnagar University.
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