The Development of Composite Temperature Records

625

426

Trends in extreme daily temperature and rainfall have been analysed from 1961 to 1998 for Southeast Asia and the South Pacific. This 38-year period was chosen to optimize data availability across the region. Using high-quality data from 91 stations in 15 countries, significant increases were detected in the annual number of hot days and warm nights, with significant decreases in the annual number of cool days and cold nights. These trends in extreme temperatures showed considerable consistency across the region. Extreme rainfall trends were generally less spatially coherent than were those for extreme temperature. The number of rain days (with at least 2 mm of rain) has decreased significantly throughout Southeast Asia and the western and central South Pacific, but increased in the north of French Polynesia, in Fiji, and at some stations in Australia. The proportion of annual rainfall from extreme events has increased at a majority of stations. The frequency of extreme rainfall events has declined at most stations (but not significantly), although significant increases were detected in French Polynesia. Trends in the average intensity of the wettest rainfall events each year were generally weak and not significant.

Section: Quality Controlmentioning

confidence: 99%

Trends in extreme daily rainfall and temperature in Southeast Asia and the South Pacific: 1961–1998

Manton

Della-Marta

Haylock

et al. 2001

625

426

“…Discontinuities in climate records can result from changes to the station or its operation, e.g. changes in site location, observation practice, exposure, or instrumentation, and can affect both the mean and extremes of a climatic distribution (Trewin and Trevitt, 1996). In conclusion, a set of 89 stations (Appendix A and Figure 2) was used in the analysis, including the 20 urbanized records (identified in Table II).…”

Section: Climate Station Selection and Urbanization Issuesmentioning

confidence: 99%

Change in mean temperature as a predictor of extreme temperature change in the Asia–Pacific region

Griffiths

Chambers

Haylock

et al. 2005

215

156

Trends (1961Trends ( -2003 in daily maximum and minimum temperatures, extremes and variance were found to be spatially coherent across the Asia-Pacific region. The majority of stations exhibited significant trends: increases in mean maximum and mean minimum temperature, decreases in cold nights and cool days, and increases in warm nights. No station showed a significant increase in cold days or cold nights, but a few sites showed significant decreases in hot days and warm nights. Significant decreases were observed in both maximum and minimum temperature standard deviation in China, Korea and some stations in Japan (probably reflecting urbanization effects), but also for some Thailand and coastal Australian sites. The South Pacific convergence zone (SPCZ) region between Fiji and the Solomon Islands showed a significant increase in maximum temperature variability.Correlations between mean temperature and the frequency of extreme temperatures were strongest in the tropical Pacific Ocean from French Polynesia to Papua New Guinea, Malaysia, the Philippines, Thailand and southern Japan. Correlations were weaker at continental or higher latitude locations, which may partly reflect urbanization.For non-urban stations, the dominant distribution change for both maximum and minimum temperature involved a change in the mean, impacting on one or both extremes, with no change in standard deviation. This occurred from French Polynesia to Papua New Guinea (except for maximum temperature changes near the SPCZ), in Malaysia, the Philippines, and several outlying Japanese islands. For urbanized stations the dominant change was a change in the mean and variance, impacting on one or both extremes. This result was particularly evident for minimum temperature.The results presented here, for non-urban tropical and maritime locations in the Asia-Pacific region, support the hypothesis that changes in mean temperature may be used to predict changes in extreme temperatures. At urbanized or higher latitude locations, changes in variance should be incorporated.

“…It is known that applying annual adjustments to all daily data may not create a truly homogeneous daily series. Trewin and Trevitt (1996), testing this type of conventional constant-difference procedure for temperature, argue that there are stations at which a frequency-distribution-based (temperature-dependent) technique for the homogenization of series would perform better. It is likely that the frequency-distribution method would also perform substantially better in any consideration of extreme precipitation events.…”

Section: Changes In Extreme Rainfall Indices Over the 20th Centurymentioning

confidence: 99%

“…The constant-difference adjustment of daily rainfall data by analysis of annual series is sub-optimal (Trewin and Trevitt, 1996;Manton et al, 2001); however, it has been applied here, to minimize the influence of gross inhomogeneities on the results while maximizing the number of stations available across the South Pacific for analysis. Improvements to this homogeneity technique will be incorporated in future work.…”

Section: Changes In Extreme Rainfall Indices Over the 20th Centurymentioning

confidence: 99%

Trends in extreme daily rainfall across the South Pacific and relationship to the South Pacific Convergence Zone

Griffiths

Salinger

Leleu

2003

113

Daily rainfall records from 22 high-quality stations located in the South Pacific were analysed, over the common period 1961-2000, in order to assess whether extreme rainfall events have altered in their frequency or magnitude. A comprehensive spatial coverage across the South Pacific was provided, analysing a range of indices of extreme precipitation, which reflect both high rainfall events and drought. Clear spatial patterns emerged in the trends of extreme rainfall indices, with a major discontinuity across the diagonal section of the South Pacific Convergence Zone (SPCZ).Stations located between 180 and 155°W exhibit a greater number of significant abrupt changes in extreme climate than elsewhere in the South Pacific, and the majority of climatic jumps occur in the 1970s or 1980s (coincident with a displacement northeastward of the diagonal part of the SPCZ and a large local increase in mean annual temperature). Notably, all significant abrupt changes in an extreme rainfall intensity index occurred in the late 1970s or early 1980s, and in every case the index showed an increase in extremity following the change point, regardless of station location. For the stations located south of the SPCZ, this may also be linked to the observed warming since the 1970s. Significant abrupt changes in mean precipitation were also identified around the mid 1940s, for two longer, century-scale records, which again correspond to a major displacement of the diagonal section of the SPCZ.An indicator of the diagonal SPCZ position is significantly temporally correlated with an extreme rainfall intensity index, at two locations either side of the diagonal section of the SPCZ, at decadal time scales or longer. This suggests that the displacement of the diagonal portion of the SPCZ on decadal time scales influences not only mean precipitation, but also daily rainfall extremes.