Do you have any indications of why the predictions differ so much? I'm only passingly familiar with the two datasets, but as an example you noted a north-south trend, but I'd note there's also a roughly similar elevation trend. Precipitation correlates with elevation, and understanding this relationship is a piece of what PRISM does. It also uses elevation to predict/interpolate precipitation. ERA5 doesn't explicitly do that, afaik, and models precipitation based on satellite observations + weather stations? It's a little unclear to me exactly how it works, but it seems like looking at covariates or understanding if there's a geospatial trend in the data (e.g., due to elevation or another factor) which isn't explicitly captured in a model might cause it to underpredict, or, conversely, cause another model to overpredict if it's overfit to that same trend.
Thanks for commenting Alex! I think ERA-5 has been shown to correlate poorly with gauge measurements in general (https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.4351) but not sure if this extends to ERA5-Land. I would assume a big difference is that there is no underlying assimilation/physical model for PRISM.
Do you have any indications of why the predictions differ so much? I'm only passingly familiar with the two datasets, but as an example you noted a north-south trend, but I'd note there's also a roughly similar elevation trend. Precipitation correlates with elevation, and understanding this relationship is a piece of what PRISM does. It also uses elevation to predict/interpolate precipitation. ERA5 doesn't explicitly do that, afaik, and models precipitation based on satellite observations + weather stations? It's a little unclear to me exactly how it works, but it seems like looking at covariates or understanding if there's a geospatial trend in the data (e.g., due to elevation or another factor) which isn't explicitly captured in a model might cause it to underpredict, or, conversely, cause another model to overpredict if it's overfit to that same trend.
Thanks for commenting Alex! I think ERA-5 has been shown to correlate poorly with gauge measurements in general (https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.4351) but not sure if this extends to ERA5-Land. I would assume a big difference is that there is no underlying assimilation/physical model for PRISM.