Editing IPCC:AR6/WGI/Chapter-Atlas (section)

=== Atlas.10.2 Assessment and Synthesis of Observations, Trends and Attribution ===

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Significant positive trends in temperature ranging from 0.15°C per decade (over the period 1953–2010) to 0.18°C per decade (over the period 1961–2011) are noted in the tropical western Pacific, where the significant increasing and decreasing trends in warm and cool extremes, respectively, are also spatially homogeneous ( [[#Jones--2013|Jones et al., 2013]] ; [[#Whan--2014|Whan et al., 2014]] ; [[#Wang--2016|Wang et al., 2016]] ). Similarly, much of the Caribbean region showed statistically significant warming (at the 95% level) over the period 1901–2010 (P.D. [[#Jones--2016|Jones et al., 2016]] b). Observation records in the Caribbean region indicate a significant warming trend of 0.19°C per decade and 0.28°C per decade in daily maximum and minimum temperatures, respectively, with statistically significant increases (at the 5% level) in the number of warm days and warm nights during 1961–2010 ( [[#Taylor--2012|]] [[#Taylor--2012|M.A. Taylor et al., 2012]] ; [[#Stephenson--2014|Stephenson et al., 2014]] ; [[#Beharry--2015|Beharry et al., 2015]] ).

A weather station-based annual precipitation trend analysis over 1901–2010 in the Caribbean region indicated some locations with detectable decreasing trends ( [[#Knutson--2018|Knutson and Zeng, 2018]] ), which were attributable in part to anthropogenic forcing. These include southern Cuba, the northern Bahamas, and the Windward Islands, although significant trends were not found over the shorter periods of 1951–2010 and 1981–2010. In the Caribbean islands, a dataset of the Palmer Drought Severity Index (PDSI) from 1950 to 2016 showed a clear drying trend in the region ( [[#Herrera--2017|Herrera and Ault, 2017]] ). The 2013–2016 period showed the most severe drought during the period and was strongly related to anthropogenic warming, which would have increased the severity of the event by 17% and its spatial extent by 7% ( [[#Herrera--2018|Herrera et al., 2018]] ). However, a seasonal analysis of observations grouped into large sub-regions of the Caribbean revealed no significant long-term trends in rainfall over 1901–2012 but significant inter-decadal variability (P.D. [[#Jones--2016|Jones et al., 2016]] b). Declines in summer rainfall (–4.4% per decade) and maximum five-day rainfall (–32.6 mm per decade) over 1960–2005 were reported for Jamaica ( [[#CSGM--2012|CSGM, 2012]] ), and an insignificant decrease in summer precipitation was observed for Cuba for 1960–1995 ( [[#Naranjo-Diaz--1998|Naranjo-Diaz and Centella, 1998]] ). Three of four stations examined for Puerto Rico exhibited declining JJA rainfall over 1955–2009 with the trend statistically significant at the 95% level for Canóvana ( [[#Méndez-Lázaro--2014|Méndez-Lázaro et al., 2014]] ). In the Caribbean, positive regional trends in precipitation and trends in extremes during 1961–2010 were found to be not statistically significant (at the 5% level; [[#Stephenson--2014|Stephenson et al., 2014]] ; [[#Beharry--2015|Beharry et al., 2015]] ). Positive trends in JJA rainfall over Cuba and Jamaica are seen in CRU, whereas they are negative over Cuba for GPCC; over eastern Hispaniola they are positive in CRU and negative in CHIRPS ( [[#Cavazos--2020|Cavazos et al., 2020]] ).

In Hawaii, between 1920 and 2012, over 90% of the islands showed reduced rainfall and streamflow, an increase in the frequency of days with zero flow ( [[#Strauch--2015|Strauch et al., 2015]] ; [[#Frazier--2017|Frazier and Giambelluca, 2017]] ), and robust positive trends in drought frequency and severity ( [[#McGree--2016|McGree et al., 2016]] ). Over the western Pacific, interannual and decadal variabilities also drive long-term trends in rainfall. Recent analysis of station data showed spatial variations in the mostly decreasing but non-significant trends in annual and extreme rainfall over the western Pacific from 1961 to 2011 ( ''low confidence'' ) ( [[#McGree--2014|McGree et al., 2014]] ). Over the southern subtropical Pacific, decreases in annual, JJA, SON and extreme rainfall, and increasing drought frequency in the western region, has been observed since 1951 ( [[#Jovanovic--2013|Jovanovic et al., 2013]] ; [[#McGree--2016|McGree et al., 2016]] , 2019).

Over the western Indian Ocean significant warming trends have been reported for Mauritius (1.2°C during 1951–2016; [[#MESDDBM--2016|MESDDBM, 2016]] ), La Réunion (0.18°C per decade over 1968–2019; [[#Météo-France--2020|Météo-France, 2020]] ) and Maldives ( [[#MEE--2016|MEE, 2016]] ). Both Mauritius and La Réunion have experienced rainfall decreases of 8% during 1951–2016 and 1.2% per decade during 1961–2019 with generally weak, non-significant rainfall trends during 1967–2012.

Assessing observed climate change for Small Islands is often constrained by low station density ( [[#Ryu--2014|Ryu and Hayhoe, 2014]] ; P.D. [[#Jones--2016|Jones et al., 2016]] a), digitization requirements or data-sharing limitations (P.D. [[#Jones--2016|Jones et al., 2016]] a). Station data typically have longer temporal coverage relative to satellite products but are limited in spatial coverage ( [[#Cavazos--2020|Cavazos et al., 2020]] ). For Small Island nations, spatial gaps between observations can be very large due to the isolation of the islands ( [[#Wright--2016|Wright et al., 2016]] ). Additionally, over past decades, the number of station observations has declined substantially in Mauritius ( [[#Dhurmea--2019|Dhurmea et al., 2019]] ), Hawai’i ( [[#Bassiouni--2013|Bassiouni and Oki, 2013]] ; [[#Frazier--2017|Frazier and Giambelluca, 2017]] ) and most Pacific Island countries since the 1980s ( [[#Jones--2013|Jones et al., 2013]] ; [[#McGree--2014|McGree et al., 2014]] , 2016). In Fiji, meteorological stations were located on or by the coast and are sparse in the interior ( [[#Kumar--2013|Kumar et al., 2013]] ). Notable topography and land use may result in changes in climatic conditions over small distances ( [[#Foley--2018|Foley, 2018]] ), making the observational density particularly relevant.

Moreover, many stations have little metadata available, including those in Vanuatu, the Solomon Islands and Papua New Guinea ( [[#Whan--2014|Whan et al., 2014]] ). Compared to earlier decades, few metadata are currently being documented in the western Pacific islands ( [[#McGree--2014|McGree et al., 2014]] ), which will challenge the homogenization of long-term observational records. Challenges in the Caribbean include maintaining continuous daily time series with metadata, converting climatological data into digital formats and making them freely available ( [[#Stephenson--2014|Stephenson et al., 2014]] ; [[#Beharry--2015|Beharry et al., 2015]] ; P.D. [[#Jones--2016|Jones et al., 2016]] a). This is also an issue in the Pacific as many data are kept in national (local) databases, with only a fraction having been incorporated into global datasets ( [[#Whan--2014|Whan et al., 2014]] ).

Because of the small number of stations used for interpolation and the complex mountainous topography, gridded product for these small islands should be interpreted with caution ( [[#Frazier--2017|Frazier and Giambelluca, 2017]] ). For the Antilles, the error in estimating CRU2.0 monthly precipitation can stand locally between 20% and 40%. Over the Caribbean, [[#Cavazos--2020|Cavazos et al. (2020)]] found a discrepancy across gridded observational datasets (CRU, CHIRPS and GPCP) in detecting orographicprecipitation, especially during boreal summer, making their use in climate model evaluation challenging ( [[#Herrera--2017|Herrera and Ault, 2017]] ). Furthermore, some reanalysis products such as the 0.7° × 0.7° ERA-Interim reanalysis are not adequate as many of the smaller Caribbean islands are not represented as land (P.D. [[#Jones--2016|Jones et al., 2016]] a).

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