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Scientists Project Rainfall Frequency and Intensity Over Next 30 Years

March 24, 2014

University of Hawaii; 2011 – Manoa have projected an increased frequency of heavy rainfall events but a decrease in rainfall intensity during the next 30 years (2011-2040) for the southern shoreline of Oahu, according to a recent study published in the Journal of Geophysical Research.

178122558Chase Norton, a Meteorology Research Assistant at the School of Ocean and Earth Science and Technology (SOEST) at UH — Manoa, and colleagues (Professors Pao-Shin Chu and Thomas Schroeder) used a statistical model; rainfall data from rainfall gauges on Oahu, Hawaii; and a suite of General Circulation Models (GCMs) from the Intergovernmental Panel on Climate Change (IPCC) to project future patterns of heavy rainfall events on Oahu. GCMs play a pivotal role in the understanding of climate change and associated local changes in weather.

Heavy rainfall and flash floods are common in the Hawaiian Islands due to their steep terrain, rain‐producing weather systems, and abundant moisture supply. They have caused multimillion dollars damage to homes, properties, roads, agriculture, and other sectors. Environmentally, heavy rainfall and runoff events in Hawaii, which are likely to cause slope and coastal erosion, pollutant discharges to the near shore marine environment, coral reef degradation, among others, are expected to change as Earth undergoes an unprecedented warming. Given the socioeconomic repercussions resulting from past storm events, it is of considerable interest to investigate changes in the frequency and intensity of heavy rainfall events in Hawaii, particularly for Oahu, as it is the most populous island in Hawaii.

“The results presented in this study may benefit many agencies who are concerned with floods and relevant policy-making in the face of climate change,” says Chu, UH – Manoa Meteorology Professor, Hawaii State Climate Office Director, and co-author of the study. “For instance, changes in rainstorm intensity may be a serious consideration in aquifer management – as precipitation is the primary water source for streams and groundwater supply.”

Norton, Chu, and Schroeder would like to use the IPCC GCM simulations and extend the rainfall model to project future events in other locations. They also plan to use a high resolution regional climate model to project future changes in water resources in the Hawaiian Islands.


Story Source:

The above story is based on materials provided by University of Hawaii ‑ SOEST. Note: Materials may be edited for content and length.


Journal Reference:

  1. Chase W. Norton, Pao-Shin Chu, Thomas A. Schroeder. Projecting changes in future heavy rainfall events for Oahu, Hawaii: A statistical downscaling approach. Journal of Geophysical Research, 2011; 116 (D17) DOI: 10.1029/2011JD015641

Filed Under: Climate Change, Rainfall

Documented Decrease in Frequency of Hawaii’s Northeast Trade Winds

March 24, 2014

Source: University of Hawaii ‑ SOEST, Date: October 2012:

Summary: Scientists have observed a decrease in the frequency of northeast trade winds and an increase in eastern trade winds over the past nearly four decades, according to a recent study.

Clouds and rain over Oahu Hawaii

Clouds and rain, as seen here over the island of Oahu, Hawaii, are influenced by trade wind patterns. Credit: Chris Ostrander – University of Hawaii at Manoa, SOEST

Scientists at University of Hawaii at Manoa (UHM) have observed a decrease in the frequency of northeast trade winds and an increase in eastern trade winds over the past nearly four decades, according to a recent study published in the Journal of Geophysical Research. For example, northeast trade wind days, which occurred 291 days per year 37 years ago at the Honolulu International Airport, now only occur 210 days per year.

Jessica Garza, a Meteorology Graduate Assistant at the School of Ocean and Earth Science and Technology (SOEST) at UHM; Pao-Shin Chu, Meteorology Professor and Head of the Hawaii State Climate Office; Chase Norton; and Thomas Schroeder analyzed 37 years of wind speed and direction, and sea level pressure data from land-based weather stations, buoys and reanalysis data.

Persistent northeast trade winds are important to the Hawaiian Islands because they affect wave height, cloud formation, and precipitation over specific areas of the region. When trades fail to develop the air can become dormant and unpleasant weather can develop.

Furthermore, Chu explained that the trades are the primary source of moisture for rain, and that a dramatic reduction could fundamentally change Hawai’i’s overall climate.  “We have seen more frequent drought in the Hawaiian Islands over the last 30 years,” he noted. “Precipitation associated with the moisture-laden northeasterly trades along the windward slopes of the islands contributes much of the overall rainfall in Hawaii.”

According to the National Drought Mitigation Center’s State Drought Monitor, nearly 50% of land in Hawaii has experienced some degree of drought during the past year.  While previous research has focused primarily on changes in trade wind intensities, this work, along with Chu’s 2010 study, is among the first to show changes in trade wind frequencies.

“In 2010, we only studied the trade wind changes at four major airports in Hawaii (Honolulu, Kahului, Hilo, and Lihue). In the current paper, we expanded our study to include four ocean buoys in the vicinity of Hawaii and a large portion of the North Pacific,” Chu commented.  In the future, these scientists will be using model simulated data to further understand the dynamics of rainfall and trade winds, and estimate future patterns.


Story Source:

The above story is based on materials provided by University of Hawaii ‑ SOEST. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jessica A. Garza, Pao-Shin Chu, Chase W. Norton, Thomas A. Schroeder. Changes of the prevailing trade winds over the islands of Hawaii and the North Pacific. Journal of Geophysical Research, 2012; 117 (D11) DOI: 10.1029/2011JD016888

Filed Under: Climate Change, Rainfall

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