## 2 Materials and Methods
### Detailed Information on Gridded Precipitation Products (GPPs)
The European Atmospheric Reanalysis (ERA-5), the 5 th generation global atmospheric reanalysis product with an upgraded atmospheric model and assimilation system, provides data from 1950-1978 (preliminary version) and from 1979 up to now at the spatial resolution of 0.25\({}^{\circ}\). The European Centre released the product for Medium-Range Weather Forecasts (ECMWF) [36; 37]. ERA-5 provides hourly data on several land-surface, atmospheric, and sea-state variables, along with uncertainty estimates [38; 39]. It produces atmospheric variables at 139 pressure levels using a more advanced 4D-var integration scheme and is available at hourly steps [40]. As the ERA-Interim reanalysis is substituted by ERA-5 dated 31 August 2019, it is important to evaluate whether ERA-5 can increase performance compared to ERA-Interim before it can be used in any application. ERA-5 data is available at the ECMWF portal [[https://cds.climate.copernicus.eu/#](https://cds.climate.copernicus.eu/#)]([https://cds.climate.copernicus.eu/#](https://cds.climate.copernicus.eu/#))!/search?text=ERA5&type=dataset (accessed on 19 October 2020). More detailed information is written in [36]. Here, we accessed the total precipitation data on single levels (1981-2009) at hourly timestep and summed it up to a daily timescale. Nevertheless, ERA-5 provides total precipitation in equivalent meter units; hence the unit conversion from meter to millimeter is substantial compared to gauge observation. APHRODITE stands for the Asian Precipitation-high Resolved Observational Data Integration Towards Evaluation of Water Resources. It is advanced with a high-resolution daily precipitation product that was elaborated by the collaboration of the Research Institute for Humanity and Nature (RIHN) Japan and the Meteorological Research Institute of Japan Meteorological Agency (JMA/MRI) derived from a dense rain gauges observational network in Asia. It has been used by serval researchers, specifically in the UIB region [26; 41; 42]. More detail about the algorithm can be found in [43]. However, the high-resolution (0.05\({}^{\circ}\)) precipitation product is prohibited for public use and is available only for partner institutes. Henceforth, we accessed the latest improved daily dataset for Monsoon Asia (APHRO_MA_V1101 and APHRO_MA_V1101 EX_R1), covering 60.0E-150.0E, 15.0S-55.0N at a high spatial extent of 0.25\({}^{\circ}\) for the periods extending from 1981-2007 and 2007-2009 respectively. It is accessible from [[http://www.chikyu.ac.jp/precip/](http://www.chikyu.ac.jp/precip/)]([http://www.chikyu.ac.jp/precip/](http://www.chikyu.ac.jp/precip/)) (accessed on 8 September 2020). Princeton Global Meteorological Forcing Dataset (PGMFD) for land surface modeling is a blend of gauge and reanalysis data developed by Princeton University. The PGMFD product provides various climatic variables, including precipitation at the spatial resolutions of 1.0\({}^{\circ}\), 0.5\({}^{\circ}\), and 0.25\({}^{\circ}\) and temporal resolutions of 3 h, daily and monthly, from 1948 to 2010 for a global scale. This dataset is created by combining reanalysis from the National Centers for Environmental Prediction-National Center for Atmospheric Research(NCEP-NCAR), also denoted as (NCEP reanalysis) and a group of globally gauged-based products. To generate the final PGMFD precipitation dataset, four products such as TRMM 3-h real-time data, NCEP reanalysis, Climatic Research Unit (CRU) monthly precipitation data, and GPCP daily precipitation data, are used in various processing mechanisms [44]. The PGMFD data has high spatial resolutions and global coverage that shows this product has multiple potential applications and has been used only in the UIB region [45], where JRB was excluded; therefore, we selected this product in our study to evaluate its credibility.