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 Y.Y. Deng et al. / Global Environmental Change 31 (2015) 239–252

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Table 1 Data sets used for the GIS modelling of land- and sea-based resources. Data

Resolution

Source

Reference

Land

Elevation Land cover/use Population Country borders Railways Solar irradiance Wind speed (land)*

1 km 1 km 5 km $2 km 10 km 40 km 19 km

USGS (-EROS) GTOPO30 USGS GLCC v2 NASA–SEDAC v3 VMAP0 NGA/USGS VMAP0/VMAP1 NASA CRU, CL2.0

USGS (1996) Loveland et al. (2000) CIESIN et al. (2005) NIMA (2000) NIMA (2000) LaRC ASDC (2012) New et al. (2002)

Land/sea

Wind speed (all)* Protected areas

120 km 1 km

CISL WDPA

CISL (2012) IUCN and UNEP (2011)

Sea

Coastlines Ocean depth Maritime use Reefs & marshes Offshore borders

$2 km 2 km 1 km 1 km $2 km

VMAP0 NOAA NCEAS impacts NCEAS ecosystems Exclusive Economic Zones

NIMA (2000) Amante and Eakins (2009) Halpern et al. (2008) Halpern et al. (2008) VLIZ (2012)

Category

The wind speed on land was determined as an average between these two datasets as the CRU dataset had a better resolution but suffered from sparse data in some world regions (China, Africa, South America).

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� Wind: Non-protected forests were not excluded for wind power production (but received a lower availability in the ﬁnal step). Land cover – Ice, Water, Coast, Cliffs, Dune, Rock: Areas of these land cover types were excluded for all technologies. Protected areas: � From the World Database on Protected Areas (WDPA) data set (see Table 1) all classiﬁed protected areas were excluded (Natura 2000 and Cat. I–VI). Non-classiﬁed areas were not included in this study due to insufﬁcient information. � All land cover classes of ‘rain forest’ and ‘tropical forest’ have been fully excluded. Slope: � Solar – PV and Wind: Grid cells (1 km Â 1 km) with an average slope of more than 158 ($27%) were excluded. � Solar – CSP: Grid cells (1 km Â 1 km) with an average slope of more than 28 ($4%) were excluded. Resource intensity: � Solar – CSP: Areas with a direct normal irradiance value of less than 1900 kWh/m2/a were excluded for CSP. Availability of nearby water was not used as an exclusion criterion as technological developments are currently underway to minimise reliance on water for CSP. � Solar – PV: No areas were excluded based on resource intensity for PV as current practice shows that latitude is not a strong factor in determining where PV is installed and there is still signiﬁcant price reduction potential in PV which would likely render all areas within reach of cost-effectiveness. However, we note that the lowest horizontal irradiation levels found at the latitudes included in this study are around 800 kWh/m2/a. � Wind: To reﬂect the fact that areas of low wind speed are unlikely to see signiﬁcant investment in wind power installations we excluded areas with low average wind speeds in our calculations. The economically feasible minimum average wind speed is heavily dependent on local factors. For this global study, we implemented a critical cut-off of 6 m/s at hub height, with an assumption of average hub-height rising from 80 m now to 90 m for 2030 and 2070 (see also Supplementary Information online). Only areas with average wind speeds below this cut-off in four out of four quarters within a year were excluded.

2.1.2. Sea-based wind resource The area available for sea-based wind power installations is restricted by the following factors which have been used to

estimate suitable offshore area based on the data sources listed in Table 1: � Economic zone attribution: Only offshore areas attributed to a country jurisdiction have been included in this study. In case of joint jurisdiction the area has been split evenly between the administrating countries. Disputed areas have been completely excluded from the analysis. � Sea ice: Areas likely to be impacted by sea ice have been excluded by following the winter sea ice line around the Arctic and by implementing a general cut-off at 608 latitude in the Antarctic. � Ocean ﬂoor depth: Current technology for offshore wind power primarily relies on pylons driven into the sea-bed. This technology is already in use up to 50 m ocean depth. At (much) higher depths it is expected that ﬂoating turbine technology will be deployed. This technology is expected to be deployed within the study time horizon (up to 2070). There is no established upper limit for the depths this technology can reach; we have used a cautious cut-off of 1000 m depths; i.e. offshore areas with deeper ocean ﬂoor depths have been excluded. � The distance from shore is not a technical limitation per se, but areas very far from the coast have been assumed to be too costly to connect to land for the foreseeable future. We have used a critical cut-off of 200 km. It is noted, however, that most areas further than 200 km offshore would have been excluded in the previous steps on ocean ﬂoor depth and exclusive economic zones anyway. � Protected zones: Where data on ecosystems and protected zones was available, these have been excluded, but freely available data is sparse. Most of the areas excluded in this step were identiﬁed through the WDPA data set with some additional exclusions of salty marshes and rocky reefs from NCEAS (see Table 1). � Maritime use: Data on maritime use is not comprehensive. We have excluded the shipping lanes, areas of artisanal ﬁshing and oil rigs (including buffer zones) contained in a dataset provided by NCEAS (see Table 1) to estimate areas unavailable for offshore wind parks due to prior uses. This will lead to underestimates in some areas (only 10% of heavy shipping trafﬁc is logged in the NCEAS data set) and overestimates in other areas (all existing oil rigs are excluded but it is likely that several of them will have been dismantled by 2030/2070). � Resource intensity – wind speed: In analogy with the approach for onshore wind above, we implemented a critical cut-off of 8 m/s at hub height, with an assumption of average hub-height