ENSO: an overview
John Chappell
Research School of Earth Sciences, Australian National University

 In 1977, the eminent climatologist H.H. Lamb wrote: “Analysis by A.B. Pittock…of the variations of Australian rainfall during the present century has shown that in the south and the east of the continent it is strongly dependent on the northward penetration of the prevailing westerlies of the southern Ocean and the latitude of the subtropical high pressure maximum. All over eastern Australia, east of the mountains, however, and in the center of the continent, the rainfall is also significantly correlated with an index of the Southern Oscillation, which at least in part expresses a tilt of the circumpolar vortex towards this or that’s sector”.

Implied by Lamb and earlier examined by Bjerknes (1969) is the concept that effects of the Southern Oscillation extend far beyond the tropical realm where it holds primary sway. The phenomenon itself is a see-saw of atmospheric mass involving exchanges of air between eastern and western hemispheres centered in tropical and subtropical latitudes, with centers of action over Indonesia and the tropical Pacific ocean. The Southern Oscillation was identified by Sir Gilbert Walker in the 1920’s and usually represented by a global map of correlation’s of annual pressure anomalies globally against pressure anomaly at Djakarta. Thus the Southern Oscillation Index (SOI) is a measure of the pressure difference between the eastern Pacific high pressure region and the western Pacific-Indian Ocean low pressure region, commonly expresses as the pressure difference between Jakarta and Tahiti, or Darwin and Tahiti. The index fluctuates from year to year and often reverses.

Seemingly random alternations of droughts, floods and fair seasons have long begged for explanation; meteorologists since walker found correlations between floods, droughts and variations of the SOI but it remained for Bjerknes in 1969 to identify interactions of atmosphere and ocean that underlie the oscillation. Most conspicuous is the east-west equatorial circulation of the atmosphere (names the ‘walker circulation’ by Bjerknes), driven by pronounced difference of sea surface temperature (SST) between cool east pacific and the west Pacific warm pool; secondary is the influence of east Pacific SST on the strength of Hadley cell circulation in the winter hemisphere.

Every few years, SST in the east equatorial Pacific ocean becomes warmer and the center of the west Pacific warm pool migrates eastwards that the Walker circulation ceases or reverses and rainfall patterns and atmospheric circulation changes significantly in both tropical and temperate latitude. Times when eastern pacific SST is anomalously warm are referred to as El Nino (named originally from a weak warm current that flows past Peru around Christmas: Nino= the boy child (Christ); the term ENSO=El Nino/Southern Oscillation). Oscillation between El Nino and normal Walker circulation does not occur with clock work regularity but varies considerably in period, intensity and detail. It involves the ocean-atmosphere interactions identified by Bjerknes but the oscillatory processes remained conceptual until fairly recently, when climate models began to emulate ENSO behaviour. The models do not yet predict ENSO events years ahead and the detailed causes of ENSO variability are much debated. Thus owing to its massive socio-economic impacts, meterologic records are searched vigorously for signatures of ENSO forerunner conditions as well as its statistical periodicity.

Satellite imagery has enhanced our knowledge of the anatomy and development of El Nino events, particularly in terms of SST and cloud fields, and with some thirty years of records now available, several major events now are known at a level of detail that was unavailable when Bjerknes examined both the mechanisms and the long arm of ENSO. Thirty years is insufficient to characterise the fluctuations of droughts and floods, however, because variations of longer periodicity than ENSO are recognized in the march of climate-identified, for example, in 100 year records of Australian river flow as drought-dominated and flood-dominated regimes. Hence, efforts are made to extend the instrumental record with historical data and surrogate measures of climate from other sources, including growth bands of trees and corals. The latter at best were only modestly dependable, however, until it was shown that SST and rainfall (or runoff from the land) can be identified convincingly from precise and detailed analyses of trace elements, oxygen isotope ratios and fluorescence in corals. As Bjerknes noted, SST records from key sites would be invaluable for characterising ENSO; thus coral proxies for SST and rainfall, if dependable, will be of considerable importance for ENSO studies. Furthermore, ancient corals can be used to discover whether ENSO behaved the same as now, in epochs when global climates and oceanic temperature and salinity fields were different, a matter likely to be important if greenhouse warming proceeds as expected.

Owing to the variability of ENSO and longer period fluctuation of drought regimes, as well as the intrusion into tropical meteorology of tropical cyclones (whether these interact with ENSO is debated), the proposition that long proxy and historical records have predictive value needs close scrutiny. The historical associations of ENSO, disruption of harvests by floods or droughts, social upheaval and sometimes epidemics, to be discovered from such records, may prove to be more than passingly instructive in future, however; in Australia, the hydrologic and ecological impacts of ENSO are only two of several environmental responses to climatic variability that are far from fully studies.

“Between 1960 and 1975, drought-produced failures or shortfalls of the harvests in India and Soviet central Asia, about four times in each country and about twice in China, have caused such massive purchases of North American grain that the world’s food reserves were run down and in the worst case in 1972 the world price of wheat doubled within a few months; in 1975 another drought cut the total Soviet wheat harvest even more severely, reportedly by more than 30%” (Lamb, 1977). The degree to which ENSO was implicated in those events is unclear but what is certain is that ENSO has and will continue to be an enduring fact of life. The present New Guinean drought and Indonesian fires not only signal the impact of ENSO; they also show that the need to adapt to ENSO is no less now than in the past and may never have been greater.
 
  

Long-period variations in ENSO and the Australian monsoon

R J Wasson
Geography, Australian National University

Early (spring) rains in the Top End, and therefore a long wet season, occur when the Southern Oscillation Index (SOI) is positive in the previous winter. The SOI also correlates strongly with interannual variability of both pre-monsoon and monsoon rainfall amount. On the Magela Plain, a freshwater swamp in Kakadu N.P., spring rains produce abundant aquatic macrophytes during a La Nina phase of ENSO. When rains begin late, and usually abruptly, aquatic macrophytes are advantaged, under El Nino conditions. Opal phytoliths and sponge spicules are produced during La Nina phases from aquatic grasses. Diatoms are produced during macrophyte periods. Periods of aquatic grass dominance have occurred at 1300+40 AD and 610+80 AD, during which time it is believed La Nina episodes were more frequent. The record of the last 2000 years records two such events, and the modern ‘natural’ trend may be toward another such event.
 
  

Large-scale modes of variability in global climatic data

Robert J. Allan
Climate Impact Group, CSIRO Division of Atmospheric Research
Aspendale, Victoria

A more complete picture of the spatiotemporal nature and structure of the El Nino Southern Oscillation (ENSO) phenomenon is examined using new versions of the historical Global sea-Ice and Sea Surface Temperature (GISST) and Global Mean Sea Level Pressure (GMSLP) data sets in joint Empirical Orthogonal Function (SVD) fractional variance spectra. Preliminary results have isolated four spectral bands at 2-2.5, 2.5-7, 11-13 and 15-20 years that carry ENSO or ENSO like patterns in joint bandpass filtered GISST and GMSLP fields. The 2-2.5 and 2.5-7 year bands are the quasibiennial and ‘classical’ ENSO signals respectively, while the 11-13 year band displays a quasidecadal ENSO like pattern with the warmest sea surface temperatures (SSTs) displaced into the central-western equatorial Pacific in the current Nino 4 area, and the 15-20 year band also has an ENSO like signature as a bidecadal signal with the warmest Pacific SSTs displaced slightly into the Southern Hemisphere but back against the South American coast in something like the contemporary Nino 1+2 and 3 region configuration. There are also indications of fluctuations in the SST patterns over the Indian Ocean basin between quasidecadal and bidecadal time scales, and in conjunction with the 2-2.5 and 2.5-7 year signals may go a long way to explaining Indian Ocean SST dipole patterns. Further work is needed on these decadal to multidecadal signals, but the ‘classical’ definition of ENSO as solely a 2-7 year phenomenon must be seriously examined in light of the resolution of ENSO like patterns on quasidecadal and bidecadal time scales.

This analysis has also looked at lower frequency multidecadal to secular signals in lowpass filtered (29 years) joint LF EOF analyses of GISST and GMSLP. These LF EOFs reveal three dominant modes; a global warming tend pattern, the Sahelian rainfall/interhemispheric temperature contrast signal, and a 20-35 year ENSO like pattern. Interestingly, the global warming trend pattern has neutral to more La Nina-like characteristics across the equatorial Pacific and does not carry an enhanced EL Nino signal as some recent work suggest in an explanation for the past 1970s change in climate over the Pacific Ocean, and the 1990s nature of El Nino events. Such findings have important implications for the question of changes in ENSO under enhanced greenhouse conditions.

*This research is part of an ongoing collaborative study involving Dr Chris Folland and Dr David Parker (Hadley Centre for Climate Prediction and Research, United Kingdom Meteorological Office), Dr Mike Mann (Department of Geosciences, University of Massachusetts) and Dr Ian Smith (CSIRO Division of Atmospheric Research).
 
  

Reconstructing the oceanic and atmospheric components of the ENSO with corals

Mike Gagan
 Research School of Earth Sciences, The Australian National University

 One of the most promising new developments in tropical palaeoceanography involves the precise measurement of Sr/Ca and 180/160 in coral skeletons to reconstruct sea-surface temperature and make inferences about the surface-ocean hydrologic balance. To demonstrate the utility of this technique, we will present coral records for several oceanic settings in the Indonesian-Australian region to reconstruct the evolution of the prolonged El Nino-Southern Oscillation (ENSO) event of 1991-94. We have also applied a multi-tracer approach to fossil corals living from ~5,000-6,000 years ago in the Great Barrier Reef and Indonesia to look for oceanic and atmospheric evidence of individual ENSO events. The early results suggest that parts of the mid-Holocene were marked by warmer SSTs, less (but dependable) monsoonal rainfall, and possibly a weaker ENSO. The persistence in time of the apparent weakening of the mid-Holocene ENSO is unknown, but, if real, the ramifications this weakening should be evident in high-resolution palaeoclimate records throughout much of the tropics.
 
  

Archaeological perspectives on late prehistoric
El Nino events in the Moche Valley, Peru

Ian Farrington
Archeology, Australian National University

El Nino, a Peruvian term, to describe the tropical rains and warm seas which come around Christmas time every few years has been evident as active on the Peruvian coast for several thusand years. It is a phenomenon which brings about completely contrasting conditions to this rainless desert during the rest of the time. The practice of irrigation agriculture is disrupted by these events which do not necessarily bring about widespread devastation and to which the normal response has been  to simply rebuild the destriyed infrastructure and start again.  This paper shall evaluate some archaeological evidence for El Nino's of the past and human responses from the North Coast of Peru, in particular it will describe one rebuild of an aqueduct which received a human sacrifice exactly in its middle to avoid such destruction again.
 
  

The coral record of sea surface temperatures from the Great Barrier Reef

Malcolm McCulloch, Chantal Alibert, John Marshall, and Graham Mortimer
Research School of Earth Sciences, Australian National University

Massive Porites  corals can live for up to 300-500 years, and preserve  within their carbonate skeleton a continuous record of the ambient sea  surface temperature (SST).  Stochiometric trace element constituents of the  aragonitic coral skeleton have temperature dependent seawater/coral  partition coefficients which provide a first order proxy for SST.  Here we  report measurements of high precision Sr/Ca ratios in modern Porites coral  from Davies and Myrmidon in the central Great Barrier Reef (GBR).  At both  Davies and Myrmidon Reefs comparisons of modern coral Sr/Ca ratios with  instrumental SST data from several colonies as well as between reefs  indicates a reproducibility of generally better than B10.5oC.  A 30 year  high resolution Sr/Ca record from Davies Reef clearly shows the cooler  winters which predate the mature phase of El Ninos in 1965, 1972 and  1982-83.  The mean Sr/Ca temperatures also show a pronounced increase of  ~1.3oC, mainly since 1979.  This warming is consistent with, but of larger  amplitude than the overall increase in land-ocean temperatures of the  Southern Hemisphere (~0.4oC), the latter often being attributed to  Greenhouse warming.  It will be shown how longer, multi-century, high  resolution records of this type have the potential of better constraining  the frequency and character of El Nino events as well as providing limits  on the magnitude of natural climate variability on decadal, century and  thousand year time scales.
  

El Niño and drought in Papua New Guinea: an oxygen-isotope and Sr/Ca record of a Porites coral

 Linda K. Ayliffe
Research School of Earth Sciences, The Australian National University

 Rainfall patterns in the tropical western Pacific are thought to be related to the phases of the El Niño Southern Oscillation (ENSO) but instrumental records are of insufficient length to reveal the longer time-scale variations in this climate system. Long-term records of climate preserved in the aragonitic skeleton of corals have the potential to contribute greatly to our understanding of oceanic and atmospheric responses to ENSO.

The manifestations of ENSO in the western Pacific include: (a) a cooling of large areas of the western Pacific as the centre of ocean surface heating moves to the central equatorial Pacific; (b) blocking and weakening of the northwest monsoon in summer; and (c) weakening or reversal of the southeast tradewinds in the western Pacific. Winter droughts and hard frosts in the highlands of Papua New Guinea (PNG) are due, in part, to the lack of orographic rainfall when the tradewinds are weak.

The most comprehensive reconstruction of ENSO events would include information on all three of these climate manifestations. Corals growing offshore from the Sepik River in PNG are well situated to record the oceanic and atmospheric responses to ENSO. In this pilot study we explore the potential of combined oxygen-isotope and Sr/Ca measurements for a Porites coral from this location to accurately record changes in sea-surface temperatures (SST) and rainfall accompanying the onset of ENSO. A 35cm high Porites coral from Blup Blup Island (lat 03’ 30.9' S; long 144o 35.47' E), 30 km from the mouth of the Sepik River and lying in the path of the flood plume, was collected from 3.2m water depth in September, 1996. 1133 micro-samples were taken at 200 µm thickness down the central growth axis of the coral and Sr/Ca and oxygen-isotopes determined. A chronology was established for the upper section of the coral (1982-1996) by comparing the temperatures deduced from Sr/Ca measurements with those recorded by satellite. Using this chronology, oxygen-isotope residuals (Dd18O; oxygen-isotope data corrected for a temperature effect) are found to correlate with river discharge and satellite-based estimates of precipitable water.The Dd18O data reflects the bimodal nature of rainfall in PNG in "normal" non-ENSO years.

The coral record is able to clearly resolve summer monsoonal rainfall from winter southeast trade-wind rainfall events during non-ENSO years.  In addition to an ocean surface cooling of between 0.5 - 1.0 °C during the El Niño events of '82-'83, '87 and '92-'94 indicated by the Sr/Ca data, large anomalies are observed in the coral d18O values at these times. Discharge from the Sepik and neighbouring Ramu Rivers appears to have been dramatically reduced during El Niño events. Both the winter south-east trade wind precipitation peak and the preceding summer monsoonal rains were either absent or considerably diminished at these times.

 We have been able to accurately fingerprint three climatic manifestations of ENSO using the d18O and Sr/Ca signatures preserved in a Papua New Guinean coral skeleton. These results bode well for the reconstruction of ENSO events on longer time-scales using corals from similar locations
 
 

J.C.G Banks
Department of Forestry, SRMES, Australian National Univeristy

Tree rings are a natural storehouse of environmental information from which elements of past climates can be extracted. The principle challenge is to identify species which have strong climate signals in their annual growth rings and hence minimal noise. Historically dendroclimatology began early this century in USA with the search for relationships between sun spot activity and climate using tree rings as a proxy for climate as climate data was limited. Modern studies pioneered by Fritts (1976) and others working out of the Tree-ring Laboratory at Tuscon have greatly expanded knowledge on climate/tree ring interactions allowing climate reconstruction to be extended well beyond the written record. Interest in climate change has in recent years hastened tree ring climate studies with a rapid expansion of the number of species studied and their geographic distribution. To date most dendroclimate studies have focussed on the Northern Hemisphere where the greater availability of long-lived tree species and cross-datable dead wood have seen the construction of long tree ring sequences which are ideal for climate study. The Southern Hemisphere lacks the continuity of land mass for developing a circum polar spatial network and has few suitable long-lived species for developing long tree ring chronologies. Australia has an extensive tree flora whose dendrochronological potential remains largely unexplored. Few chronologies exist and in these the climate signal is limited. Careful species and tree selection will provide useful chronologies from which predictions of past climates and the impact of ENSO can be evaluated. Potentially useful species for ENSO study are given in the paper.
 
  

The environmental impact of past ENSO events: example from a remote oceanic Chilean island

Dr Simon Haberle
Department of Archaeology and Natural History
 Research School of Pacific and Asian Studies

Despite the devastating impact that flooding, drought and fire associated  with El Nino events have had on plant communities in recent times, there is  little information on the long-term persistence of these events or their  consequences on plant communities.  Humans have also played a major part in  altering the nature and distribution of vegetation communities on a global  scale, particularly through forest clearance and the use of fire.  What is  the role of short-term climate variability versus human activity in shaping  our environment?    The islands of the Pacific present an ideal arena in which to investigate  this question. One example is presented from a remote island 700 km west of  Santiago, Chile.  Basal sediments from peat deposits lying close to the  treeline (900 m) on the island of Alexander Selkirk have been AMS dated to 4960 160 yr B.P. The high resolution pollen and  charcoal record shows the earliest subalpine vegetation community was  dominated by Dicksonia, Blechnum and Empetrum with no evidence of fire  until the arrival of human some 400 years ago.  The data implies that  blanket peat formed only after the establishment of modern Pacific Basin  climate system some 5000 years ago.
 

Neville Nicholls
Bureau of Meteorlogy Research Centre
PO Box 1289K, Melbourne, 3001 Australia

I will describe the characteristics of the El Nino-Southern Oscillation that produce the spatial and temporal patterns of climate in the areas it affects. These characteristics are described in “The El Nino-Southern Oscillation and Australian vegetation”, Vegetatio, 91, 23-36, and “Australian rainfall variability and change”, Weather, 52, 66-72. These characteristics are: synchronous climate anomalies (teleconnections), amplified climate variability, one-year duration, phase-locked to annual cycle, and a weak biennial cycle. Paleoclimatic and historical studies of the El Nino-Southern Oscillation need to take these characteristics into account. I will also discuss how interactions between humans, wildlife and the El Nino-Southern Oscillation can lead to major, long-term and possibly unpredictable change, even though the El Nino-Southern Oscillation operates on short time-scales. This is also discussed in the Vegetatio paper. I will also discuss evidence for recent changes in the El Nino-Southern Oscillation and its influence on Australian (“Recent apparent changes in relationships between the El Nino-Southern Oscillation and Australian rainfall and temperature”, Geophys, Res.Letts.,23,3357-3360).
 

Is SOI a good predictor of rainfall in eastern Australia?

Don Poskitt and Ross Cunningham
Department of Statistics and Econometrics and Statistical Consulting Unit of the Graduate School
Australian National University

In this paper we examine the relationship between rainfall and SOI in  three locations in eastern Australia, for monthly data over the period 1876  to 1997. We do  this by constructing a statistical model in which observed  variations in rainfall are accounted for by current and past oscillations  in the SOI. We conclude that there is a statistically significant (p<0.001)  and positive relationship between rainfall and SOI. However, the practical  significance of this relationship is called into question since it appears  to be the case that we cannot say anything precise about variations in  rainfall from one month to the next given particular values of SOI.
 
  

Climatic change and colonial expansion:  The  El Nino/Southern Oscillation  in the Indo-Pacific ocean region and  the  economic and  social history of South and Southeast Asia and the tropics 1200-1800

Richard Grove
 Institute of Advanced Studies,  Global Environmental History Unit RSSS
 Australian National University

Recent research has begun to show that the era of European colonial expansion was coincident with  periods of very clearly defined climatic stress between about 1200 and 1900, and particularly during the seventeenth and eighteenth centuries.    In some parts of the tropics this phenomenon was reflected in a series of unusually severe droughts and other extreme weather events in,  for example,  South-east Asia, South Asia, Southern  and Central Africa and Mexico.  The majority of these droughts were associated with events of the El Nino-Southern Oscillation (ENSO), and with connected failures of the Southeast Asian and South Asian monsoons.  Until now economic historians of the tropics have not had access to any reliable data on the patterns of  ENSO phenomena, even though some more observant writers have suggested that climatic or ecological stresses might help to account for what historians have, for example, termed the 'Seventeenth century crisis', in both Europe and Asia.  The chronology and causality of what have been other hitherto unexplained major historical crises, such as the earliest periods of  decline of Great Zimbabwe, population collapses in Mexico and Java and the historical incidence of famines in India can now  be at least partially explained by what we are now learning about the ENSO phenomenon.  Since ENSO has a characteristically global footprint or pattern of impact (so that,  for example,  severe droughts occur simultaneously, or nearly so,  in Mexico,  Northeast Brazil, India and Australia) the economic historian can acquire useful insights in understanding the relationship between economic crises in one part of the world and economic crises in another,  where causal or systematic links could not previously be made.

The South Asian context is particularly important in this emerging field of study since the archival records are particularly rich, just as they are, for example,  in colonial Latin America and Southern China.  One initial finding of this new field of research appears to indicate that it was at precisely the time that the European powers strengthened their commercial and revenue grip on Asia,  that  the stress of increasingly severe climatic and associated disease and famine events started to impact on agricultural societies, especially between about 1590 and 1800.  Did  these stresses facilitate European expansion?  This paper surveys the evidence for what one may, for convenience and expedience call a  'Drought Age'  by setting it in the context of earlier climatic periods  and by inspecting the evidence for its global character. The paper also focuses on the impact of several of the most severe climatic episodes and suggests that an understanding of their economic and social consequences are especially important in the wider picture of the history of colonial expansion in a global sense. To date the influence of ENSO episodes on economic history has not previously been investigated in any profound way and the need for further archival research is a major preoccupation  and conclusion of this paper.

The prime difficulty in reconstructing ENSO events is the availability of discrete instrumental weather data, as opposed to  data derived from more impressionistic or indirect sources, which although often surprisingly useful (especially where revenue figures, river flows or crop production totals or prices are concerned) has obvious limitations.  The current ENSO event and the experience of the 1972 and 1982-1983 events have tempted some observers to suggest that global warming has given rise to an increased frequency and intensity of the ENSO phenomenon. I suggest here that the historical record, especially from South Asia, but also in  evidence of linked events in Europe and other partrs of the world shows that several  ENSO events  prior to 1877-1879 (normally thought of as the first major ENSO event recorded in a modern instrumental way) were at least as intense, prolonged and widespread as major ENSOs since 1970. The indications for this are already clear, in fact, from the way of Quinn, but recent research on South and Southeast Asian climate history confirms the strength of probable (and sometimes closely-linked or multiple) ENSO events  in, for example,  1251,   1316-1317,  1396, 1405,  1630-1631,  1686-1688,  1737 and 1788-1793.
 
  

The impact of the 1997 drought and frosts in PNG

R. Michael Bourke
Department of Human Geography, Research School of Pacific and Asian Studies
The Australian National University

During most of 1997, much of Papua New Guinea was affected by a severe  drought, arguably the most severe this century. High altitude locations  were affected by repeated frosts between May and November.  Here, an  overview is given of the impact of the drought and frosts on village food  and water supply, health, the PNG economy, migration, urban water supply and  power generation.
 
  

ENSO in PNG: a comparison with earlier ENSOs

Bryant J Allen
Senior Fellow - Department of Human Geography,
Research School of Pacific and Asian Studies,  The Australian National  University

The impact of the 1997-98 ENSO event in PNG has been described in the media  as "the worst ever" or the "one hundred year event". The longest running  quantitative measure of ENSO is the SOI, the difference in air pressure  between Darwin and Tahiti. But it is immediately apparent that the raw SOI  is not a good indicator of impacts in PNG. The last major ENSO, as measured  by SOI anomalies occurred in 1981-82 and its impact in PNG was much less  impressive than 1997-98. The SOI is examined for major ENSO years back to  1896 against rainfall records and qualitative reports from PNG to see if it  is possible to distinguish those patterns in the SOI that are associated  with high impacts in PNG, and those that are not.
 
  

The other side of the island
ENSO related drought and famine in Irian Jaya

Chris Ballard
Resource Management in Asia Pacific Project, Division of Pacific and Asian History
Research School of Pacific and Asian Studies, Australian National University

The Indonesian province of Irian Jaya occupies an unusual position - midway between Asia and the Pacific, the most distant province from Jakarta, and largely inaccessible to media and researchers since the 1960s.  By contrast, neighbouring Papua New Guinea, the other half of the island of New Guinea, is accessible, well-researched and relatively well-covered by a national and international media.

There is some evidence to suggest that the climatic effects of the 1997/98 ENSO event have not been as severe in Irian Jaya as in Papua New Guinea, or even on other islands in Indonesia;  yet the total of 673 drought-related deaths reported for Irian by January 1998 is greater than that for the rest of Indonesia put together, and exceeds the total reported for Papua New Guinea.

Based on field surveys between July and December of 1997, this paper reviews the nature and distribution of the climatic effects in Irian Jaya of the 1997/98 ENSO event, before describing some of the impacts on environment and society in the province.  In many respects, the civil infrastructure of Irian Jaya resembles that of Papua New Guinea in the 1960s, and it is thus instructive to consider how some of the lessons learnt in Papua New Guinea over the past 30 years might be imported and applied to the Irian case.