Understanding the spatio-temporal characteristics of soil moisture and subsurface flow processes at the catchment-scale involves the use of many different types of data, such as field measurements, remote sensing images, digital elevation models, and results from hydrological simulation. All of these data types have a strong geographic component, so it is natural to consider geographic information systems (GIS) as a primary tool for data organization and analysis. However, current GIS have numerous limitations which make them incapable of completely supporting the needs of this type of hydrological research. In this paper we argue that some of the important weaknesses of GIS are the very strengths of scientific visualization, and that a natural solution is to combine or integrate these two types of systems. The strengths and weaknesses of GIS and scientific visualization systems will be discussed, and a case study of integration, using tools that are available today, is presented for an application involving hydrological modelling.