## 3 Results  
### Hydroclimate and Wind Regimes at the Focus Sites  
Wind speeds at a height of 100 m AGL from the ERA5 reanalysis [124] at the six focus study locations (Table 1) are summarized in Figure 4c. Consistent with observational WS data, all six locations exhibit probability distributions that are consistent with substantial wind resources. The fidelity of ERA5 wind speeds varies in space and there is lowest fidelity in regions of complex terrain [136]. This is also evident in comparisons of the Weibull parameters in ERA5 relative to the measurements from coastal Canada (WEICan) and the US SGP. At the US SGP location, the measurements at 90 m AGL indicate a Weibull \(A\) and \(k\) of 8.96 ms\({}^{-1}\) and 2.183, while the ERA5 output for 100 m AGL indicates values of 7.55 ms\({}^{-1}\) and 2.391, which suggests a negative bias in the wind speeds at this location and a narrowing of the probability distribution. The negative bias at the US SGP site is consistent with past research that has indicated negative bias in ERA5 wind speeds over western North America [136]. At WEICan (coastal Canada), the Weibull \(A\) and \(k\) derived from observations at 80 m are; 10.3 ms\({}^{-1}\) and 2.001, respectively, while those from ERA5 for 100 m AGL are 10.7 ms\({}^{-1}\) and 2.239, also indicating a substantially narrower probability distribution from ERA5. For this reason, the joint probability distributions presented herein use only local wind speed observations. It should be noted that much closer agreement is found for the onshore site in Denmark consistent with the surrounding flat terrain. ERA5 wind speeds at 100 m AGL have a Weibull \(A\) of 8.40 ms\({}^{-1}\) and \(k\) = 2.368 while similar values computed from the observations from the cup anemometer at 94 m AGL are; 8.0 ms\({}^{-1}\) and 2.4. As expected based on the site descriptions in Section 2.3, coastal Norway exhibits the highest frequency of precipitation and is the location with highest annual mean precipitation (2250 mm). The US SGP exhibits a high frequency of hail and the highest values for the 90 th, 95 th and 99 th percentile RR (Table 2). Based on the four years of data from the Parsivel\({}^{2}\) disdrometer non-zero precipitation is reported during about 4.2% of all 1 min records and the 90 th, 95 th and 99 th percentile 1 min RR are; 4.18, 7.72 and 31.3 mmhr\({}^{-1}\), respectively. Thus, 1% of minutes when precipitation is falling (or 220 min in an average year) exhibit a RR > 31.3 mmhr\({}^{-1}\). Precipitation is more frequently observed at coastal Canada, coastal UK, coastal Norway, North Sea, and Denmark, but each of those sites has a much lower frequency of hail reports. Further all have considerably lower 99 th percentile RR of 9-10 mmhr\({}^{-1}\) (coastal Canada, coastal Norway, and coastal UK) and \(\approx\)7-8 mmhr\({}^{-1}\) (North Sea and Denmark) (Table 2). These analyses illustrate that the US SGP exhibits a hydroclimate that differs substantially relative to sites in Europe with respect to parameters of importance to wind turbine blade LEE. Indeed, hail may dominate LEE in the US SGP [92], in contrast to northern Europe where the hydroclimate is dominated by liquid precipitation, hail is very infrequent (Table 2) and thus kinetic energy transfer to the blades is likely dominated by rain [137; 138]. This would seem to imply that exclusion of consideration of hail in whirling-arm experiments may lead to inaccurate assessments of blade coating lifetimes for wind turbines deployed in regions such as the US SGP and in other regions with high hail frequency such as southern Europe, Asia, Africa and Australia (Figure 2).