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

==== Atlas.1.3.3 Spatial Scales and Reference Regions ====

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Many factors influence the spatial scales and regions over which climate information is required and can be reliably generated. Despite all efforts in researching, analysing and understanding climate and climate change, a key factor in determining spatial scales at which analysis can be undertaken is the availability and reliability of data, both observational and from model simulations. In addition, information is required over a wide range of spatial domains defined either from a climatological or geographical perspective (e.g., a region affected by monsoon rainfall or a river basin) or from a socio-economic or political perspective (e.g., least-developed countries or nation states). [[IPCC:Wg1:Chapter:Chapter-1|Chapter 1]] provides an overview of these topics ( [[IPCC:Wg1:Chapter:Chapter-1#1.5.2|Section 1.5.2]] ). This subsection discusses some relevant issues, summarizes recent advances in defining domains and spatial scales used by AR6 analyses and how these can be explored with the Interactive Atlas.

Recent IPCC reports – AR5 Chapter 14 ( [[#Christensen--2013|Christensen et al., 2013]] ) and SR1.5 [[IPCC:Wg1:Chapter:Chapter-3|Chapter 3]] ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ) – have summarized information on projected future climate changes over sub-continental regions defined in the SREX report ( [[#Seneviratne--2012|Seneviratne et al., 2012]] ) and later extended in AR5 from the 26 regions in SREX to include the polar, Caribbean, two Indian Ocean, and three Pacific Ocean regions (hereafter known as AR5 WGI reference regions; Figure Atlas.2a). In recent literature, new sub-regions have been used, for example for North and South America, Africa and Central America, together with the new definition of reference oceanic regions. [[#Iturbide--2020|Iturbide et al. (2020)]] describes an updated version of the reference regions which is used in this report (hereafter known as AR6 WGI reference regions) and is shown in Figure Atlas.2b. The goal of these subsequent revisions was to ensure that they represented sub-continental areas of greater climatic coherency.

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[[File:f3463ff5a39b129b57a3c398f277892f IPCC_AR6_WGI_Atlas_Figure_2.png]]

'''Figure Atlas.2''' '''|''' '''WGI reference regions used in the (a) AR5 and (b) AR6 reports''' ( [[#Iturbide--2020|Iturbide et al., 2020]] ). Asterisks indicate regions that extend across both sides of the map. The latter includes both land and ocean regions and it is used as the standard for the regional analysis of atmospheric variables in the Atlas chapter and the Interactive Atlas. The codes used in the Interactive Atlas are included in the figure. The full description of the regions (grouped by continents) is as follows. North America: NWN (North-Western North America), NEN (North-Eastern North America), WNA (Western North America), CNA (Central North America), ENA (Eastern North America); Central America: NCA (Northern Central America), SCA (Southern Central America), CAR (Caribbean); South America: NWS (North-Western South America), NSA (Northern South America), NES (North-Eastern South America), SAM (South American Monsoon), SWS (South-Western South America), SES (South-Eastern South America), SSA (Southern South America); Europe: GIC (Greenland/Iceland), NEU (Northern Europe), WCE (Western and Central Europe), EEU (Eastern Europe), MED (Mediterranean); Africa: MED (Mediterranean), SAH (Sahara), WAF (Western Africa), CAF (Central Africa), NEAF (North Eastern Africa), SEAF (South Eastern Africa), WSAF (West Southern Africa), ESAF (East Southern Africa), MDG (Madagascar); Asia: RAR (Russian Arctic), WSB (West Siberia), ESB (East Siberia), RFE (Russian Far East), WCA (West Central Asia), ECA (East Central Asia), TIB (Tibetan Plateau), EAS (East Asia), ARP (Arabian Peninsula), SAS (South Asia), SEA (South East Asia); Australasia: NAU (Northern Australia), CAU (Central Australia), EAU (Eastern Australia), SAU (Southern Australia), NZ (New Zealand); Antarctica: WAN (Western Antarctica), EAS (Eastern Antarctica). The definition of the regions and companion notebooks and scripts are available at the Atlas repository ( [[#Iturbide--2021|Iturbide et al., 2021]] ). Figure from [[#Iturbide--2020|Iturbide et al. (2020)]] .

The rationale followed for the definition of the reference regions was guided by two basic principles: 1) climatic consistency and better representation of regional climate features, and 2) representativeness of model results (i.e., sufficient number of model grid boxes). The finer resolution of CMIP6 models (as compared, on average, to CMIP5) yields better model representation of the reference regions allowing them to be revised for better climatic consistency (e.g., dividing heterogeneous regions) while preserving the model representation. Figure Atlas.3 illustrates this issue, displaying the number of grid boxes (over land for land regions) in the AR6 reference regions for two Interactive Atlas reference grids of horizontal resolutions of 1° and 2°, representative of the typical resolution of CMIP6 and CMIP5 models respectively. This figure shows that the new reference regions are well suited for the assessment of model results, with poorest model coverage for the New Zealand (NZ), Caribbean (CAR) and Madagascar (MAD) regions.

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[[File:4ff1c658b5d44e45a83818da9a5ea2e1 IPCC_AR6_WGI_Atlas_Figure_3.png]]

'''Figure Atlas.3''' '''|''' '''Number of land grid boxes for each AR6 WGI reference region for the reference grids representative of (a) CMIP6 and (b) CMIP5, at 1° and 2° resolution respectively.''' Colour shading indicates regions with fewer than 250 grid boxes (the darkest shading is for regions with fewer than 20 grid boxes). The polygons show the AR6 WGI reference regions of Figure Atlas.2. Detailed information on the grids used is provided at the Atlas repository ( [[#Iturbide--2021|Iturbide et al., 2021]] ).

The AR6 WGI (land and open ocean) reference regions are used in the Interactive Atlas as the default regionalization for atmospheric variables. However, these regions are not optimum for the analysis of oceanic variables since, for instance, the five upwelling regions (Canary, California, Peru, Benguela and Somali) are mostly included in ‘land’ regions. Therefore, the alternative set of oceanic regions defined by their biological activity (Figure Atlas.4) is used in the Interactive Atlas for the regional analysis of oceanic variables (see [[#Fay--2014|Fay and McKinley, 2014]] ; [[#Gregor--2019|Gregor et al., 2019]] ). Due to the many potential definitions of the regions relevant for WGI and WGII, some additional typological and socio-economic regions have also been included in the Interactive Atlas.

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[[File:0ac0c25e16d8520c0959e0aac9b6f406 IPCC_AR6_WGI_Atlas_Figure_4.png]]

'''Figure Atlas.4''' '''|''' '''Typological and socio-economic regions used in the Interactive Atlas. (a)''' Eleven ocean regions defined by their biological activity and used for the regional analysis of oceanic variables; '''(b)''' ocean regions for Small Islands, including the Caribbean (CAR) and the north Indian Ocean (ARS and BOB); '''(c)''' land monsoon regions of North America, South America, Africa, Asia and Australasia; '''(d)''' major river basins; '''(e)''' mountain regions; '''(f)''' WGII continental regions. These regions can be used alternatively to the reference regions for the regional analysis of climatic variables in the Interactive Atlas. The definition of the regions and companion notebooks and scripts are available at the Atlas repository ( [[#Iturbide--2021|Iturbide et al., 2021]] ).

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