River flows in New Zealand have changed dramatically, according to research.

A new study has found that as the climate has changed over the past 50 to 90 years, river flows in New Zealand have changed a lot.

The study, which was carried out by researchers at Te Herenga Waka—Victoria University of Wellington and NIWA, revealed significant shifts in the average summer and winter river flows. The study’s findings are presented in a Journal of Hydrometeorology article titled “Spatiotemporal Trends in Near-Natural New Zealand River Flow.”

Even though some parts of the North Island have had a lot of rain this summer, long-term trends show that summer river flows are usually going down in these places, and it’s likely that they will get drier.

Lead author Laura Queen, a Ph.D. candidate at Victoria University of Wellington and based at NIWA, states, “Typical summer river flows have significantly decreased for much of the North Island, with the exception of Manawatu and Wellington.”

“Typical summer river flows have drastically fallen for much of the North Island, with the exception of Manawatu and Wellington,”

 lead author Laura Queen, a Ph.D. candidate at Victoria University of Wellington.

According to her, “average river flows have also decreased in the upper North Island in the winter, but significantly increased on the west coast of the South Island and in Fiordland and Southland.”

“Whether it’s natural climate cycles like El Nio and La Nia or human-caused climate change, the trends we found are the result of variations in the climate.” The next thing we need to do is figure out how much each one is contributing to these trends.

Sovereign says human-instigated environmental change is making temperatures and climatic dampness rise and wind course examples to move across New Zealand, with possibly significant thump on impacts for streams.

“Scientists anticipate that we will continue to see increases in extreme rainfall and flash flooding of shorter durations—just like we have this summer—even in locations where average river flows are decreasing, such as the upper North Island in the summer.

“The West Coast has seen an increase in rainfall as a result of changes in the strength of the southern storm track in the South Island, which has had an effect on river flow in the area.”

“We have also observed rising winter river flows in the South Island’s snow-fed catchments.” This could be brought about by shifting patterns of wind circulation that are bringing in more rain, as well as by rising temperatures that transform snowfall into rain.

The review Sovereign drove depended on long-haul information (something like a long time) from 53 destinations around the country, from the Awanui catchment in Northland to the Pomahaka in south Otago.

The study looked at rivers in wilderness areas where land use changes like deforestation or irrigation did not affect water flows. According to Queen, the researchers were able to isolate the effects of climate on river flow by concentrating on these remote rivers.

“Rather than looking at each river individually, we grouped rivers and examined how their changes had changed over time.” you look at data for a group of rivers over at least 50 years, trends that are hard to see in a single river become clear.”

She asserts that the study’s regional trends will have an impact on the management of water resources.

“The management of hydroelectric dams may be affected by an increase in winter river flow in the west South Island.” Meanwhile, the availability of water in New Zealand’s most populous region may be affected by decreasing winter and summer flows in the upper North Island.

More information: Laura E. Queen et al, Spatiotemporal Trends in Near-Natural New Zealand River Flow, Journal of Hydrometeorology (2022). DOI: 10.1175/JHM-D-22-0037.1

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