The monthly data is now available for the time period January 1982 to January 2020.
For the GPCC Monitoring Product, quality-controlled station data from worldwide routine measurements (7000 to 9000 SYNOP and CLIMAT reports per month) are used to calculate the monthly precipitation over land areas. It is a routinely monthly gridded dataset that is updated on a continuous basis, available with a 1°x1° grid resolution.
https://icdc.cen.uni-hamburg.de/1/daten/atmosphere/gpcc.html
