Apr 23 2019
Mombasa is the second largest city in Kenya. It has been projected that by 2035, water demand in this city will increase by two-fold and will reach an estimated 300,000 m3 per day.
Kenya Water Resources Management Authority workers build a water quality monitoring station on the Mwache River. (Image credit: The Mwache Dam Project)
In the current humid and warm climate of Mombasa, water originates from a significant amount of precipitation that could also vary considerably as the region begins to warm in the coming years in proportion to global climate model projections. However, one aspect that is not clear from the projections is that whether the levels of precipitation will increase or decrease along with that warming.
For designers of a recommended dam and reservoir system that will be able to capture runoff into the Mwache River, the ultimate magnitude and direction of precipitation change is a key concern. Incidentally, the Mwache River now totals around 310,000 m3 per day. It is very difficult to establish the capacity of the reservoir due to the significant uncertainty in the future runoff. Such a determination is important to meet the water demand of Mombasa across its estimated lifetime of 100 years.
As a result, city planners are faced with the dilemma of whether to invest in a smaller-scale dam that might accommodate present requirements, or a costly large-scale dam to offer a reliable water supply under the driest future climate estimated by the climate models, or begin small and build capacity as required.
In order to assist cities like Mombasa to deal with such consequential decisions, a research team at the MIT Joint Program on the Science and Policy of Global Change has devised a novel, systematic method for engineering long-term water infrastructure amid the uncertainty of climate change. The planning framework of the researchers evaluates the possibilities to get to know more about regional climate change in due course as fresh observations become available, and thereby assess the appropriateness of flexible methods that incrementally add water storage capacity if the climate turns out to be drier and warmer. The framework and its application to Mombasa have been described in the journal, Nature Communications.
A new framework for water infrastructure design
The researchers discovered that the flexible method is the most cost-effective approach since it also maintains a consistent water supply to Mombasa. They reached this conclusion by utilizing the framework to compare the probable lifetime expenses of a flexible method with those of two irreversible, static options for the proposed Mombasa dam—one designed for today’s climate, and the other for the warmest and driest climate.
We found that the flexible adaptive option, which allows for the dam’s height to be increased incrementally, substantially reduces the risk of overbuilding infrastructure that you don’t need, and maintains a similar level of water supply reliability in comparison to having a larger dam from the get-go.
Sarah Fletcher, Study Lead Author and Postdoctoral Fellow, Department of Civil and Environmental Engineering, MIT
Fletcher completed most of her work on this analysis when she was a PhD student at MIT’s Institute for Data, Systems and Society under the direction of Kenneth Strzepek, co-author and MIT Joint Program Research Scientist, and also in association with Megan Lickley, co-author and former Joint Program research associate who is currently a PhD student in the Department of Earth, Atmospheric and Planetary Sciences.
At present, the Kenyan government is in the last phases of the design of the Mwache Dam.
Due to the Joint Program’s efforts to make leading-edge climate research available for use globally, the results from this study have informed the ongoing design and master planning process. It’s a perfect illustration of the mission of Global MIT: ‘Of the World. In the World. For the World.
Kenneth Strzepek, Study Co-Author and Research Scientist, MIT Joint Program
By identifying opportunities to consistently apply flexible instead of static methods to water infrastructure design, the latest planning framework may save large amounts of dollars in terms of climate adaptation investments. These savings can then be passed on to give water infrastructure solutions to a large number of resource-restricted communities facing considerable climate risk.
Incorporating learning into large infrastructure decision-making
The latest study could be the first to deal with the limitations in present water infrastructure planning, which normally assumes that present-day climate change uncertainty estimates will continue all through the entire planning timeline, one that usually spans many decades. In a majority of cases, such an assumption leads to adaptive and flexible planning options to appear less economical compared to the static methods.
Through upfront estimates of how much the city planners can anticipate knowing more about climate change in the coming days, the latest framework can allow decision-makers to assess whether adaptive methods are likely to be cost-effective and reliable.
Climate models can provide us with a useful range of potential trajectories of the climate system. There is considerable uncertainty in terms of the magnitude and timing of these changes over the next 50 to 100 years. In this work we show how to incorporate learning into these large infrastructure decisions as we gain new knowledge about the climate trajectory over the coming decades.
Megan Lickley, Study Co-Author and PhD Student, Department of Earth, Atmospheric and Planetary Sciences, MIT
With the help of this planning tool, a city planner can establish whether it is viable to select a flexible or static design method for a proposed water infrastructure system on the basis of present projections of the highest precipitation and temperature change over the system’s lifetime, together with data that will ultimately come in from upcoming observations of precipitation and temperature change.
In the latest work, the team carried out this analysis for the proposed dam in Mombasa under thousands of upcoming regional climate simulations spanning a broad range of potential precipitation and temperature trends.
For example, if you started off on a high-temperature trajectory and 40 years from now you remain on that trajectory, you would know that none of the low-temperature design options are feasible anymore. At that point you would have exceeded a certain amount of warming, and could then rule out the low-temperature-change planning option, and take advantage of an adaptive approach to increase the capacity.
Sarah Fletcher, Study Lead Author and Postdoctoral Fellow, Department of Civil and Environmental Engineering, MIT
Upcoming developments on the planning framework may integrate analysis of the potential to know more about other sources of uncertainty, like the growth in demand for water resources, at the lifetime of a water infrastructure project.
The MIT Abdul Latif Jameel Water and Food Systems Lab and National Science Foundation supported the study.