|Mansour, M M, Hughes, A G. 2014. Land Use, Climate Change and Water Availability: Preliminary modelling of impacts of climate change and land use change on groundwater recharge for England and Wales. British Geological Survey Internal Report, OR/14/018.|
To investigate how land use and climate change can affect potential recharge, rainfall and temperature data from 11 Regional Climate Models (RCMs) from the Future Flow and Groundwater Level (FFGWL) project have been fed into the recharge model ZOODRM. This has produced potential recharge for the whole of England and Wales for three time slices (2020s, 2050s and 2080s). Allied to this, the historic rainfall and potential evaporation time series have been run for both historic and 'extreme assumed' land use change. The recharge model was run using different land cover mapping (LCM) datasets (LCM2000 and LCM2007) as well as three scenarios: all arable, all grass and all forested. A more subtle change in land use was investigated by swapping 50% of one land use for another, e.g. arable to forested.
This work has been undertaken as part of the Abstraction Reform (AR) process, a Defra led process which aims to produce a revised abstraction licencing regime. To provide consistency with the AR process the catchments used in the AR pilot study have been used (Dee, Ely-Ouse, Hampshire Avon, Stour, Tees, Trent and Derwent). In addition, the Thames Basin has been added and the results summarised for England and Wales. The results for the Thames Basin produced anomalous values which were thought to be related to the size, shape and orientation of the catchment. To investigate the impact of orientation, then two east-west and two north-south strips were also examined. The results have been presented as both difference maps of long-term average recharge and box and whisker plots for both the absolute values of recharge and the differences between the modified run and its basecase (historical simulation).
The catchments chosen have a range of sizes and are located in different climate conditions around the country. The response to climate change reflects this with recharge decreasing or increasing depending on the RCM used for the input data and time slice. The following generalisations by catchment can be made:
- Dee — lower recharge in general with increasing recharge through the time slices
- Ely-Ouse — very slight increase in recharge which increases through the time slices
- Hampshire Avon — variation depending on the RCM; no significant change across the time slices
- Stour — reduction in recharge
- Tees — reduction in recharge which decreases through time slices
- Thames — variation depending on the RCM; significant outliers with increased recharge in the 2080s
- Trent — variation depending on the RCM; increased recharge through the time slices
- Usk — increased recharge; consistent over time slices
In terms of the effect of land use change then variation due to subtle ‘real changes’ in historic land use (between LCM 2000 and LCM 2007) is small, although locally significant. Extremes of land use change are predicted to result in significant change but these scenarios are very unlikely to be realised. For the Dee, Hampshire Avon, Tees and the Usk the change in recharge due to land use change and due to climate change is comparable, for the Ely-Ouse and Trent the change in recharge less due to land use change than for climate change and for the Stour and England and Wales as a whole the change is greater. This was investigated further by swapping out different land use types, i.e. arable to forested. This showed much less variation, and was less significant in comparison with climate change.
The original question that the modelling work was to address relates to the relative changes in recharge with respect to climate change as opposed to land use change. Taking England and Wales as a whole then the order of change in recharge due to land use variation is: socio-economic land use (LCM2000 w.r.t. LCM2007) is less than spatial replacement is less than wholesale replacement (i.e. all one land use type for England and Wales). Comparing the magnitude of these changes with those resulting from climate change show that variation of recharge related to climate change falls within the range of that resulting from land use change. However, the variation of recharge due to the use of different RCMs is comparable with the overall variation of land use change.
Further work is recommended as follows:
- Understand the climate models used to feed into the FFGWL RCMs alongside an improved representation of droughts resulting from 'blocking highs' — slow moving pressure systems in the Atlantic.
- Use of National Ecosystem Assessment land use scenarios in the model to compare with the quantification of climate change runs.
- Combine the potential recharge produced with other recharge models (e.g. those produced for the Environment Agency by consultants or in the published literature) and/or produce water balances to help validate the recharge quantified.
- Undertake further analysis of the results, such as monthly summaries of potential recharge and analyse how this changes for each time slice and across catchments.
- Quantify the uncertainty in the results.