hawaii rainfall
February 5, 2015

Heavy rainfall events becoming more frequent on Hawaii

Brett Smith for redOrbit.com - Your Universe Online

Possibly the latest evidence of climate change, a new report from researchers at the University of Hawaii has found that heavy rainfall events are becoming more common on the Big Island of Hawaii.

The new study, published in the International Journal of Climatology, examined extreme precipitation events and the regularity with which they take place on three islands in Hawaii – Oahu, Maui and Hawaii Island.

While heavy rainfall incidents have become more regular throughout the last 50 years on the Big Island, the reverse is detected for Oahu and Maui to the west, according to study data taken from 24 weather stations on the three islands. On Maui, rainfall extremes have become more uncommon in the last 50 years. This study also showed an east-to-west difference in how precipitation patterns are affected by a shifting climate.

“In the past, the frequency of heavy rainfall events was assumed to be fairly constant,” said Pao-Shin Chu, professor of atmospheric sciences at UHM. “However, because climate is changing, the assumption of stable precipitation climatology is questionable and needs to be reconsidered.”

“Changes in the frequency of heavy rain events have repercussions on ecological systems, property, transportation, flood hazards, and engineering design – including sewage systems, reservoirs and buildings,” Chu added.

This study also gave clues on why and how the regularity of precipitation extremes has evolved over the last five decades. Chu and Chen discovered a greater amount of extreme rain events during La Nina years and the contrary was true during El Nino years.

A study published in 2013 revealed that climate change caused El Nino to be highly active during the 20th century.

Using records of tropical tree rings, the study team found that El Nino was unusually active in the late 20th century compared to all other times over the past seven centuries. Previous research has shown that tree rings can act as a fairly reliable record of past climate events. The study included more than 2,200 tree-ring chronologies representing 700 years of data.

“In the year after a large tropical volcanic eruption, our record shows that the east-central tropical Pacific is unusually cool, followed by unusual warming one year later. Like greenhouse gases, volcanic aerosols perturb the Earth’s radiation balance. This supports the idea that the unusually high (El Nino) activity in the late 20th century is a footprint of global warming” said study author Jinbao Li, a scientist working at the International Pacific Research Center, University of Hawaii at Manoa.

“Many climate models do not reflect the strong (El Nino) response to global warming that we found,” added co-author Shang-Ping Xie, an oceanography professor at University of California at San Diego. “This suggests that many models underestimate the sensitivity to radiative perturbations in greenhouse gases. Our results now provide a guide to improve the accuracy of climate models and their projections of future (EL NINO) activity. If this trend of increasing (El Nino) activity continues, we expect to see more weather extremes such as floods and droughts.”

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