The legacy of large dams in the United States


CNDS fellows Giuliano Di Baldassarre, Maurizio Mazzoleni & Maria Rusca have recently published an article in Ambio on large dams in the U.S, where they show how chicken-and-egg dynamics of water supply & demand can generate lock-in conditions characterized by unsustainable levels of water consumption.

Center of mass (CoM) of human population (red dots) and dams (grey dots) in the period between 1840 and 2010. The map also shows the location of the geographical center of the contiguous US (green triangle), as well as the location of dams (Lehner et al. 2011) and population density (Fang and Jawitz 2018) in the year 2010

The sustainability of large dams has been questioned on several grounds. One aspect that has been less explored is that the development of dams and reservoirs often enables agricultural expansion and urban growth, which in turn increase water consumption. As such, dam development influences, while being influenced by, the spatial and temporal distribution of both supply and demand of water resources. In this paper, the authors explore the interplay between large dams, patterns of population growth and agricultural expansion in the United States over the past two centuries. Based on a large-scale analysis of spatial and temporal trends, they identify three distinct phases, in which different processes dominated the interplay. Then, they focus on agricultural water use in the Southwest region (Arizona, California and Nevada) and explore chicken-and-egg dynamics where water supply partly meets and partly fuels water demand. Lastly, they show that the legacy of dams in the United States consists of a lock-in condition characterized by high levels of water consumption, especially in the Southwest, which leads to severe water crises and groundwater overexploitation when droughts occur.

Link to the published article in Ambio.