Rivers & climate change: resilience, floods & tipping points
In their natural form, rivers are resilient, and as ‘messy’ rivers they are usually able to absorb and respond dynamically to a natural range of floods without changing form. However, this resilience is arguably under threat. Firstly, managed channels are often designed to resist change, which renders them potentially more vulnerable to disturbance by large floods that exceed design capacity. Secondly, predicted climate change is likely to see a phase-shift (upwards) in flood magnitude and frequency. Do New Zealand’s rivers have the capacity to adjust to forecast changes in flood magnitude and frequency: are they resilient in the face of predicted rapid global change? To answer this question this webinar follows two threads. Firstly, we need to understand the scale of modification that has taken place in our river systems in recent decades, which we can achieve using an index of change (Natural Character Index), comparing what is observed today (post-management) with what might be expected (pre-management). Secondly, we need to understand the potential phase-shift in flood magnitude and frequency: how big will floods become? A palaeoflood archive is presented from the Whanganui River, which reveals a connection between very large floods and the El Nino Southern Oscillation signal in New Zealand. The potential impact of large storms on river channels can be devastating, exceeding even the natural capacity to adjust without changing form when tipping points are crossed. The prospect for significant future change in New Zealand’s riverscapes must be taken seriously by society. This paper argues there is a pressing need to make room for the river and manage for (much) bigger floods.
Ian is Professor in Physical Geography at Massey University in Palmerston North, where he co-directs the Innovative River Solutions group and has been based since 2003. His research in fluvial geomorphology provides an integrated understanding of river systems at multiple spatial and temporal scales. He has completed numerous projects for stakeholders in river management and worked in catchments throughout New Zealand, as well as the UK and Europe. Prior to arriving in New Zealand, Ian completed his PhD at the University of Wales, Aberystwyth in 1996, which was followed by a lectureship in Physical Geography at Northumbria University. He is passionate about educating students in NZ’s rivers and linking geomorphology with river management.
