A modified hydrologic model for examining the capability of global gridded PET products in improving hydrological simulation accuracy of surface runoff, streamflow and baseflow

•SWAT model was modified to examine the capability of PET products in improving hydrological simulation accuracy.•Distributed input and higher spatial resolution of PET products are more conducive to hydrological modeling.•The input of PET products has a great impact on streamflow and baseflow, followed by surface runoff.•The accuracy of PET products should be improved from both improving PET products and considering water budget closure. Terrestrial evapotranspiration (ET), which links water and energy exchanges between atmosphere, land surface and underground water, significantly affects hydrological modelling. However, accurate ET estimation is still a great challenge for hydrological models. Currently, most hydrological models obtain ET mainly from their built-in potential evapotranspiration (PET) modules due to lack of observations. Note that the ET obtained in this way cannot be verified by observations and inevitably brings large model uncertainty. Fortunately, several PET products have been produced based on satellite remote sensing and/or reanalysis climate model output with global coverage and high spatiotemporal resolution, providing a great opportunity for tunning hydrological models. However, the accuracy of global gridded PET products varies in different regions. It is still unknown whether PET products can improve the accuracy of hydrological simulation, and how different resolutions and input types (lumped/distributed) of PET products affect the performance of hydrological models. The question about how hydrological models will be further developed in combination with PET products is also not well answered, given the complexity in interaction between ET and other water cycle variables. In this study, a modified Soil and Water Assessment Tool (SWAT) was chosen to examine the capability of PET products in improving hydrological simulation in terms of surface runoff, streamflow and baseflow, together with the Shaying River Basin in China as a case study. Two Moderate Resolution Imaging Spectroradiometer (MODIS) PET products were employed to form various PET scenarios. Results indicate that PET products are significantly different from the PET simulated by the SWAT built-in PET module in terms of spatial distribution and magnitudes. According to statistical metrics, the use of PET products to replace the SWAT built-in PET module can improve the accuracy of hydrological simulation compared with the original SWAT using its built-in PET module. Th