মে 08, 2018
A recent study published by Springer in 2019 – The Hindu Kush Himalaya Assessment (authored by 210 scientists from 22 countries), warns that these mountains could lose between one-third to two-thirds of its ice fields by 2100. Melting glaciers at this scale will initially result in greater river flows by 2050-60, increasing the risks of heavier floods, bigger landslides, excessive soil erosion, dam busts and silting of reservoirs etc. As the glacial melt begins to decline subsequently, that pattern is predicted to reverse, especially in the dry summer months, resulting in harsher droughts, and lower energy output from hydropower dams. But worst of all, tensions between neighboring communities and countries would likely increase over shared water resources.
Global warming due to greenhouse gas (GHG) emissions results in higher air and ocean temperatures. Warmer oceans mean more evaporation from the oceans, and warmer air means more moisture holding capacity of the air – resulting in bigger and heavier clouds, and bigger and heavier precipitation (rains and snow fall) events. Studies have also pointed out that higher energy in the atmospheric system is pushing the storms and clouds further north and south from the equator, depriving some regions which used to receive rains while increasing rains in others.
The case of Pakistan is unique due to the presence of the world’s tallest mountains in the north. On the one hand, the mountains would block the clouds from moving further north, and on the other, bigger and heavier clouds would drop heavier loads of water in the mountains, ultimately bringing more water into the rivers. Many scientific studies have predicted increased net precipitation in South Asia as a consequence of global warming.
In sum, Pakistani rivers will initially have more water in the drier summer months due to higher glacial melting until 2050-60, and thereafter much less; the wetter months, however, will see bigger and heavier clouds that would bring more water in the rivers; and, with more energy in the system, the frequency and severity of the extreme events, longer droughts and heavier flooding, would increase.
The current-day science, therefore, provides us with a basis to decide upon the dos and don’ts of a climate change strategy that has to deal with longer droughts, heavier flooding, and GHG emissions. What we need, therefore, is to (i) learn to live with larger floods; (ii) improve our capacity to survive longer droughts; and (iii) invoke engines of green economy that help reduce GHGs and enhance sequestration of atmospheric carbon dioxide.
Let us start with flood management, and specifically the lessons learnt from the floods of 2010. These brought in an estimated flood volume of 48 million acre feet (MAF) – more than four times the combined capacity of all dams in the country, which inundated 14.8 million acres to an average depth of 3.28 feet (1 metre). The inundation in most districts of (Pakistan) Punjab and Sindh lasted from three to four months. The large extent and long duration of inundation points to the fact that the natural landscape of the Indus Basin has developed in a way that does not facilitate free drainage on the one hand. On the other, the landscape lacks the natural capacity to absorb floods. The scale of these floods cannot be handled with existing or even additional dams. Moreover, the hydrological regime predicted for the future has more silt to choke reservoirs, bigger flood waves threatening dam bursts and little water in summer to generate hydropower. Under such regimes, thinking of building more dams even for hydropower, let alone control flood, is a risky affair.
Many national and international studies after that 2010 floods concluded that structural impacts such as backwater flow from barrages, restricted flood-carrying capacity of rivers due to engineered dykes and levees, high embankments of canals in the flood plains, and destruction of wetlands and riverine forests for agriculture combined to cause river avulsions and levee failures. The engineering and development of the Indus basin, in other words, exacerbated the flood damages. The structures could only avoid disasters within their design capacity, but beyond that, they made people even more vulnerable.
Climate change has added a layer of uncertainty on the estimation of engineering design parameters such as ‘maximum probable floods’, which are generally based on historical data. Putting cascades of dams along the rivers and constructing higher dykes to restrict river’s flooding would only increase the damages in case of failure.
Restoring capacity of riverine corridors
Management of riverine corridors and active flood plains is the key to managing large and frequent floods. What we need is to restore the capacities of riverine corridors to pass bigger floods, rehabilitate lost wetlands to absorb flood peaks, and regenerate forests in floodplains to break flood velocities and complement aquifer recharge. The estimated area of Pakistan’s riverine corridors and active floodplains is approximately 21,000 square kilometres as shown on the map. These areas are government-owned lands along 3,186 kilometres of the rivers with an average width of 6.6 kilometres. With proper management of wetlands and forests in this area, it could hold and recharge between 30 to 50 MAF of water during a flood.
No other engineering intervention can match this capacity, and the cost is much lower than building large dams. Additionally this would regenerate ecological services worth billions of dollars each year.
This approach will also help with the management of droughts. The riverbed and sand deposits within the areas shown on the map form freshwater aquifers of excellent quality. If we manage just the top 150 metres of these aquifers, they give us a storage potential of more than 380 MAF (in comparison the proposed Bhasha Dam is only 8 MAF, and the Mohmand dam less than 1 MAF). Compared to our current (wasteful) water demands of 104 MAF per year, this storage potential is enough to sustain us for more than 1,300 days. Our current storage through dams is only 30 days.
If we simultaneously start investing on both the water conveyance systems and on-farm practices to improve irrigation efficiency, current technologies can enable us to produce as much crops with less than 30 MAF. If we reach this potential, over 10-20 years, the aquifer storage of 380 MAF is enough to sustain us for 13 years.
In other words, managing aquifer recharge in the riverine corridor, combined with improved irrigation efficiencies, can literally make Pakistan secure in the event of the longest conceivable droughts.
Arresting GHG emissions and green economy
This reclamation of land would also have significant GHG emission mitigation effects. Recently presented research at the American Association for Advancement in Science (AAAS) has estimated that 10 years’ worth of GHG emissions can be wiped out by planting tress only in degraded and abandoned lands of the world. Regeneration of forests and wetlands not only synergises with the current drive of tree plantation in the country, but also dovetails with the global objectives of carbon sequestration and clean air.
Rehabilitated riverine corridors will also help create many engines of green economy such as eco-tourism, water-front intrinsic-value developments, navigation for trade and commerce, as well as supporting fisheries and aquaculture. These would benefit local communities and help the national economy.
Pakistan can present the Indus River Corridor Regeneration as a model for restoration of degraded river systems in other parts of the world.
Our investment priorities to combat the impacts of climate change, therefore, narrow down to the restoration of our riverine corridor and active floodplains. The figure schematically illustrates the concept of a restored riverine corridor.
The interventions are not structurally heavy either. Good planning and financial management can start the work without requiring huge budget allocations, foreign aid or loans. And the nature of these works is such that every small or large bit of area rehabilitated, starts giving its output without depending on other areas. There could be no better synergy. In one intervention we manage floods and droughts, we create a number of engines of a green economy, we exceed our GHG emission control targets, we restore ecological services and we present ourselves as responsible citizens of the world.
Hassan Abbas is an expert in Hydrology and Water Resources ([email protected])
Asghar Hussain is an expert in remote-sensing and geographical information systems ([email protected])