Deep drainage sensitivity to climate, edaphic factors, and woody encroachment, Oklahoma, USA

Abstract

Because groundwater is Earth's largest pool of freshwater, understanding the sensitivity of deep drainage to climate, soils, and land cover is critical in managing water resources. To better understand controls on this critical flux in the context of woody encroachment, we determined the sensitivity of deep drainage to climate, soil texture, soil compaction, rooting depth, growing season duration, and plant-water stress response using Hydrus-1D to simulate deep drainage. To evaluate the simulation results, we compared these results with ground measurements at two anchor sites. At both anchor sites, Hydrus-1D predictions of deep drainage matched measured values within the errors inherent in ground measurements. Sensitivity analysis suggested greatest sensitivity of deep drainage to climate (24 mm yr À1 ) and rooting depth (12 mm yr À1 ), moderate sensitivity to growing season duration (5 mm yr À1 ) and soil texture (4 mm yr À1 ), and lowest sensitivity to topsoil compaction and plant-water stress response (3 mm yr À1 ). The sensitivity analysis indicated the relative importance of the plant-related factors considered, which, in decreasing order, were rooting depth, growing season duration, and plant-water stress responsefactors that change concomitantly as a result of forestation or woody encroachment. Further ground-truth measurements of woody encroachment effects on deep drainage are needed to confirm or refine the results of this simulation modelling study.

Recent Developments and Applications of the HYDRUS Computer Software Packages

“…Similarly, changes in groundwater recharge in response to the expansion of rainfed cultivation in the Sahel, West Africa, were evaluated by Ibrahim et al (2014). Another related application is to anticipate the sensitivity of groundwater recharge to changes in climate in response to greenhouse effects (e.g., Leterme et al, 2012; Newcomer et al, 2014; Pfletschinger et al, 2014; Wine et al, 2015). Additional applications of HYDRUS for evaluating groundwater recharge are given below in the Groundwater Recharge Applications section and on the HYDRUS website.…”

In ecoregions across western USA streamflow increases during post-wildfire recovery

“…However, in addition to effecting modifications to climate forcings used in conventional physically based hydrologic predictions, climate change also effects ecological disturbances; these climatic controls on ecological disturbance may in turn be amplified by other components of global change (Dale et al 2001, Scheffer et al 2001. Widespread upland global change-induced ecological disturbances include woody encroachment (Van Auken 2000, Wine et al 2015), tree mortality due to pest-pathogen complexes (Kurz et al 2008), and wildfire (Westerling et al 2006). Assuming that these ecological disturbances can substantially influence Earth's future water balance, they represent structural uncertainties in the current approach to projecting future water resource availability.…”

“…Following the initial disturbance, the formerly forested system may be colonized by herbaceous plants having different functional traits than coniferous forest stands. During this vegetation recovery phase-conventionally referred to as secondary succession-shallower rooting depth and shorter growing season duration (in that order of importance) of herbaceous plants relative to evergreen trees may increase groundwater recharge, depending on interactions with transient climate (Wine et al 2015). Additionally, enhanced post-wildfire preferential flow may serve as another mechanism increasing groundwater recharge following wildfires (Stoof et al 2014).…”

Climate moderates potential shifts in streamflow from changes in pinyon‐juniper woodland cover across the westernU.S.

“…Therefore, despite the importance of soil factors in controlling Δ ET tree‐grass , climate is likely even more important than subsurface characteristics. Confirming the greater importance of climate compared to soil characteristics, Wine, Hendrickx, Cadol, Zou, and Ochsner () demonstrated that climate was more important than soil available water and rooting depth in determining deep drainage.…”