Extreme air pollution events in Hokkaido, Japan, traced back to early snowmelt and large-scale wildfires over East Eurasia: Case studies

Teppei J Yasunari,Kyu-Myong Kim,Masayuki Akiyama,Arlindo M Da Silva,Masamitsu Hayasaki,Naoto Murao

doi:10.1038/s41598-018-24335-w

Abstract

To identify the unusual climate conditions and their connections to air pollutions in a remote area due to wildfires, we examine three anomalous large-scale wildfires in May 2003, April 2008, and July 2014 over East Eurasia, as well as how products of those wildfires reached an urban city, Sapporo, in the northern part of Japan (Hokkaido), significantly affecting the air quality. NASA’s MERRA-2 (the Modern-Era Retrospective analysis for Research and Applications, Version 2) aerosol re-analysis data closely reproduced the PM2.5 variations in Sapporo for the case of smoke arrival in July 2014. Results show that all three cases featured unusually early snowmelt in East Eurasia, accompanied by warmer and drier surface conditions in the months leading to the fires, inducing long-lasting soil dryness and producing climate and environmental conditions conducive to active wildfires. Due to prevailing anomalous synoptic-scale atmospheric motions, smoke from those fires eventually reached a remote area, Hokkaido, and worsened the air quality in Sapporo. In future studies, continuous monitoring of the timing of Eurasian snowmelt and the air quality from the source regions to remote regions, coupled with the analysis of atmospheric and surface conditions, may be essential in more accurately predicting the effects of wildfires on air quality.

Highlights

On July 25–26, 2014, Hokkaido suffered a serious air pollution and Sapporo city cautioned its citizens on July 26 for the first time since PM2.5 observations were started in Sapporo in 2010
In July 2014, significantly large-scale wildfires occurred in the Sakha Republic (Russia) and elevated PM2.5 levels were observed on July 25, both in the areas directly affected by the fire and in faraway locations such as Hokkaido (Japan) (Fig. 1)
The observed PM2.5 in Sapporo due to the smoke transport peaked on July 25 (Fig. 2; see Website 1 and ref.31), which was closely reproduced by the calculated PM2.5 with NASA’s reanalysis data, MERRA-2

Summary

Introduction

On July 25–26, 2014, Hokkaido (the northernmost prefecture in Japan) suffered a serious air pollution and Sapporo city (the most urbanized city in Hokkaido) cautioned its citizens on July 26 for the first time (http://www. city.sapporo.jp/kankyo/taiki_osen/chosa/documents/140912_pm_youin.pdf; hereafter called, Website1) since PM2.5 observations were started in Sapporo in 2010 (the information only available in Japanese: http://www.nies. go.jp/igreen/tj_down.html). A previous notable study by Westerling et al reported that early snowmelt could generate more wildfires in the following season over the US22 They found a negative correlation between the center of mass of stream flow, an indicator of the timing of spring snowmelt, and wildfire frequency in western North America, implying that early snowmelt is relevant to wildfire activities[22]. We start by focusing on the large-scale wildfires that produced the smoke transported from Siberia to Japan in July 2014, and their significant impact on the air quality in a big urban city in Sapporo, Japan (Website 1). Our outcomes would provide a basis for future scientific discussion in studying the effect of wildfires on air quality, especially in the region spanning from East Eurasia to Japan

Methods

Results

Conclusion