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.
ABSTRACT:Rainfall records for 23 countries and territories in the western Pacific have been collated for the purpose of examining trends in total and extreme rainfall since 1951. For some countries this is the first time that their data have been included in this type of analysis and for others the number of stations examined is more than twice that available in the current literature. Station trends in annual total and extreme rainfall for 1961-2011 are spatially heterogeneous and largely not statistically significant. This differs with the results of earlier studies that show spatially coherent trends that tended to reverse in the vicinity of the South Pacific Convergence Zone (SPCZ). We infer that the difference is due to the Interdecadal Pacific Oscillation switching to a negative phase from about 1999, largely reversing earlier rainfall changes. Trend analyses for 1981-2011 show wetter conditions in the West Pacific Monsoon (WPM) region and southwest of the mean SPCZ position. In the tropical North Pacific it has become wetter west of 160 • E with the Intertropical Convergence Zone/WPM expanding northwards west of 140 • E. Northeast of the SPCZ and in the central tropical Pacific east of about 160 • E it has become drier. Our findings for the South Pacific subtropics are consistent with broader trends seen in parts of southern and eastern Australia towards reduced rainfall. The relationship between total and extreme rainfall and Pacific basin sea surface temperatures (SSTs) has been investigated with a focus on the influence of the El Niño-Southern Oscillation (ENSO). We substantiate a strong relationship between ENSO and total rainfall and establish similar relationships for the threshold extreme indices. The percentile-based and absolute extreme indices are influenced by ENSO to a lesser extent and in some cases the influence is marginal. Undoubtedly, larger-scale SST variability is not the only influence on these indices.
C limate data, and their associated metadata, provide the fundamental building blocks for climate research and the development of climate products, applications, and services. In the past decade or so, the requirements of climate researchers to analyze and detect climate change and develop seasonal-tointerannual prediction systems have increased the importance of climate data. Climate data are also required for the preparation of climate models, which are widely used for verification of seasonal-to-inter
[1] The large-scale nature of El Niño-Southern Oscillation (ENSO) impacts on rainfall in the western Pacific region is generally well known but in some regions, where there are relatively few observations and the terrain is mountainous, the details of the impacts are less obvious. Here we analyze rainfall data for the New Guinea region comprising station observations, reanalysis products, and satellite-based estimates in order to better understand some of these details. We find that most gridded products are limited due to their relatively coarse horizontal resolutions that fail to resolve topographic effects. However, the relatively fine resolution Tropical Rainfall Measurement Mission satellite-based product appears to provide reliable estimates and linear correlations between the data and the NINO34 sea surface temperature index provides an insight into the pattern of ENSO rainfall impacts. The first major finding is that the correlation patterns reveal that some highland regions are impacted differently to other surrounding regions, most likely because of the interaction between winds and topography. Second, we find that the association between ENSO and rainfall for stations in the New Ireland/New Britain region tends to be nonlinear, in the sense that warm (El Niño)/cool (La Niña) events cause a decrease in rainfall-the strong 2010-2011 La Niña event being a clear example. Both findings help explain why previous studies have tended not to identify a simple large-scale response of New Guinea rainfall to ENSO.
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