I am calculating changes in precipitation using the Delta method, wherein the relative changes are calculated thus:
Delta change = (modelled Future climatology (2050s) - modelled historical climatology (1981-2010)) / modelled historical climatology (1981-2010))
This Delta (or anomaly) data is added to the actual observations to produce a final bias corrected future projection for Precipitation using: Future projection = Observed climatology (1981-2010) * (1 + Delta change).
My problem is that there are some very large numbers being produced in the dataset (presumably due to dry areas having unrealistically large relative differences calculated between future and present). How can I account for this? They mention it in this paper: https://www.nature.com/articles/s41597-019-0343-8 but I don't follow exactly what they did:
We note that in very dry areas (i.e. monthly historical precipitation close to zero) relative changes could produce unreasonably large relative precipitation increases (e.g. Sahara Desert). To avoid this, we made two adjustments: (1) we set a threshold of 0.1 mm month−1 both for current and future GCM values, which prevents indetermination in Eq. 2; and (2) we truncate the top 2% of anomaly values to the 98th percentile value in the empirical probability distribution for each anomaly gridded dataset