Blair Trewin

Global observed changes in daily climate extremes of temperature and precipitation

A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near-complete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

On the relationships between the el niño-southern oscillation and Australian land surface temperature

A comprehensive analysis of the linear covariability of Australian surface temperatures with the Southern Oscillation (SO) has been performed. Using newly available data, including high quality observational temperature analyses and the National Centres for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) reanalyses, it is shown that the SO plays a major role in the variability of seasonal maximum, minimum and mean temperature, and diurnal temperature range. The observed relationships are strongest over eastern Australia year round and over northern Australia during the summer half year. The SO–temperature correlations are comparable in magnitude with those described previously for Australian rainfall, but with a strong geographical and seasonal variation. This complexity cautions against the exclusive use of annual means, and has probably led to an underestimation of the importance of the SO for Australian temperature variability in earlier studies. It is shown that SO-related variations in the radiative and latent heat fluxes are largely responsible for the SO–temperature covariability. Variations of the sensible heat flux are primarily forced by changes in the surface temperature, and act to dampen the temperature signal. Variations of the short- and long-wave radiative fluxes tend to have a similar magnitude, but different signs, meaning that the primary radiative signal appears in the diurnal temperature range. The seasonal and spatial variations in radiative and latent heat fluxes are largely responsible for the complexities of the SO–temperature covariability. An analysis of the SO–temperature relationships at lag suggests that variations of Australian temperature associated with the SO are as predictable as those of Australian rainfall. There is evidence that the predictability of temperature is enhanced by variations in large-scale soil moisture, which is associated with SO–rainfall changes. Copyright

Guiding the Creation of A Comprehensive Surface Temperature Resource for Twenty-First-Century Climate Science

Surface temperature data – observed primarily for weather-related purposes – are disparate, originating from ever evolving instrument types and observational practices. Although several global databases are in use internationally, no comprehensive global repository exists and many data are undigitized or restricted. Scientists have painstakingly obtained vast quantities of data, carefully removed random errors and accounted for systematic biases. The 21st Century demands go further - requiring highly detailed (spatially and temporally), globally complete, long-term products, with quantified uncertainties, and created from freely available, fully traceable data. Many decisions of substantial socio-economic importance rely on the accuracy of such products. An international meeting was held to plan how best to facilitate such efforts. A central repository is to be created, where data are traceable from their origins to final product. Strategies are outlined to rescue non-digitized data and move towards entirely freely available data. Creation of multiple methodologically independent products is recommended for quantifying uncertainty. Methods of benchmarking and assessing multiple products to aid inter-comparison and end-user product selection are described. Data-products would be obtained and visualized using in-house tools from the planned data-portal. Structure and governance include engagement with bodies such as WMO and, importantly, with experts other than climatologists.

Changes in the frequency of record temperatures in Australia, 1957-2009

The temporal distribution of record high and low temperatures in Australia during the 1957-2009 period has been investigated. Use has been made of two different data-sets: station data of daily maximum and minimum temperatures at stations drawn from the Australian high-quality daily temperature data-set, and area-averaged anomalies of monthly maximum and minimum temperature for the six Australian States and the Northern Territory. For both data-sets, there is a marked tendency for low temperature records to outnumber high temperature records in the early part of the period, and for high temperature records to outnumber low temperature records in the later part of the period, with the ratio of high to low temperature records mostly being below 0.5 to 1 in the 1957-66 decade and above 2 to 1 in the 1997-2009 period. Time series of the difference between the numbers of high and low temperature records show positive trends significant at the five per cent level for all cases examined. An examination of the frequency of record-setting in area-averaged data, detrended using the observed trends in mean annual Australian maximum and minimum temperatures, suggest that the frequency of record-setting is broadly consistent with the mean annual temperature trend for maximum temperatures, but for minimum temperatures changes in the frequency of record-setting are somewhat smaller than would be expected given the mean annual temperature trend.

Data Rescue in the Southeast Asia and South Pacific Region: Challenges and Opportunities

BY CHER M. PAGE, NEVILLE NICHOLLS, NEIL PLUMMER, BLAIR TREWIN, MIKE MANTON, LISA ALEXANDER, LYNDA E. CHAMBERS, YOUNGEUN CHOI, DEAN A. COLLINS, ASHMITA GOSAI, PAUL DELLA-MARTA, MALCOLM R. HAYLOCK, KASIS INAPE, VICTOIRE LAURENT, LUC MAITREPIERRE, ERWIN E.P. MAKMUR, HIROSHI NAKAMIGAWA, NONGNAT OUPRASITWONG, SIMON MCGREE, JANITA PAHALAD, M.J. SALINGER, LOURDES TIBIG, TRONG D. TRAN, KALIAPAN VEDIAPAN, AND PANMAO ZHAI

Significant decline in storminess over southeast Australia since the late 19th century

Geostrophic wind speeds (geo-winds) were estimated for southeast Australia by constructing eight station triangles from instrumental records of qualitycontrolled sub-daily mean sea-level pressure from 1885 to 2008. Seasonal 95th and 99th percentiles of the geo-winds were calculated and used to identify periods of enhanced ‘storminess’ over each triangle. While the results were marked by strong multi-decadal variations, they indicated a statistically significant decline in storminess across most regions in southeast Australia since the end of the 19th century, particularly in autumn and winter. The results for winter for most regions were also statistically significantly correlated with year-to-year variations in southeast Australian rainfall although the correlation coefficients were small. Regionally averaged results showed a peak in storminess in the 1920s with least activity in the 1960s in all seasons. Although there has generally been an upturn in storminess in recent decades compared to the immediately preceding decades, it has not been of nearly the same magnitude as in the late 19th and early 20th century. While similar studies have been performed in the northern hemisphere over this length of period, we believe that this is the first time that the method has been applied to Australia. The results indicate that in addition to other climatic processes, the long-term decline in storminess may be contributing to the persistent drought conditions that are being experienced in this densely populated region.

A new integrated and homogenized global monthly land surface air temperature dataset for the period since 1900

A new dataset of integrated and homogenized monthly surface air temperature over global land for the period since 1900 [China Meteorological Administration global Land Surface Air Temperature (CMA-LSAT)] is developed. In total, 14 sources have been collected and integrated into the newly developed dataset, including three global (CRUTEM4, GHCN, and BEST), three regional and eight national sources. Duplicate stations are identified, and those with the higher priority are chosen or spliced. Then, a consistency test and a climate outlier test are conducted to ensure that each station series is quality controlled. Next, two steps are adopted to assure the homogeneity of the station series: (1) homogenized station series in existing national datasets (by National Meteorological Services) are directly integrated into the dataset without any changes (50% of all stations), and (2) the inhomogeneities are detected and adjusted for in the remaining data series using a penalized maximal t test (50% of all stations). Based on the dataset, we re-assess the temperature changes in global and regional areas compared with GHCN-V3 and CRUTEM4, as well as the temperature changes during the three periods of 1900–2014, 1979–2014 and 1998–2014. The best estimates of warming trends and there 95% confidence ranges for 1900–2014 are approximately 0.102 ± 0.006 °C/decade for the whole year, and 0.104 ± 0.009, 0.112 ± 0.007, 0.090 ± 0.006, and 0.092 ± 0.007 °C/decade for the DJF (December, January, February), MAM, JJA, and SON seasons, respectively. MAM saw the most significant warming trend in both 1900–2014 and 1979–2014. For an even shorter and more recent period (1998–2014), MAM, JJA and SON show similar warming trends, while DJF shows opposite trends. The results show that the ability of CMA-LAST for describing the global temperature changes is similar with other existing products, while there are some differences when describing regional temperature changes.

WMO assessment of weather and climate mortality extremes : lightning, tropical cyclones, tornadoes, and hail

AbstractA World Meteorological Organization (WMO) Commission for Climatology international panel was convened to examine and assess the available evidence associated with five weather-related mortality extremes: 1) lightning (indirect), 2) lightning (direct), 3) tropical cyclones, 4) tornadoes, and 5) hail. After recommending for acceptance of only events after 1873 (the formation of the predecessor of the WMO), the committee evaluated and accepted the following mortality extremes: 1) “highest mortality (indirect strike) associated with lightning” as the 469 people killed in a lightning-caused oil tank fire in Dronka, Egypt, on 2 November 1994; 2) “highest mortality directly associated with a single lightning flash” as the lightning flash that killed 21 people in a hut in Manica Tribal Trust Lands, Zimbabwe (at time of incident, eastern Rhodesia), on 23 December 1975; 3) “highest mortality associated with a tropical cyclone” as the Bangladesh (at time of incident, East Pakistan) cyclone of 12–13 November ...

Network-derived inhomogeneity in monthly rainfall analyses over western Tasmania

Monthly rainfall in the wetter western half of Tasmania was relatively poorly observed in the early to middle parts of the 20th century, and this causes a marked inhomogeneity in the operational gridded monthly rainfall analyses generated by the Australian Bureau of Meteorology up until the end of 2009. These monthly rainfall analyses were generated for the period 1900 to 2009 in two forms; a national analysis at 0.25° latitude-longitude resolution, and a southeastern Australia regional analysis at 0.1° resolution. For any given month, they used all the monthly data from the standard Bureau rainfall gauge network available in the Australian Data Archive for Meteorology. Since this network has changed markedly since Federation (1901), there is obvious scope for network-derived inhomogeneities in the analyses. In this study, we show that the topography-resolving techniques of the new Australian Water Availability Project analyses, adopted as the official operational analyses from the start of 2010, substantially diminish those inhomogeneities, while using largely the same observation network. One result is an improved characterisation of recent rainfall declines across Tasmania. The new analyses are available at two resolutions, 0.25° and 0.05°.

Documentation and verification of the world extreme wind gust record: 113.3 m s–1 on Barrow Island, Australia, duringpassage of tropical cyclone Olivia

This paper details the event, recording instrumentation, and verification of a new world extreme three-second average wind gust record of 113.3 m s–1, measured on Barrow Island, Australia, during the passage of tropical cyclone Olivia in April 1996, and the public and media reaction to that verification. This record supersedes the previous extreme of 103.3 m s–1 measured at the Mount Washington Observatory in New Hampshire, USA, in April 1934. Members of a World Meteorological Organization evaluation committee critically reviewed the data of the Olivia event, determined the Barrow Island wind measurement was valid and established the record. With the announcement of the record, interesting public reaction has occurred and is discussed, as well as the concept of more detailed classification of wind extremes. Although Olivia now holds the record for having the highest wind gust ever measured, this record doesn’t imply that Olivia is the most intense cyclone recorded. However, planners should be aware that extreme gusts well above the ‘typical’ gusts quoted on the intensity scale are possible for tropical cyclones, particularly for category 4 and 5 tropical cyclones.