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

Abstract

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.

Changes in South Pacific rainfall bands in a warming climate

“…S1) and delivers considerable amounts of rainfall to South Pacific islands during austral summer 1,5,6 (December-February: DJF), which we focus on in the analyses presented here. The seasonal march of this ∼8,000-10,000-km-long rainband is largely controlled by the seasonal cycle of the underlying sea surface temperature (SST) field, with air-sea interactions playing a key role 7 .…”

Resistance and Resilience of A Stream Salamander To Supraseasonal Drought

“…These increases are associated with increased atmospheric water vapour and are consistent with observed warming (Figure 2.4). However, rainfall statistics are dominated by interannual to decadal-scale variations, and trend estimates are spatially incoherent (e.g., Peterson et al, 2002;Griffiths et al, 2003;Herath and Ratnayake, 2004). Moreover, only a few regions have data series of sufficient quality and length to assess trends in extremes reliably.…”

A multiscale framework for the origin and variability of the South Pacific Convergence Zone

“…This extends eastward over the Pacific: zonally in the Northern Hemisphere to form the intertropical convergence zone The SPCZ (Vincent, 1994) supplies rainfall locally for the communities on the southwest Pacific islands. Precipitation on these islands has significant variability on many time-scales: the Madden-Julian Oscillation (MJO) on intraseasonal time-scales (Matthews and Li, 2005); the El Niño-Southern Oscillation (ENSO) on interannual time-scales and the Interdecadal Pacific Oscillation (IPO: Folland et al, 2002) and longer time-scales (Griffiths et al, 2003). The SPCZ environment itself provides the necessary conditions for, and is the main location of, tropical cyclogenesis in the South Pacific (Vincent et al, 2011).…”