Hi I am creating an isoscape model in which I am plotting 2H and 18O of precipitation. Until now I have always used ordinary kriging for the interpolation, but I am somewhat dissatisfied with the results. Since the data I use for interpolation comes from the precipitation, I assume that the expected value cannot be constant. However, this is assumed with ordinary kriging. Since universal kriging adds a trend to the data, this seems more sensible to me in this case. Therefore, I would like to ask which of these two kriging models is suitable for my interpolation and which trend would you recommend (in case of Universal Kriging) for the interpolation of precipitation data?