Abstract
Watershed characteristics such as patterns of land use and land cover (LULC), soil structure and river systems, have substantially changed due to natural and anthropogenic factors. To adapt hydrological models to the changing characteristics of watersheds, one of the feasible strategies is to explicitly estimate the changed parameters. However, few approaches have been dedicated to these non-stationary conditions. In this study, we employ an ensemble Kalman filter (EnKF) technique with a constrained parameter evolution scheme to trace the parameter changes. This technique is coupled to a rainfall-runoff model, i.e., the Xinanjiang (XAJ) model. In addition to a stationary condition, we designed three typical non-stationary conditions, including sudden, gradual and rotational changes with respect to two behavioral parameters of the XAJ. Synthetic experiments demonstrated that the EnKF-based method can trace the three types of parameter changes in real time. This method shows robust performance even for the scenarios of high-level uncertainties within rainfall input, modeling and observations, and it holds an implication for detecting changes in watershed characteristics. Coupling this method with a rainfall-runoff model is useful to adapt the model to non-stationary conditions, thereby improving flood simulations and predictions.
Highlights
Watershed characteristics, which determine hydrological processes, have been significantly reshaped by climate change and human activities [1]
The ensemble Kalman filter (EnKF)-based method with a constrained perturbation for model parameters suggests that the parameter travel can be traced under stationary and non-stationary conditions
Model parameters can change in response to the evolution of watershed characteristics
Summary
Watershed characteristics, which determine hydrological processes, have been significantly reshaped by climate change and human activities [1]. Climate warming and extreme events have led to the gradual melting of glaciers, the shift of vegetation succession and the reconstruction of soil structure and soil biology [2,3,4,5] Human activities, such as urbanization, deforestation, agricultural planting and infrastructure development substantially alter land use and land cover (LULC) from watershed to regional scales [6,7,8,9,10]. To pursue reliable simulations or predictions, the hydrology community has developed a large number of sophisticated hydrological models of either a physical or a conceptual physical type The frameworks of these models are constructed based on mathematical descriptions of the underlying physical processes, and model parameters are defined to describe the specific physical characteristics regarding the LULC, soil properties and river systems. Even the parameters of a conceptual hydrological model define key relationships between rainfall and runoff in a spatially aggregated manner, these relationships are associated with the underlying watershed characteristics [1]
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