Climate Change and Urban Waterways (Lucas Creek Catchment) Research

Urbanisation has negative impacts on waterways and catchments due to pollution and deteriorating water quality. However, the effects of climate change on the hydrological flow regime, ecosystems, and aquatic life within the catchment system are relatively unknown.

This study focuses on the Lucas Creek catchment in Auckland. It examines the impacts of climate change on its flow regiments and their consequences for the aquatic ecosystems within the catchment area.

The research presenter, Muhammad Saleem Akhter, is a PhD Candidate at the University of Auckland. He has published research papers on stormwater management, climate change, water-sensitive urban design, and hydrological and hydraulic modelling and simulations.

Lucas Creek catchment covers 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.

The study shows that all stormwater is released in the channels and causes problems like flooding, erosion, land instability, damage to plants and vegetation along the creek and catchments, and pollution, which impacts natural habitats, ecosystems, and the residents living around them.

The effect of hydrological cycle alteration in urban catchments

The study’s related literature 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;
• Urban catchments have a higher flood hazard, and due to climate change, the average rainfall will decrease, predicting 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 (GCMs) 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 to predict the hydrological regime flow under different 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-off data from atmospheric, rainfall, and evaporation algorithms 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 the GCM’s overall observation, the peak flow of Lucas Creek increased in the 2090s. The highest increase was 18.5 cubic meters, followed by 12 cubic meters under RCP 4.5.

Monthly changes to streamflow rise and fall 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, creating warm environments and increasing the intensity and frequency of rainfall and flooding events.

Altered flow regimes, with highs and lows, 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:

PHOTO CREDIT: By Bjankuloski06 – Own work, CC BY-SA 4.0, Link