Aggregating runoff data in a hydrological catchment
I have a question regarding the runoff data from the GLDAS dataset and the way
I should aggregate it within a hydrologic catchment.
I have downloaded the mean monthly runoff data (Qs_acc & Qsb_acc variables from GLDAS Noah Land Surface Model L4 monthly 0.25 x 0.25 degree V2.0) and one of the downloaded netCDF files is attached for your consideration. I want to aggregate the total runoff data in a catchment and compare it with observed runoff values from a hydrologic station located in the downstream of the catchment. Therefore, I have first got spatial subsets of storm runoff (Qs_acc) and baseflow (Qsb_acc) grids within the catchment and then summed them up to get the total runoff values. Then I calculated monthly average values for the whole area (by averaging total runoff from all existing grids in the catchment for each month). This way, I guess that I'll get a time series of monthly runoff estimations in 'kg m-2' which is equal to 'mm'.
However, I get very low runoff values (between 0-1 mm/month). The Vmax values in the attribute table of the netCDF files for Qs_acc and Qsb_acc are given as 5.6851 and 3.7703, respectively while the corresponding observed runoff values are around 10-50 mm/month. Do you have any idea about the possible underestimation of runoff values in GLDAS dataset or maybe my calculation is wrong?
Any tips or advice in this regard is much appreciated.