It is a known fact that urbanisation has negative impacts on waterways and catchments due to pollution and deteriorating water quality. However, it is fairly unknown what the impacts of climate change to the hydrological flow regime, ecosystems, and aquatic life within the catchment system.
This study focuses on Lucas creek catchment in Auckland and examines the impacts of climate change to 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 area is urbanised. Over the last few decades the area been developed for residential and commercial use, 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 the 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 to warm climates that will also increase 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
To determine climate change impacts on the hydrological flow regime of Lucas Creek, the study used “statistically and dynamically downscaled climatic variables from the seven Global Climate Models (GCM’s) under three Representative Concentration Pathway (RCP 2.6, RCP 4.5, and RCP 8.5)”. Streamflow was also observed using stormwater management models.
Global Climate Models (GCM’s) under the RCP’s 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 that was 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, evaporation was obtained.
Results and discussion
Climate change will alter the flow of the river, due to extreme weather events such as extreme rainfall and increases in temperatures, 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 meter, and 12 cubic meters in the 2090’ 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 increase flooding events.
Altered flow regime, the highs and low flows will directly affect aquatic ecosystems and animal life and organism. The magnitude and duration of flow will affect the landscape of the rivers and streams, can pollute the water, affecting aquatic life.
While increased monthly flows can benefit living organisms particularly 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: