Distributed memory parallel computing of three-dimensional variable-density groundwater flow and salt transport

Fresh groundwater reserves, being of vital importance for more than a billion of people living in the coastal zone, are being threatened by saltwater intrusion due to anthropogenic activities and climate change. High resolution three-dimensional (3D), variable-density (VD), groundwater flow and salt transport (FT) numerical models are increasingly being used to support water managers and decision makers in their strategic planning and measures for dealing with the problem of fresh water shortages. However, these computer models typically requir e long runtimes and large memory usage, making them impractical to use without parallelization. Here, we parallelize SEAWAT, and show that with ou r parallelization 3D-VD-FT modeling is now feasible for a wide range of hydro-geologists, since a) speedups of more than two orders of magnitude can be obtained as illustrated in this paper, and b) large 3D-VD-FT models are feasible with memor y requirements far exceeding single machine memory.