PS 4-37
Rangeland transition and its potential impact on water resources in the South-Central Great Plains
Rangelands are an important land use in the south-central Great Plains and usually occupy the upland or marginal areas with row crops occupying the lowland and fertile areas, forming a mosaic landscape. These rangelands are under rapid encroachment of woody plants, primarily by an evergreen juniper species (Juniperus virginiana,eastern redcedar) since the 1970s. It is unknown how this land cover change, if unconfined, will alter basin level water budget. We simulated the impact of woody plant invasion into rangelands on streamflow and groundwater recharge dynamics for the lower Cimarron River Basin using the Soil and Water Assessment Tool (SWAT) model. We simulated a land cover scenario where current rangeland was completely converted to juniper woodland while the other land uses remained unchanged and resultant changes in streamflow and groundwater recharge over a time period of 22 years (1988-2009).
Results/Conclusions
The model suggests that: (1) heavier encroached sub-basins could have up to 70 mm higher evapotranspiration (ET) loss and a resultant 80 mm lower water yield annually. (2) Surface runoff reduction dominates the water yield reduction in spite of slight compensation from increased baseflow. (3) Although runoff declines proportionally to the gradual increase of redcedar coverage, linear and non-linear trends emerge respectively for the wet and dry sub-basins across the hydro-climate transitional zone. Due to increased ET year round, streamflow in the Cimarron River is predicted to be lower throughout the year with more severe reduction up to 60% in summer months.