PAKISTAN is confronting challenges of water shortage that threatens sustainability of agriculture. The current per capita water availability of about 1,066 m3 puts Pakistan in the ‘high water stress’ category.
The variation in surface water flows as a result of climate change has increased reliance on groundwater. Due to deficient surface water supplies, agricultural development has been significantly influenced by the massive use of groundwater through private tube-well developments.
The number of tube-wells has increased from less than 30,000 in 1965 to more than one million today. Groundwater abstractions through these tube-wells have gone up to 60 km3 each year, which have exceeded the annual recharge of 55 km3. The gap between replenishment and abstraction rates of groundwater is lowering the water tables significantly with more than three metres in some areas annually. Declining groundwater tables have raised many economic and environmental concerns in the country.
The water resources are under pressure because of growing population, rapid industrialisation and urbanisation, environmental degradation and climate change. Based on recent UN population growth projections, if the population continues to grow at the current growth rate, there would be 909 m3, 738 m3 and 461 m3 per capita water availability respectively for 2015, 2025 and 2050.
Agriculture is the largest water consumer. However, the competition between agriculture and industrial sector has started to increase. The current domestic water consumption of eight per cent is expected to reach at 15 per cent by the next two decades, while storage capacity of major reservoirs is on gradual decline. Due to heavy load of sedimentation, Tarbela reservoir has lost 3.67 billion cubic metres of its gross initial storage capacity and Mangla reservoir has lost 1.21billion cubic metres. Although, raising of existing dams would add to their storage capacity, it would hardly go beyond the initial storage capacity. Hence, until new storage dams are constructed there will be progressive reductions in the active storage which will not only change the overall water availability, but also have serious impacts on requirements for irrigation.
The Indus River basin depends on approximately 50 per cent of its runoff from snow melt and glacier melt originating from upstream mountains. Thus climate change will not only lead to significant variations in the temporal and spatial runoffs in the Indus basin, but will also change groundwater ‘renewability’.
The growing water demands have reduced flows for environmental purposes in the Indus basin. On average Pakistan diverts 73 per cent flow of its rivers to the canal system and in drought periods the Indus River basin does not have sufficient water to support highly water dependent ecosystems. While it is inevitable to release more flows for environmental purposes, there is no possibility to compromise on agricultural water demands.
Undoubtedly, the use of groundwater has changed the agricultural profile of the country. But, overdrafting of groundwater aquifers has led to many negative environmental externalities like land subsidence, salt water intrusion and secondary salinity, etc.
There is a need to restrict to sustainable levels. However, groundwater management should be well-integrated with mainstream water management projects and policies.
The future groundwater management strategies should not be based on conventional wisdom — where it exists… is used to meet growing water demands— but rather on supply and demand management strategies under consideration of efficiency objectives and environmental concerns. The front line challenge is to improve water use efficiency and productivity in order to sustain irrigated agriculture.