Recent Climate History of Hawaii1 Recent Climate History of Hawaii1 Recent Climate History of Hawaii1

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Recent Climate History of Hawaii1

DENNIS NULLET 2

ABSTRACT: The recent energy and synoptic climate ofHawaii is examined inin this article. The results indicate trends in the energy climate, climate, increasing tempera ture and decreasing solar radiation, though no evidence is found of trends or cycles in the synoptic climatic elements, elements, rainfall and sea level pressure.pressure.

THIS ARTICLE PRESENTS a brief discussion and value is one of the highest annual rainfall analysis of the climate in Hawaii since scienti totals ever recorded in Honolulu. Mean baro fic weather observations began in the nine metric pressure was 1015mb (29(29.973.973 in. mer teenth century. cury) during his stay, near the long-term long-term mean for September through April of 1016 mb. mb. Sea surface temperatures averaged 26.426.4°C°C (79SF), which, if accurate, would be un WEATHER OBSERVATIONS usually warm (Wilkes (Wilkes 1851). Some of the earliest meteorological obser- In the late nineteenth century, weather ob- vations in Hawaiiwere reported by LtLt.. Char- servations became more common asagricul les Wilkes, who, while in command ofthe U.S. U.S. tural interests grewgrew,, and finally the newly Exploring Expedition,Expedition, spent the winter of established Climatological Office for the then 1840-18411840-1841 in the islands. islands . Wilkes' visit to the Territory ofHawaii began publishing records islands, just 62 years after their discovery by in 1905. By 1985nearly 2000 climatological Captain Cook, appears tohave coincided with stations had been established and maintained blustery weather. He found thedaytime winds at one time or another, giving Hawaii one of "blow with great strength" though "the nights the densest climate monitoring networks in are calm and beautiful" (Wilkes 1851). 1851). Wilkes the world (Giambelluca et al. 1986). added a postscript to his assessment of the To illustrate the history of the general elicli nocturnal weather, however. On an expedi- mate during this century, weather data are tion to the summit of Mauna Loa,Loa, Wilkes' graphed in Figures 1I and 2. 2. The data are party measured 457 mm (18 in.)of snow, ex- separated into climatic elements related to the perienced gales from the southwest gusting up energy balance, radiation and temperature, and to 21 m/sec m/sec (47 mph), mph) , and recorded tempera- climate elements that indicate synoptic condi tures as low as - 7.8°C (18(1 8°F).°F). On huddling in tions, tions, rainfall and sea level pressure. The air camp near the summit, WilkeWilkess later wrotewrote,, temperature curve was compiled by taking the "the howling wind ...... rendered the hours of average of three windward sites at Lihue, darkness truly awful" awful" (Wilkes 1970)1970).. Kauai (State ID: ID : 1020.1,1020.1, National Oceanic Wilkes reported the mean annual tempera- and Atmospheric Administration (NOAA) ture at Honolulu to be 2424.3°C.3°C (75.8°F)(75.8°F) based ID: ID: 5580);5580); Hana, Maui (State ID: 355.0; 355.0; --- onon-s-everal-years--of-measuremen-several years "ofmeasurements,"nearts;-n-eactlre- the - NOAAID:1125)N

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FIGURE 1.1. Historical energy climate. climate. DataDa ta are discussed in the text. The reciprocal relationship between temperature and radiation may indicate that cloudiness acts as a negative feedback agent to temperature fluctuations in the north central Pacific. (0 symbols indicate ggloballoba l radiationradiation and air temperaturetemperature.. '"6. symbols indicate sea surface temperaturetemperature.).)

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FIGURE 22.. Historical synoptic climate indicators.indicators. Data are discussed in the texttext.. Cycles and trends appear absenabsentt in the data, altalthoughhough rainfall variations are generagenerallylly in phase at the lleeward,eeward, windward, and intermediate sitessites.. 98 PACIFIC SCIENCE, Volume 43, January 1989

iods.iods. Accordingly, the following corrections however. Infact, 18001800-1850-1850 was a time of were applied to the post-1950 airport records:records : maxima in AAlpinelpine glaciation and Icelandic sea Lihue: -0.6°C, - 0.6°C, Hana: -0.2°C,- 0.2°C, Hilo, ++0.1°C.0.1"C. ice (Lamb 1977). Possible sources of variation in these records The cause ofthe temperature trend is largelarge are discussed discussed by Hoyt and Siquig (1982). The ly a matter of speculationspeculation.. Possible explanaexplana sea surfacesurface temperaturetemperature (SST) curve has been tions might be a change in atmospheric circu derived from weekly sea surfacesurface temperature lation or warming by greenhouse gases, such measurements collected offKoko Head, Oahu.Oahu. as carbon dioxide and methanemethane.. Wentworth These data are discussed in Seckel and Young (1949) reported a significant easterly shift ill"in (1977).(1977). Solar radiationradiation has been measured measured in the tradewinds over Hawaiian waters between Honolulu since 1932, 1932, first at the Hawaiian 1910 and1940 followed by a return to more Sugar Planters'Planters' Association's Makaki Substa northerly winds through 1946,corresponding tiontion (StateID: ID:707.0), 707.0), and, since 1976, at the nicely to the temperature curvecurve.. An analysis of University ofHawaii (these data are discussed local winds since 1946 shows no continuation by Ekern 1982). 1982). The rainfall data (from of this trend, but a study of winds over the Lihue,Lihue, Hilo, and Honolulu;Honolulu; State ID: 703.0; 703.0; entire Pacific Ocean (Whysall et al. 1987)indi1987) indi NOAA ID: 1919) and sea level pressure data cates a slight easterly shift in the tradewinds (from(from Honolulu) have been smoothed by cal over thepast 30years. years. An easterly shift in the culating 5-year running mean values; that is,is, tradewinds would increase the southerly a value plotted for a given yearyear represents the component of the North Equatorial Current average of that year'syear's measurements plus the and bring warm equatorial water into the twotwo previousand two successive year's year' s mea region.region . Seasonal cycles in the North EquaEqua surementssurements (data from NOAA'sNOAA's ClimatologiClimatologi torial Current and associated forcing mech calcal Data forforthe States and the World Meteo anisms are discussed by Wyrtki (1974) and rologicalrological Organization'sOrganization's World Weather White(1977), though no trends are evident Records).Records). The quality of the rainfall datadata are between 1950 and 1970. Namias (1969), how discusseddiscussed by Giambelluca et al. (1986). ever, reported warmer than normal SSTs for much of the north-central Pacific between 1954 and 1967. This study also suggests an THE ENERGY ENERGYCLIMATE CLIMATE abrupt increasein SST in the fall of 19611961,, Climatic time series data are generally anal- anal - associatedassociated with an anomalously strong north yzed by looking for trends and cycles cycles in the Pacific high-pressure ridge. This jump corres individualindividual climatic elements and for relation-relation- ponds closelywith the temperature data given shipsshipsbetween these elements. elements. An analysis of in Figure 1. I. thethe recentenergy climate depicted in Figure 1IAs another possible mechanism for the obob isis particularly interesting. Air temperatures served warming trend in HawaiiHawaii,, it is particu rose from the the beginning of the century until larly appropriate to consconsiderider greenhouse gasgas about 1940, declined to 1955, and then re- re- es inlight of the importance of Mauna Loa sumed the upward trend. In support of the Observatory in documenting the steady rise in recentrecent warming trend,trend, sea surfacesurface tempera- atmospheric carbon dioxide. Although thethe tures,tures , takentakenoff Koko Head,Head , Oahu,Oahu, have risen magnitude of the overall temperature increase - aboutO.4aboutO.4~CsinceJ955._Ihe~C since 1955.The10caLtemperature_sincelocal.temperature.Lsince ___.1908_exceeds_mosL_predictions1908 ~exceeds _ mosL_predictions____ for recordrecord matches global temperature trends ex- carbon dioxide-induced warmingwarming,, increased cept for the period of 1955-19751955-1975 when global longwave radiation trapping likely contributes temperaturestemperatures remainedremainedfairly constant (Jones to thetrend. et al. 1986). 1986).The few years of temperature data In opposition to the temperature trendtrend,, reported by Wilkes indicate a warmer period measured solar radiation in Honolulu rose ininthe the 1830s.This is supported in part by the until the mid-1950s and has since declined by apparent high measured SST.SST. Global temper-temper- nearly 0.5% per yearyear.. The general shape of the atures of the period were markedly lower,lower, radiation curve is supported by solar radia- Recent History of Hawaii's Climate-Climate-NuLLNULLETET 99

tion measurements at Mauna Loa Observa- atmospheric pressure, show no apparent tory and by many agricultural solar radiation trends in the record. A time series analysis stations throughout the state. state . Hours ofbright reveals that strong cyclic patterns are also sunshine [which has been usedin other climate absentabsent.. The aapparentpparent absence of trends and history analyses (Angell et al. 1984,Changnon cycles in the record makes the job of the 1981)], recorded at Honolulu Airport since weatherperson, who is called upon to predict 1905,1905, also support the long-term solar radia- tomorrow's weather, or even next year's, tiontrend. trend . These corroborating datadat a indicate doubly difficult. Recent efforts at weather that the observed trend has not been confined prediction have moved away from searching to the Honolulu site, but is a statewide for cycles andhave concentrated on global phenomenon. weather eventsevents,, such as EIEl NinoNifio,, as precur- The observation that the radiation trend in sors to Hawaiian weather patterns.patterns. Hawaii tends to oppose the temperature trend The smoothed rainfall records for a wind has important implications for global climatic ward (Hilo), (Hilo), leeward (Honolulu),(Honolulu), and inter change. A major question in climatology to- mediate (Lihue) site generally fluctuate about day is whether temperature increases due to the mean in phase,phase, particularlyparticularly for Lihue and greenhouse gases will be offset by feedback Honolulu. This suggests common mechanisms mechanisms.mechanisms. It has been suggested that the for variation,variation, such as the frequency of fronts Earth might maintain thermeostasis, or con- and upper troughs in winter. Although the stant temperature, by regulating its solar amplitude of yearly fluctuations in rainfall is energy receipt through changes in cloud cover greatest at thewet windward ssite,ite,as a percent (Charlson et al.1987). 1987). Since clouds are highly age ofthe average valuevalue,, variability is greater reflectiveof solar radiationradiation,, an increase inat the drier ssites.ites. The coefficient of variation cloud cover would reducethe solar energy for annual totals of rainfall at Honolulu is absorbed by the Earth,Earth, which would pre presum-sum- 35%, 35% , at Lihue 25%25%,, and at Hilo 21%.21 %. RainRain ably have a cooling effect. effect. In Hawaii,Hawaii , as trends fall is one of the most variable climate ele in atmospheric transmissivity have not bebeenen mentsments.. By contrastcontrast,, the coefficient ofvariation reported (Mendonca et al. 1978),the recent for the annual Honolulu solar radiation totals decreasein solar radiation at the ssurfaceurface must is just 5%5%,, for temperatures at Hilo, Hilo, LihueLihue,, be due to an increase in average cloud cover. Hana, and Honolulu is between 2% and 33.5%,.5% , This suggests that, in the Hawaiian Islands andfor summer and winter sea level pressure area at least, cloud cover doesindeed appear isless than 0.2%0.2%.. to increase in a warmer atmosphere andthus The mean in annual rainfall appears stable may act as a negativefeedback agent to tem-for allthree stations, an indication that long perature fluctuationsfluctuations.. Similar observations term trends are absent for Hawaiian rainfall. have been reported for EuropeEurope,, India,India, and the In a similar analysis using many morerainfall United States (Henderson-Sellers 1987). Of stations around the state, state , Woodcock and course, it is possible that the temperature and Jones(1970) (1970)foundfound evidence ofofaa slight, though radiation trends are unrelated;unrelated; the decrease in not statistically significant, decline in rainfall solar radiation could be due to a change in between 1910 and 19601960.. Despite the absence global circulation patterns, for exampleexample.. Or ofstrong rainfall trends, it has been noted that ..-- -the-increase-in-temperature-the increase in.temperature could-becould.be a.delayed---drought-a delayed.; drought yearsyeal'stend-tobe-cluster tend-to beclustered. thermal lag response to high solar radiation in As with rainfall, rainfall , sea level atmospheric pres-pres- the middle of the century. sure levels fluctuate evenly about a steady mean value. The variation in January pres sures, subject to winter storms and pressure troughs, is much greater than in July when a SYNOPTIC WEATHER INDICATORSINDICATORS strong Pacific high-pressure cell is established Unlike the energy climate elements,elements, the to the north and tradewinds dominatedominate.. It is synoptic weather indicatorsindicators,, rainfalland interesting tonote that the dips and peaks in 100 PACIFIC SCIENCE, Volume 43, 43, January 1989

January and pressure generally oppose annual LITERATURE CITED rainfall atHilo. Hilo . ANGELL, J. K., JJ.. KORSHOVER, and G.G . F.F. COT TON. 1984.1984. Variations in United States clouds and sunshine, 1950-1982. J. CliCli- CONCLUSIONS matol. Appl. Meteorol. 23: 752752-767.-767. CHANGNON, S. A. 1981. Midwestern cloud, Since Wilkes' visit to the islands in the mid Since Wilkes' visit to the islands in the mid- sunshine and temperature trends since 1800s the study of Hawaiian weather has 1800s the study of Hawaiian weather has 1901: P~ssible evidence for jet contrail grow~ enormously. The network of clima~e grow~ enormously. The network of clima~e effectseffects.. J.Appl. Meteorol. 20:496-508.20: 496-508. stations in the islands is one of the densest III stations in the islands is one of the densest m CHARLSON,CHARLSON, R.R. J., J. J. E.E. LOVELOCK, M.M. O.O. AN-AN the world, particularly the rain gauge net the world, particularly the rain gauge net- DREAE, SS.. G.G . WARREN.WARREN. 1987. Oceanic phy-phy work. This reflects the importance ofweather work. This reflects the importance ofweather toplankton, atmospheric sulphur, cloud in the daily life ofmodern Hawaii. The value in the daily life ofmodern Hawaii. The value albedo and climateclimate.. Nature 326: 655-661. 655-661. of local weather measurements can be easily of local weather measurements can be easily EKERN, P. C. 1982. Variation in sunlight inin- illustrated by noting that most of the climate illustrated by noting that most of the climate duced by topography under the tradewind data gathered in Hawaii are collected b~ the data gathered in Hawaii are collected the regime on Oahu, Hawaii.Hawaii. Pages 56-61 iinn private sector, and, in particular, by agricul private sector, and, in particular, by agncul- Conf. Climate Energy: Climatol. AspectsAspects tural concerns. tural concerns. Industr. Oper., Ashville, N.C. An understanding of the past climate may An understanding of the past climate may GIAMBELLUCA,GIAMBELLUCA, T.T. WW.,., MM.. AA.. NULLET, and offer clues to what we might expect in the offer clues to what we might expect in the TT.. A. SCHROEDER. 1986. Rainfall atlas of future. It appears that annual rainfall is not future. It appears that annual rainfall is not Hawaii.Hawaii. Dept. of Land and Natural Re-Re predictable by statistical methods, and thus, predictable by statistical methods, and thus, sources Rept. R76. State of Hawaii, as has happened in the past, the State ~f as has happened in the past, the State Honolulu. Hawaii will be forced to handle drought pen Hawaii will be forced to handle drought pen- HENDERSON-SELLERS, A. 1987. 1987. Climate is a ods in response to, rather than in accurate an ods in response to, rather than in accurate an- cloudy issueissue.. New Scientist 114(1570): 37-3937-39.. even~. Tem:peratur~ ticipation ofof,, the event. Temperatur~ trendstrends HOYT, D. VV.,., and R. AA.. SIQUIG.SIQUIG. 1982. Possible are more clear. The climate IS warmmg. Al are more clear. The climate IS warmmg. Al- influence of volcanic dust veils or changes ~eath though this has little influence on local ~eath- in solar luminoluminositysity on long-termlong-term local er, global warming may affect Hawaii.Hawall. An temperature records.records . J. Atm.Atm. SciSci.. 39: increase in Earth's temperature wouldcause 680680-688.-688. the expansion of seawater and a corre the expansion of seawater and a corre- JONES,JONES, P.P. DD.,., TT.. MM.. L. WIGLEY, and P. B. T~o sponding rise in sea level inin..Hawaii. T~o WRIGHT. 1986. Global temperature variavaria- studies on the phenomena predict a 70-cm nse tionsbetween 1861 and 1984. Nature 322: within the next 4040-100-100 years. Ifthis happens, 430430-434.-434. few near-shore structures will be endangeredendangered,, LAMB, H. H. 19771977.. Climate history and the but Hawaii could face changes in beaches and but Hawaii could face changes in beaches and futurefuture.. Princeton UnivUniv.. Press, Princeton, reefsreefs, increased floodingat the lower reaches NN.J..J. of streams, and a decrease in water quality in of streams, and a decrease in water quality in MENDONCA, B. G., K. J. HANSON,HANSON, and J. JJ.. the lowest-lying areas ofthe aquifer (Moberly the lowest-lying areas ofthe aquifer (Moberly DELUISI. 1978. Volcanically related secular and Mackenzie 1985). trends in atmospheric transmission at Mau-Mau na _..LQL.o...a._D_b_s.e.nraloi)',a_D bsenratoxy,__H.a.waii_S_cienceHawaii. _ Science 2(3): 513-515. 202(3): 513-515. ACKNOWLEDGMENTS MOBERLY, R.,R., and FF.. TT.. MACKENIZE. 1985. Climate change and Hawaii: Significance I would like to thank Sae Kusaka for the and recommendations.recommendations. University of excellent graphs.graphs. I would also like to thank Hawaii Institute ofGeophysics Rept. HIG NOAA-NationalNOAA-National Marine Fisheries Service 85-1. Honolulu, Hawaii. Southwest Fisheries Center in Honolulu for NAMIASNAMIAS,, J.J. 1969.1969. Seasonal interactions be providing the Koko Head SST datadata.. tween the North Pacific Ocean and the

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atmosphere during the 1960s1960s.. Mon. Weath BIGG. 1987. Long-term changes inthe er Rev. Rev . 87: 173-192173-192.. tropical Pacific surface wind field.field. Nature SECKEL, G.G . R,R., and M. Y. YY.. YOUNG.YOUNG. 1977.1977. 327:216-219.327 :216-219. Koko HeadHead,, Oahu, sea surface temperatures WILKES,WILKES, C. 1851. MeteorologyMeteorology.. C. Sherman, and salinities,salinities, 1956-1973,1956-1973, and Christmas Philadelphia. Island sea surface temperatures, 1954-1973.1954-1973. WILKES, C. 1970.1970. Narrative of the United FishFish.. Bull. 7575:: 767-779. States exploring expedition. Vol. IV. Gregg WENTWORTH, C. K. 1949. Directional shift of PressPress,, Upper Saddle River, N.J.N .J. tradewinds at Honolulu. Pac. Sci. Sci. WOODCOCK, A. H., and R. H.H . JONES.JONES. 19701970.. 3(1):87-89.3(1):87-89. Rainfall trends in Hawaii. J. Appl. WHITE, W. B. 1977. 1977. Secular variability in the Meteorol. 9:690-696. 690-696. baroclinic structure of the interior North WYRTKI, K. 1974. Equatorial currents in the Pacific 1950-1970. 1950-1970. JJ.. Marine Res. Pacific1950-1970 1950-1970 and their relation to the 35:35 :587587-607.-607. tradewinds.tradewinds. J. Phys. Ocean. 4: 372372-380.-380. WHYSALL,WHYSALL, K. D. D . B., N. S. COOPER, and G. R .