Water Sustainability and Climate

This research focuses on water and climate with a focus on large infrastructure. Current focus by SASWE for infrastructure is on large dams and cities. There are numerous large cities located in close proximity and downstream to a large dam. Many such large cities are often ‘Dam-reliant’ due to their existential need for a steady supply of water, flood control, power and, in some cases, food generation that are sustained mostly with the upstream dam’s water. Overall, dams are responsible for supplying water for about 40% of world’s irrigation, 20% of global food production and 10% of power generation, all of which play a key role in maintaining the integrity and functional resilience of the nearby cities. Thus, a fundamentally novel concept for the infrastructure community- called ‘Dam-reliant Large City Infrastructure’- needs to be recognized for improving future resilience of cities under changing patterns of extreme meteorological events. From a research standpoint, dams and nearby cities need to be studied together because future patterns of extremes in weather are expected to be significantly different from the past records that were used for design/operation of dams and for consequential flood risk assessment of downstream infrastructure.

Figure 1. Upper left panel: Location of large dam-reliant cities with population exceeding 1 million within 100 km of a large dam (from Hossain et al., 2012). Upper right panel: relative share of dam infrastructure between developed and developing nations; Lower left panel: Construction timeline for major dams; Lower right panel: Distribution of large dams according to their main application. The data on dams was obtained from the GRanD database containing information on 6000 dams around the world (Lehner et al., 2011).

SASWE group believes that a fundamentally missing part in current approaches to assessment of future infrastructure resilience is the bottom-up (contextual) human-driven changes to extreme weather at the local-regional scale due to landscape changes. At a minimum, the dam-reliant large city, as it grows, changes the pre-existing landscape to open bodies of water, impervious land, deforested and irrigated lands. Such predictable changes lead to changes in surface albedo, surface roughness, sensible/latent heat fluxes and eventually to altered patterns of extreme weather not considered pro-actively during the design stage. Recent work by SASWE group has demonstrated, through high resolution weather and flood modeling, that such anticipated landscape changes modify pre-dam estimates of design storms (probable maximum precipitation) and design floods (probable maximum floods) that are critical to flood risk management and downstream infrastructure resilience. On the other hand, the more commonly used approach of top-down (global) general circulation model (GCM) projections on climate, suffer from large uncertainty and are unlikely to have decision-making value at the local-scale. A specific question that SASWE group is trying to answer is: How structurally different are the assessments of future infrastructure resilience for dam-reliant cities when approached from bottom-up (using high resolution weather-flood-urban models) and top-down (using only low resolution GCM climate projections) contexts? How can these contrasting approaches be synergized for more robust assessment of future resilience in the 21st century under a changing climate?

Figure 2a. Distribution of dams in the United States that will be older than 50 years by 2020 (darker shades represent higher %). Source: Hossain et al., 2010; National Inventory of Dams, USACE.

Figure 2b. Top-down (more common) and bottom-up (the proposed) approaches to derive adaptation policies on infrastructure resilience against inundation (flooding) from future climate.

In the US, more than 85% of large dams will be over 50 years old by 2020, thus exposing many downstream cities to potentially unknown flood risks from a combined loss of storage, altered magnitude of heavy storms, floods and frequency of unscheduled flow release. Large dams also continue to be built near expanding cities at a significant rate in developing nations. Such new and proposed large infrastructure projects urgently need to learn from experiences of the ageing dam-city infrastructure in the US for improved resilience. The broader impact of the proposed project will therefore be on defining best practices for risk management of ageing and emerging dam-city infrastructure in the 21st century. Completion of the project will initiate a new breed of civil engineers who are equipped with skills and the mindset to handle the multi-faceted issues of infrastructure resilience, particularly at the intersection of weather and human impacts. In the long-run, the proposed project will improve the nation’s infrastructure that currently suffers from a D-minus grade assigned by the American Society of Civil Engineers.