Report on impact of climate change on groundwater recharge released
The first report of a national project to investigate the impact of climate change on groundwater resources has been released, describing the results of a modelling study on the impact of climate change and variability on diffuse dryland groundwater recharge (the recharge across the landscape under non-irrigated land use) in the Murray-Darling Basin.
The report is the first output of the ‘Investigating the Impact of Climate Change on Groundwater Resources’ project. The research was undertaken by CSIRO in collaboration with the Murray-Darling Basin Authority to support development of the Basin Plan.
- estimated the historical long-term average dryland diffuse groundwater recharge rate (the 'baseline') across the Murray-Darling Basin
- investigated the variability, within the time series, of recharge as an aggregated annual average over 15 and 50 year periods
- estimated the change in annual average recharge under a range of potential future climate scenarios for 2030, as derived from global climate models.
Groundwater makes up 16% of the water used in the Murray-Darling Basin, with a much higher proportion used during drier periods. Much of this water comes from relatively few, but stressed, groundwater systems. The proportion of use in these systems could be affected if the rate of groundwater recharge to the systems is changed, for example, by climate change.
Across the Murray-Darling Basin as a whole, diffuse dryland recharge is the dominant recharge mechanism. Other mechanisms, such as flooding, irrigation and losses from streams to groundwater, can also be regionally important, especially for some of the more stressed groundwater systems, but these types are also affected by water allocation and surface water management regimes. The full effect of climate change on all recharge mechanisms can only be assessed once a future surface water management regime is agreed.
The study found that overall, the effect of climate variability, as aggregated over 15 years, appears to be greater than that of the climate change scenarios. The effects of climate variability and climate change on dryland recharge are not spatially uniform across the Murray-Darling Basin:
- The median annual average 15-year recharge within the historical climate is very close to the baseline recharge.
- The median annual average 15-year recharge within the median future climate shows a small increase in recharge when averaged across the Murray-Darling Basin, although some areas show a decrease in recharge.
- The extreme wet scenario (wet future climate, wet 15 years) shows an increase in recharge of greater than 50% almost everywhere in the Murray-Darling Basin.
- The extreme dry scenario (dry future climate dry 15 years) shows a decrease in recharge of up to 50% across the Murray-Darling Basin.
For the larger regional groundwater systems, changes in groundwater storage (as another important parameter in groundwater resources assessment) over a 10-year planning horizon will be relatively small. Hence, there is greater potential to use an adaptation strategy for those storages than there is for local fractured-rock aquifers.
The report is the first output of a $1.5 million project, commenced in August 2009, which will lead to recommendations on how climate change can be included in National Water Initiative-consistent groundwater management and planning processes.
More information is at http://www.nwc.gov.au/www/html/2438-climate-change-and-groundwater-.asp?intSiteID=1