The percentile based indices require a special calculation method for years that lie inside the base period. Then, bootstrapping must be applied where the base period is modified: The index year is taken from the base period and is replaced by another year. Then, the percentile as well as the index is calculated for the new 30 year base period. This is done 29 times so that each year from the base period will be accounted twice. In the end, the mean of 29 indices is taken.<br>

The temperature related percentile based indices (*tx90p, tx10p, tn90p, tn10p*) require a special percentile calculation method for years that lie inside the base period. For that years, bootstrapping must be applied where the base period is modified: The index year is taken from the base period and is replaced by another year. Then, the percentile as well as the index is calculated for the new 30 year base period. This is done 29 times so that each year from the base period will be accounted twice. In the end, the mean of 29 indices is taken.<br>