Landscape changes and their hydrologic effects : interactions and feedbacks across scales

Human activities have extensively altered landscapes throughout the world and further changes are expected in the future. Anthropogenic impacts such as land use change, groundwater extraction and dam construction, along with the effects of climate change, interact with natural factors including soil weathering and erosion. Together, these processes create a constantly shifting, dynamic terrestrial environment that violates the assumption of stationarity commonly applied in hydrology. Consequently, hydrologists need to rethink both statistical and calibrated models to account for complex environmental processes. We review the literature on human-landscape-hydrological interactions to identify processes and feedbacks that influence water balances. Most of the papers covered consider only a few of these processes at a time and focus on structural attributes of the interactions rather than the short and long-term dynamics. We identify challenges in representing the scale-dependence, environmental connectivity and human-water interactions that characterize complex, dynamic landscapes. A synthesis of the findings posits connections between different landscape changes, as well as the associated timescales and level of certainty. A case study explores how different processes could combine to drive long-term shifts in catchment behavior. Recognizing that some important questions remain unaddressed by traditional approaches, we suggest the concept of ‘big laboratories’ in which multifaceted experiments are conducted in the environment by artificially inducing landscape change. These experiments would be accompanied by mechanistic modeling to both untangle experimental results and improve the theoretical basis of environmental models. An ambitious program of physical and virtual experimentation is needed to progress hydrologic prediction for dynamic landscapes.