Assessment of climate change impact on floodplain and hydrologic ecotones

SummaryCurrent modeling efforts continue to indicate that the effects of climate change will be both global and local in scale, and that ecohydrologic factors including vegetation pattern, altered precipitation events, reduced system yields due to streamflow changes, increased flooding and changes to current floodplain characteristics will be affected. Therefore, using technology such as light detection and ranging (LiDAR) data, using future general circulation model (GCM) data, and conducting floodplain analyses to predict the changes to ecohydrologic factors are critical for cataloging existing ecosystem resources and for understanding the effects that different climate change scenarios may have on these resources at the basin scale. This study considers the effects of three different GCM climate change emissions scenarios (high from the IPSL GCM’s A2 scenario, middle from the ECHAM5 GCM’s A2 scenario and low from the GISS GCM’s B1 scenario) using daily downscaled precipitation and temperature data over the Lower Tualatin basin in the Pacific Northwest US. The Tualatin River basin is a dynamic watershed that supports urban and agricultural uses and is also 50% forested. Its economic drivers include agricultural and forest products, as well as other consumer products including high-tech software and hardware industries. The Soil and Water Assessment Tool (SWAT) software was used as a distributed hydrologic model to predict the daily flows in the basin. It is predicted the 50-year recurrence interval (RI) flow will decrease significantly for the low and middle emissions scenarios (to between approximately 18,000–19,000 cfs compared to the observed 50-year RI of near 26,000 cfs) and will increase significantly under the high emissions scenario to nearly 33,000 cfs. Floodplain extents for the various climate scenarios and timeframes were delineated using the HEC-RAS model. A geo-processing procedure was employed to delineate hydrologic ecotones to evaluate the condition of riparian areas and streams. A current and future conditions analysis was performed using the combination of aerial imagery and LiDAR data for the vegetation within the ecotones in order to: (1) provide an existing inventory of vegetation within the basin and (2) to predict the effects that climate change may have on vegetation within the basin.

Research highlights
► Studies the Tualatin River in the Pacific Northwest, US to predict the impact of climate change on ecohydrologic parameters.
► Results show increased future storm flows based on current emissions trends.
► Significant impacts to hydrologic ecotones and LiDAR-derived vegetative features is anticipated.