I am working with a multivariate time series (with daily data) of approximately 40 years.
It consists of the data of two stations (dataset A & dataset B) measuring both the river level and the streamflow of two neighbouring (but not connected) rivers. The datasets are correlated (specificly the streamflow), however the variance of both time series is pretty different.
Additionally I have the data of two closeby percipitation stations.
Dataset B ends 6 years before dataset A ends. I am looking for a way to impute the 6 years of missing data of station B at the end of the time series using the data of station A and the percipitation stations.
Many papers have been published about the imputation of missing values at random, however I have not found a good method for imputation of a single, long period of missing data. I have tried multiple methods in R (mtsdi, mice, iVAR), all without satisfactory results.
1) What is the best method to impute a single, long period of missing data?
2) What is the best way to test the functionality of the used method? Up until now i picked a period directly before the data gap, deleted the last 6 years, imputed these 6 years and compared them to the original time series. I am wondering if this process can be automated not only for the 6 years before the data gap but also for other 6 year periods within the dataset.