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

==== [[#Atlas.5.5.2|Atlas.5.5.2]] Assessment and Synthesis of Observations, Trends and Attribution ====

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Since AR5, there has been an increasing number of studies on past climate change in South West Asia though meteorological stations are sparsely scattered in the region. They are mainly located in the plains below 2 km of altitude, very scarce in mountainous areas and have declined in number in WCA since the end of the Soviet Union in 1991. This increases the uncertainty in both temperature and precipitation trends, particularly for elevated areas ( ''high confidence'' ) ( [[#Christensen--2013|Christensen et al., 2013]] ; [[#Huang--2014|Huang et al., 2014]] ). So researchers use other sources of climate data in the region, particularly freely available gridded data (Annex I).

Globally, drylands showed an enhanced warming over the past century of 1.2°C–1.3°C, significantly higher than the warming over humid lands (0.8°C–1.0°C) (J. [[#Huang--2017|]] [[#Huang--2017|Huang et al., 2017]] ). A strong increase in annual surface air temperature of 0.27°C–0.47°C per decade has been found over WCA between 1960 and 2013 ( ''very high confidence'' ) ( [[#Han--2013|Han and Yang, 2013]] ; [[#Li--2013|Li et al., 2013]] ; [[#Hu--2014|Hu et al., 2014]] , 2017; [[#Huang--2014|Huang et al., 2014]] ; [[#Deng--2017|Deng and Chen, 2017]] ; [[#Zhang--2017|Zhang et al., 2017]] , 2019a; H. [[#Guo--2018|]] [[#Guo--2018|Guo et al., 2018]] ; [[#Haag--2019|Haag et al., 2019]] ; [[#Yu--2019|Yu et al., 2019]] ) ''.'' Warming is most prominent in the spring based on the CRU dataset with rates ''likely'' ranging from 0.64°C–0.82°C per decade ( [[#Hu--2014|Hu et al., 2014]] ). Analysis of seasonal temperature trends based on high-resolution 1 km × 1 km downscaled dataset CHELSA and 20 stations in Uzbekistan has confirmed the maximum significant trend in temperature from 0.6°C up to 1°C per decade in spring from 1979 to 2013 and no significant trend in winter ( [[#Khaydarov--2019|Khaydarov and Gerlitz, 2019]] ). There is ''very high confidence'' ( ''robust evidence'' , ''high agreement'' ) that the shrinking of the Aral Sea has induced an increase in surface air temperature around the Aral Sea region in the range of 2°C–6°C ( [[#Baidya%20Roy--2014|Baidya Roy et al., 2014]] ; [[#McDermid--2017|McDermid and Winter, 2017]] ; [[#Sharma--2018|Sharma et al., 2018]] ). The plateau of Iran has experienced significant increases in the average monthly values of daily maximum and minimum temperatures with spatially varying rates of 0.1°C–0.3°C up to 0.3°C–0.4°C per decade and greater spatial variation in minimum temperatures ( ''high confidence'' ) ( [[#Mahmoudi--2019|Mahmoudi et al., 2019]] ; [[#Fathian--2020|Fathian et al., 2020]] ; [[#Sharafi--2020|Sharafi and Mir Karim, 2020]] ).

Observed warming over northern ARP is higher than over the south, where minimum temperatures are increasing faster than maximum temperatures ( [[#Almazroui--2020a|Almazroui, 2020a]] ). The rate of mean temperature increase is estimated at 0.10°C per decade over 1901–2010 ( [[#Attada--2019|Attada et al., 2019]] ), while it has reached 0.63°C ( ''likely'' in the range of 0.24°C–0.81°C) per decade for the more recent period of 1978–2019 ( [[#Almazroui--2020a|Almazroui, 2020a]] ).

An overall increasing trend of annual precipitation (0.66 mm per decade) was found over Central Asia based on GPCC v7 data for the period 1901–2013 ( [[#Hu--2017|Hu et al., 2017]] ), but annual trends were found not significant over the shorter period 1960–2013 (Figure Atlas.11 and Interactive Atlas). Winter precipitation saw a significant increase of 1.1 mm per decade ( [[#Song--2016|Song and Bai, 2016]] ). These estimates have ''low'' to ''medium confidence'' since the satellite precipitation products have large systematic and random errors in mountainous regions. Moreover CMORPH and TRMM products fail to capture the precipitation events in the ice/snow covered regions in winter and show a substantial false-alarm percentage in summer, but the gauge-corrected GSMAP performs better than other products ( [[#Song--2016|Song and Bai, 2016]] ; [[#Guo--2017b|Guo et al., 2017b]] ; [[#Hu--2017|Hu et al., 2017]] ; S. [[#Chen--2019|]] [[#Chen--2019|Chen et al., 2019]] ). Over the elevated part of eastern WCA precipitation increases in the range of 1.3–4.8 mm per decade during 1960–2013 were observed ( ''very high confidence'' ) ( [[#Han--2013|Han and Yang, 2013]] ; [[#Li--2013|Li et al., 2013]] ; [[#Hu--2014|Hu et al., 2014]] , 2017; [[#Huang--2014|Huang et al., 2014]] ; [[#Deng--2017|Deng and Chen, 2017]] ; [[#Zhang--2017|Zhang et al., 2017]] , 2019a; H. [[#Guo--2018|]] [[#Guo--2018|Guo et al., 2018]] ; [[#Haag--2019|Haag et al., 2019]] ; [[#Yu--2019|Yu et al., 2019]] ). Reductions in spring precipitation and increases in winter have been reported for Uzbekistan over the period 1979–2013 based on station data but these are not significant ( [[#Khaydarov--2019|Khaydarov and Gerlitz, 2019]] ). There is ''very low confidence'' of the impact of the Aral Sea shrinking on precipitation ( [[#Chen--2011|Chen et al., 2011]] ; [[#Jin--2017|Jin et al., 2017]] ).

A decreasing trend of precipitation is reported for ARP with the mean value of –6.3 mm per decade (range of –30 mm–16 mm) for the period 1978–2019 ( ''low confidence'' ) with large interannual variability over Saudi Arabia, which covers 80% of the region ( [[#AlSarmi--2011|AlSarmi and Washington, 2011]] ; [[#Almazroui--2012|Almazroui et al., 2012]] ; [[#Donat--2014|Donat et al., 2014]] ). The same decreasing trend in precipitation totals and an increasing trend in the number of consecutive dry days are found for most of the Iranian Plateau ( ''medium confidence'' ) ( [[#Rahimi--2019|Rahimi and Fatemi, 2019]] ; [[#Fathian--2020|Fathian et al., 2020]] ; [[#Sharafi--2020|Sharafi and Mir Karim, 2020]] ). January-to-March mean snow cover and depth over mountainous areas decreased between 2000 and 2019 ( ''low'' to ''medium confidence'' due to ''limited evidence'' ) ( [[#Safarianzengir--2020|Safarianzengir et al., 2020]] ).

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