Impact of Eastern redcedar encroachment on stream discharge in the North Canadian River basin

Eastern redcedar (Juniperus virginiana L.) is a woody plant that is rapidly encroaching into the grasslands of states located in the US Great Plains. There is some concern that redcedar will adversely impact stream discharge in these water-limited areas through increased transpiration and canopy interception in comparison to that of grasslands. We conducted a modeling study in the central reach of the North Canadian River basin between Lake Canton and Lake Overholser, located in central Oklahoma. The North Canadian River supplies about 25% of Oklahoma City's water supply. After model calibration, we simulated redcedar encroachment into the study area's grasslands in 10% increments to assess impact on stream discharge. We also performed simulations that represented complete removal of redcedar from the study area. Our simulations suggested that if all grasslands in the study area were replaced by redcedar, the simulated reduction in stream discharge would equal 112% of current municipal water demand and 89% of the projected 2060 demand. However, a more realistic conversion of 20% of grassland to redcedar would, according to our simulations, reduce stream discharge by an amount of water equivalent to ≈ 27% of the current water demand, or ≈ 21% of the projected 2060 demand. Our model simulations suggest that encroachment of redcedar into grasslands could have a detrimental effect on stream discharge, which could impact water availability on populations further downstream.