I have rainfall time series of 85 points from 1901-2013. I want to check whether the mean rainfall during 1901-1970 is significantly different than that of the mean rainfall during 1971-2013.
Here, the data would not 'necessarily' follow the normal distribution. So, one of the main assumption for applying t-test may not be fulfilled.
Now as the length of the dataset for two samples would be 70 and 43, can I use the paired t-test or Welch's t-test assuming that the length is sufficient to circumvent the assumption of normality.
What should be the minimum length of data to overcome the normality condition in t-test, is 43 good enough?
In case, it's not then what test should be applied?