Evaluation of the environmental stress index (ESI) for the southern hemisphere

The environmental stress index (ESI), constructed from ambient temperature, relative humidity, and solar radiation, was further evaluated from databases collected in Israel and New Zealand. High correlations were found between ESI and WBGT (R2=0.959 and R2=0.973 for Israel and New Zealand, respectively). However, for the New Zealand database, residuals were not distributed symmetrically around the zero line, which might be due to the difference in the global radiation spectrum. The ultraviolet radiation measurements were significantly higher in New Zealand than in Israel. As a consequence, a correction factor might be needed for ESI to be used in the southern hemisphere.