You'll Manage

The last post talked about restricting building on floodplains as a way to manage climate change induced changes in discharge, the idea being that a natural and free flowing river is better suited to withstanding increases in discharge. A natural channel can move dynamically and adjust flows to buffer against negative impacts of increased discharge (Palmer, et al. 2008). However, the big problem is that most rivers no longer exhibit flow regimes in line with historic flow regimes, such as been the influence of humans with the construction of infrastructure such as dams and levees. For example, Poff, et al. (2007) conclude that dams have changed flow regimes in rivers across the USA – important for both humans and ecosystems.  Clearly, even without human interventions, rivers have a point at which they can no longer deal with large increases in discharge, but our own human interventions are making it worse.

We can’t have it both ways – we can’t cause increases in discharge from climate change, and then prevent natural processes that might mitigate this change from occurring. When I talk about human intervention, I mean many different things: urbanisation on a floodplain, building dams/reservoirs, and excessive water withdrawals/additions. All of these things alter floodplains such that rivers are less able to buffer and adapt to changes in discharge. These changes leave humans at risk through increased flood risk and contamination of water supplies used for consumption. Changes in yearly flow regimes can also have impacts on agricultural production, particularly in irrigation fed agriculture.

Ecosystems are also at risk too. Though they are clearly biased towards certain conclusions, the WWF (2004) and their beautifully named ‘Dam Right’ initiative identified 21 river basins at risk of severe ecological degradation, the cause being multiple (six and over) large dams either constructed, planned, or under construction within these basins. Palmer,et al. (2008) have shown that it is likely basins impacted by dam or extensive development will suffer greater changes in discharge and water stress in the face of climate change, as opposed to naturally free flowing rivers – see Figure 1.

Figure 1 - Relative percentage (%) change in discharge in large river systems around the world, from present to 2050, under two different climate models. From Palmer, et al. (2008).

We change the climate, and we also change the land. Maybe we aren’t so far from a hydrological ‘Anthropocene’.