Baseline Climatology of Viti Levu (Fiji) and Current Climatic Trends1
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Baseline Climatology of Viti Levu (Fiji) and Current Climatic Trends1 Melchior Mataki, Kanayathu C. Koshy, and Murari Lal 2 Abstract: In this paper we characterize the climate at Nadi and Suva in Fiji from 1961 to the present, providing a picture of ongoing climate trends. The focus is on surface observations of air temperature and rainfall, although some information on South Pacific Ocean climate is also discussed, given its relevance for Fiji. Our findings suggest that surface air temperatures have registered increasing trends at both Suva and Nadi (the two observatory sites in Fiji iden- tified as Weather Observing Stations under the global network of the World Meteorological Organization) during the period 1961–2003. There has been a steady increase in the number of days per year with warmer nighttime temper- atures in recent decades. The rise in annual mean surface air temperature over Suva was @1.2 C over the 43-yr period considered here (at a significantly in- creasing rate of 0.25 C per decade, which is 1.5 times higher than the trends in global average temperature increase during the past century). The rate of in- crease in annual mean surface air temperature at Nadi was 0.07 C per decade. No trend in annual mean rainfall has been observed, however, at either of the locations. Significant interannual variability in annual as well as summer rainfall observed at both sites (including extreme rainfall events during the 43-yr period) can largely be attributed to El Nin˜ o–Southern Oscillation (ENSO) events and intraseasonal oscillations in the mean position of the South Pacific Convergence Zone. Baseline climatological data charac- and precipitation) with earlier periods and terize climate during a recent period, serving hence detection of possible longer-term as a reference against which to compare both changes in climate. historical and likely future climate variations. By international meteorological convention, Climatological Normals the baseline climate is usually of 30 yr dura- tion. This is long enough to encompass In the last two scientific assessment reports characteristic interannual and interdecadal of the Intergovernmental Panel on Climate variations in climate and to capture a range Change (IPCC) (IPCC 2001a,b), the period of short-term extreme climate events but still 1961–1990 was adopted as the climatological short enough to allow comparison (for the baseline, an official World Meteorological major climatic variables such as temperature Organization ‘‘normal’’ period. Convention- ally, these periods repeat at 30-yr intervals, 1 This study was undertaken as part of the activity the next being 1991–2020. Notwithstanding under the research project ‘‘Integrated Methods and this convention, with most climatological Models for Assessing Coastal Vulnerability and Adapta- data now available in digital form, it is a fairly tion to Climate Change in Pacific Island Countries’’ straightforward exercise to update 30-yr aver- funded by International START Secretariat, Washing- ages on a decadal basis, and some countries ton, D.C. Manuscript accepted 29 April 2005. 2 Pacific Centre for Environment and Sustainable have published climatological summaries for Development, The University of the South Pacific, P.O. the period 1971–2000. Box 1168, Laucala Bay Campus, Fiji Islands (fax: þ679- In selecting the baseline period, one issue 3232891; e-mail: [email protected]). to bear in mind is the closure of many manned weather stations worldwide during Pacific Science (2006), vol. 60, no. 1:49–68 the 1980s and 1990s and their partial replace- : 2006 by University of Hawai‘i Press ment with automatic weather stations. This All rights reserved has posed some problems for maintaining 49 50 PACIFIC SCIENCE . January 2006 high-quality, homogeneous records of cli- Zone, and rainfall distribution is largely con- mate in many regions. It has also reduced trolled by the large-scale cloud bands as- the total number of sites in the observational sociated with the convergence zone, the network, meaning that the station coverage migrating low pressure systems, the move- and density for the 1971–2000 data are often ment of the tropical upper tropospheric poorer than in the earlier (1961–1990) pe- troughs, and surface midlatitude systems riod. This paper therefore is confined to the such as cold fronts moving across from the baseline period of 1961–1990 as standard south. From November to April, the Fiji World Meteorological Organization clima- Islands are frequented by tropical cyclones tology in the analysis of ‘‘climatological nor- originating in the Pacific Ocean, which re- mals’’ of surface air temperature and rainfall sults in prolonged heavy rainfall and flooding at Nadi and Suva stations. of low-lying coastal areas. However, the weather in Fiji varies considerably between island regions. This is due to the dominant Geographic Location and Key Weather southeast trade winds, which helps clouds Characteristics form over the mountains on the southeastern Fiji consists of 18,376 km2 of land and in- side of the larger islands. cludes about 330 islands, of which about 100 Nadi is situated on the western side of Viti are inhabited. The largest island and popula- Levu (Fiji’s western division). The western tion center is Viti Levu, which has an area of division (Sigatoka to Rakiraki) is a relatively 10,388 km2 (Figure 1). Viti Levu is character- dry zone and is subject to large seasonal ized by high mountains, dry on the leeward and interannual climatic variation. The an- west side (Nadi) and wet on the windward nual rainfall in the dry zones averages around east side (Suva). Vanua Levu, located north- 200 cm. Typically, winter weather in the east of Viti Levu, is the second largest island Nadi region has clear or partly cloudy skies, and is slightly more than half the size of Viti much sunshine, a well-developed west to Levu. Taveuni lies to the east of Vanua Levu. northwesterly sea breeze by day (south- Equal in size to Taveuni is Kadavu, which lies easterlies are predominant at night and in all to the south of Viti Levu. Fiji’s remaining months except from August to March when islands are small and are divided into three wind is generally from the northwesterly main groups: Lomaiviti, Lau, and the Yasa- quarter), and relatively cool nights. In sum- was. mer, thunderstorm activity is common and Fiji lies in the South Pacific trade-wind responsible for brief spells of high-intensity belt of predominantly southeasterly winds. rainfall. Suva, the capital of Fiji, is situated The southeasterlies are relatively strong and on the wet eastern side of the island of Viti persistent in winter (between May and Octo- Levu (in Fiji’s central division where the an- ber). In summer (between November and nual rainfall ranges from 300 cm around the April) the winds are generally light and vari- coast to 600 cm on the higher mountains). able with a predominant sea breeze during The Fiji group of islands is surrounded by a the day. Winds from the northerly quarter huge body of water and is affected by global- are also quite common during this period and regional-scale climatic events such as El because the South Pacific Convergence Zone Nin˜ o and La Nin˜ a resulting from interannual lies just to the north of Fiji where the south- variations of the strength of the ‘‘Walker Cir- east trades and the divergent easterlies con- culation’’ over the equatorial Pacific Ocean verge. Fiji’s climate is tropical. Overall, and associated droughts and/or floods, tropi- temperatures in summer are slightly higher cal cyclones, and high waves. The islands than in the winter months as is the humidity have experienced extreme weather events re- and the resulting rainfall. The two seasons are cently. In 2003, tropical cyclone Ami devas- largely controlled by the north to south tated parts of Vanua Levu, Tavueni, and the movements of the South Pacific Convergence islands in the Lau Group. Heavy rain associ- Baseline Climatology of Viti Levu . Mataki et al. 51 Figure 1. The Fiji Islands showing location of Nadi and Suva sites on Viti Levu. ated with the cyclone brought widespread water and millions of dollars worth of dam- floods in Vanua Levu and other parts of the age. In 1998 western Viti Levu, northern Va- country. Floods of rare magnitude such as nua Levu, and islands in eastern Fiji suffered a one in the summer of 2000 occurred in west- severe drought that almost crippled the sugar ern Viti Levu leaving many homes under industry, stressing moisture-reliant and non- 52 PACIFIC SCIENCE . January 2006 heat-tolerant flora and fauna, resulting in loss in Namaka in Nadi (17.75 S, 177.45 E) and of biodiversity. The cost to the central gov- at Laucala Bay in Suva (18.09 S, 178.27 E) ernment for relief and recovery, such as food can be considered generally representative to and water, fertilizers, cane seeds, etc., was within 10 km of the two sites considered in hundreds of millions of dollars. this study. However, until now only fragmented The daily temperature and rainfall data studies on a few meteorological variables for the baseline period from 1961 to 1990 have been done on the climatological details were analyzed to obtain monthly and annual of Nadi and Suva, and no systematic study climatological means (also referred to as on the subject exists as a published document. ‘‘normals’’). Subsequently, a time series anal- A general account of the climate and weather ysis was carried out using the daily data for of Fiji was provided by Derrick (1951) identi- the period 1961 to 2003 to find monthly, sea- fying three classes of regional climate for the sonal, and annual anomalies and to investigate Fiji Islands.