Duke William’s 1066 Campaign, the Historical Climatology

The Palmer Drought Severity Index (PDSI) provided local precipitation proxies for March – August and June – August back to the time of the battle at the precipitation points in Figure 1 using the CCSM4 (Gent et al., 2011; Landrum et al., 2013) and MPI-ESM-P (Giorgetta et al., 2013) models. These values are represented as dimensionless anomalies in reference to the mean in mm for 1928 - 2003 (Ljungqvist et al., 2019). The PDSI also provided measured precipitation values in mm and temperature values in degrees Celsius per month for the 1928 – 2003 reference period at the same points (Ljungqvist et al., 2019). The Paris-London Westerly Index which estimates the North Atlantic Oscillation on a monthly scale from 1692 to 2007 was accessed to estimate weather patterns. The data was calculated by Cornes et al. (2013). Monthly air pressure data from 1659 to 1999 was provided for 50^oN 0^oE in a reconstruction by Luterbacher et al. (2002).