How to find correlation between time-series of different units? I have 3 time-series data.


NDVI(normalized difference vegetation index) mean
Precipitation
Temperature 
All of these have their own unit. 
Now I want to find similarity/correlation between NDVI and precipitation,
NDVI and temperature. Basically, my aim is to find "NDVI is more correlated with precipitation or temperature".
Should I normalize precipitation and temperature to NDVI values?
I recommend you to scale all three time series to unitless values, with zero mean and standard deviation of 1. After that, you can search for correlation among normalized time series. Python has StandardScaler function that could help with it.