Abstract
The effects of climate change and variability on river flows have been widely studied. However the impacts of such changes on sediment transport have received comparatively little attention. In part this is because modelling sediment production and transport processes introduces additional uncertainty, but it also results from the fact that, alongside the climate change signal, there have been and are projected to be significant changes in land cover which strongly affect sediment-related processes. Here we assess the impact of a range of climatic variations and land covers on the River Thames catchment (UK). We first calculate a response of the system to climatic stressors (average precipitation, average temperature and increase in extreme precipitation) and land-cover stressors (change in the extent of arable land). To do this we use an ensemble of INCA hydrological and sediment behavioural models. The resulting system response, which reveals the nature of interactions between the driving factors, is then compared with climate projections originating from the UKCP09 assessment (UK Climate Projections 2009) to evaluate the likelihood of the range of projected outcomes. The results show that climate and land cover each exert an individual control on sediment transport. Their effects vary depending on the land use and on the level of projected climate change. The suspended sediment yield of the River Thames in its lowermost reach is expected to change by −4% (−16% to +13%, confidence interval, p=0.95) under the A1FI emission scenario for the 2030s, although these figures could be substantially altered by an increase in extreme precipitation, which could raise the suspended sediment yield up to an additional +10%. A 70% increase in the extension of the arable land is projected to increase sediment yield by around 12% in the lowland reaches. A 50% reduction is projected to decrease sediment yield by around 13%.
Highlights
Climate change is expected to alter soil erosion and sediment transport processes, the extent and magnitude of these variations are poorly understood (Peizhen et al, 2001; Pruski and Nearing, 2002)
In the present study we show that for the River Thames the extent of climate and land-use change effect is variable depending on the sub-catchment and the river reach, and, the climate change impact appears to be predominant at the catchment scale, the amount of arable land controls an important part of the total sediment production and sediment transport
This paper investigated the joint control exerted by climate change and land-cover change on suspended sediment discharge in the River Thames catchment (UK), through the use of a scenario-neutral method and the UKCP09 projections (Murphy et al, 2009)
Summary
Climate change is expected to alter soil erosion and sediment transport processes, the extent and magnitude of these variations are poorly understood (Peizhen et al, 2001; Pruski and Nearing, 2002). According to Nearing et al (2004), changes in precipitation and temperature and their interactions with land use and vegetation cover are the main climate change-related stressors that are likely to affect sediment transport in the future. These factors are expected to alter sediment production and soil loss, as well as in-channel mobilisation of sediment, phosphorus and contaminants (Mullan et al, 2012). Sediment transport is strongly affected by extreme precipitation and river discharge, owing to the non-linear relation between water discharge and. Its impact on soil erosion has been assessed, for example, by Boardman (2015) and Burt et al (2015), who detected an upward trend in average rainfall per rain day in southern England which could increase soil erosion
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