It is a known fact that urbanisation has negative impacts on waterways and catchments due to pollution and deteriorating water quality. However, it is relatively unknown what the effects of climate change are on the hydrological flow regime, ecosystems, and aquatic life within the catchment system.
This study focuses on the Lucas creek catchment in Auckland. It examines the impacts of climate change on its flow regiments and consequences to the aquatic and ecosystems within the catchment area.
Muhammad Saleem Akhter, the research presenter, is a PhD Candidate at The University of Auckland. He has done research papers on stormwater management, climate change, water-sensitive urban design, and hydrological and hydraulics modelling and simulations.
Lucas Creek catchment has an area of 626.35 hectares, and 55% of the site is urbanised. Over the last few decades, the area has been developed for residential and commercial use, and well-maintained drainage is in place.
All stormwater is released in the channels and causes problems like flooding, erosion, land instability and, damage to plants and vegetation along the creek and catchments, pollution, which impacts natural habitats, ecosystems, and the residents living around it, the study shows.
The effect of hydrological cycle alteration in urban catchments
Related literature of the study shows that alteration of the hydrological cycle in urban catchments adversely affects biodiversity and aquatic ecosystems are vulnerable to climate change.
- Climate change will alter hydrological cycles;
- Climate change will alter rainfall patterns in the future, causing frequency and intensity of storms which will result in flooding;
- The rise of temperatures due to climate change from the urban island heating will result from warming climates that will also increase the intensity and frequency of rainfalls;
- There is a higher flood hazard in urban catchments, and due to climate change, the average rainfall will decrease, predicting a decreased creek flow in the summer.
Determining water flow characteristics
The study used “statistically and dynamically downscaled climatic variables from the seven Global Climate Models (GCM’s) under three Representative Concentration Pathways (RCP 2.6, RCP 4.5, and RCP 8.5)”. Streamflow was also observed using stormwater management models.
Global Climate Models (GCMs) under the RCPs were employed to project various climate scenarios and what the hydrological regime flow would look like under different and various climate scenarios.
Rainfall and evapotranspiration data were also obtained from NIWA, which was downscaled to fit the study.
Models and tools were calibrated to simulate stormwater quantity and quality to determine rainfall, and run-offs data from algorithms of atmospheric, rainfall, and evaporation was obtained.
Results and discussion
Climate change will alter the river flow due to extreme weather events such as excessive rainfall and temperature increases under various climate scenarios.
Using climatic variables and projections from GCM’s overall observation shows an increase in the peak flow of Lucas creek in the 2090s. The highest increase is 18.5 cubic meters and 12 cubic meters in the 2090s under the RCP 4.5.
Monthly changes to the rise and fall of streamflow were observed for various climate scenarios under each RCP and GCM. Generally, the months of April, May, August, and September would predict the highest increase in streamflow in 2090.
The predicted rise in temperature will expand the urban heat island effect, which will create more warm environments and will result in increased intensity and frequency of rainfall and increased flooding events.
Altered flow regime, the highs and low flows will directly affect aquatic ecosystems, animal life, and organisms. The magnitude and duration of flow will affect the landscape of the rivers and streams and can pollute the water, affecting aquatic life.
While increased monthly flows can benefit living organisms, mainly the invertebrates, frequent flooding will change the landscape of the rivers and wash away vital organisms and vegetation, the study says.
Read the full paper here:
Akhter, M.S., Shamseldin, A.Y., & Melville, B.W. (2019). Climate Change and Urban Waterways: Alterations in the Flow Regime Under Multiple Ensembles [Research]. Retrieved from https://www.waternz.org.nz/Attachment?Action=Download&Attachment_id=3827