SERGHEI v2.0: introducing a performance-portable, high-performance, three-dimensional variably saturated subsurface flow solver (SERGHEI-RE)

Abstract. Advances in high-performance parallel computing have significantly enhanced the speed of large-scale hydrological simulations. However, the diversity and rapid evolution of available computational systems and hardware devices limit model flexibility and increase code maintenance efforts. This paper introduces SERGHEI-RE, a three-dimensional, variably saturated subsurface flow simulator within the SERGHEI model framework. SERGHEI-RE adopts the Kokkos-based portable parallelization framework of SERGHEI, which facilitates scalability and ensures performance portability on various computational devices. Moreover, SERGHEI-RE provides options to solve the Richards equation (RE) with iterative or non-iterative numerical schemes, enhancing model flexibility under complex hydrogeological conditions. The solution accuracy of SERGHEI-RE is validated using a series of benchmark tests, ranging from simple infiltration problems to practical hydrological, geotechnical, and agricultural applications. The scalability and performance portability of SERGHEI-RE are demonstrated on a desktop workstation, as well as on multi-CPU and multi-GPU clusters, indicating that SERGHEI-RE is an efficient, scalable, and performance portable tool for large-scale subsurface flow simulations.