ISIMIP2a/3a: very large daily precipitation values found in GSWP3 climate input data

Posted by Matthias Büchner on Dec. 15, 2020

In the GSWP3 climate data provided for driving ISIMIP2a and 3a simulations, we found daily precipitation amounts exceeding 1000 mm/day in single grid cells and time steps. Those large values have been detected by applying our new QC-Tool to ISIMIP3a HydroPy runoff output data. The tool identified particularly large runoff values. We then traced those back to the associated precipitation inputs.

We found a maximum daily precipitation value of 0.016 kg m-2 s-1 in our GSWP3 data. This is equivalent to 1.3 meters of rain falling on that day, which is much larger than the valid maximum value for daily total runoff (0.004 kg m-2 s-1 or 345 mm/day) defined by the global water sector. We found that the number of exceedances of this valid maximum value decreases over time from about 600 occurrences per early decade to about 200 occurrences per late decade. Exceedances mainly occur in high precipitation areas (Monsoon regions, Amazon basin).

The GSWP3 data we provide for ISIMIP2a and 3a simulation was provided to us by Hyungjun Kim in 2014. Meanwhile, the data set has seen many updates, one of which addresses biases in early-20th-century precipitation. It is currently unclear how we will proceed with this issue. We will decide after evaluating a more recent version of GSWP3 and will share our decision soon.

GSWP3 Precipitation