A Note of Caution Regarding the Interpretation of Hydrological Model Predictions under Climate and Anthropogenic Driven Changes
Abstract
We have conducted a series of numerical experiments to determine the connection between streamflow fluctuations at the outlet of large-scale watersheds (> 1000 km2) and hillslope scale (~ 0.1 km2) runoff signals that cast doubt on the interpretation of the hydrological meaningfulness of the representation of small-scale processes in hydrological models. We have used a distributed hydrological model that discretizes the landscape into small hillslope control volumes that are interconnected by the full extent of the river network of the Cedar River basin (~17,000 km2). We have created a set of forcing signals that are significantly different from each other but share the same volume of water being injected into the hillslope surface. Our results show that signals that are very different at the hillslope scale result in streamflow fluctuations at large scales that are indistinguishable from each other. Each of the signals can be interpreted as the output of a complicated set of hillslope-scale equations describing the rainfall-runoff transformation. This implies that the ability to reproduce hydrographs at the outlet of a large basin is not a reliable indication of the correctness of the description of small-scale processes controlling runoff production that include the description of vegetation, soil-types, land use practices, etc. Our results raise a red flag to any diagnostic study of changes in the streamflow under future scenarios of changing climate or anthropogenic modifications that use calibrated hydrological models, because the calibration process is a way of enforcing a match between input rainfall volumes to output runoff volumes even when the equations and parameters may not represent the true processes occurring in nature. Although our results would need to be generalized to include a more realistic version of routing in the river network, we believe that the space-time averaging process imposed by the random self-similar network draining the landscape blurs any meaningful connection between small-scale hydrological processes and large-scale streamflow fluctuations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H35D1065F