It is important to note that applying the model with calibrated parameters from one watershed to a different watershed can degrade the model performance and thus is not to be recommended. In this way, the calibrated parameters reflect all the unique characteristics of that watershed in an aggregated way. Because model errors can depend on many things, such as the watershed characteristics, hydrological models are often calibrated for each individual watershed. It has been a regular practice for most if not all hydrological models. Model calibration serves as a way to minimize model errors that might be associated with model structural uncertainty, model resolution, and the crude representation of physical processes in model parameterizations. An important step in using hydrological models is to calibrate the models by adjusting model parameters so that the models can simulate observed hydrological quantities such as streamflow in a reasonably accurate way. These hydrological models are very useful tools for understanding the pathways that LULC affects streamflow, but they are still a very simplified representation of the real world. The use of physically based distributed hydrological models such as SWAT and VIC has been gaining popularity in recent years, and is considered as an effective way to simulate the complex hydrological processes and to quantify the impact of LULC changes on those processes. (2016) employed the VIC hydrological model to evaluate the comparative effects of climate and land cover changes on hydrological responses of the Muskeg River in Alberta, Canada. Moiwo & Tao (2014) studied the effects of land use change on groundwater recharge and discharge in a semi-arid area in northeast China using an integrated recharge–discharge model. (2011) used the Soil and Water Assessment Tool (SWAT) model to assess land use and climate change impacts on the hydrology of the upper Mara River basin, Kenya. (2010) applied the Generalized Additive Model to quantify the impact of LULC changes on the discharge in the upper Mississippi River. The approaches for studying the impact of LULC changes on hydrological processes typically involve multivariate statistics and hydrological modeling. However, the shrinkage of woodland is the main driving force that decreases the soil water, thus contributing to a small increase in streamflow during the dry season. ![]() Results indicate the following: (1) time-varying parameters’ calibration is effective to ensure model validity when dealing with significant changes in underlying land surfaces (2) LULC changes have significant impacts on the watershed streamflow, especially on the streamflow during the dry season (3) the expansion of cropland is the major contributor to the reduction of surface water, causing decline in annual and dry seasonal streamflow. The spatiotemporal impacts of LULC changes on watershed streamflow are quantified, and the mechanism that connects the changes in runoff generation and streamflow with LULC is explored. ![]() To accurately simulate the hydrological process for a watershed like the Wei River Basin, where the surface characteristics are highly modified by human activities, we present an alternative approach of time-varying parameters in a hydrological model to reflect the changes in underlying land surfaces. ![]() It is critically important to quantify the impact of land use land cover (LULC) changes on hydrology, and to understand the mechanism by which LULC changes affect the hydrological process in a river basin.
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