Surface-groundwater Interactions in California
Agriculture in the California Central Valley is only possible through irrigation. Currently, we are pumping more groundwater for irrigation than is being replaced via recharge to underground aquifers. In order to sustainably manage groundwater resources, we need to quantify the sources of groundwater recharge. Current water management tools, like those from the USGS, make crude estimates of recharge coming from the Sierra Nevada mountains. In this project, I built an integrated land surface-groundwater model for the southern Central Valley to investigate sources of groundwater recharge. Then, we worked with researchers from UC Davis and the Scripps Institution of Oceanography to develop downscaled climate change predictions to study the impact of climate change and groundwater pumping on aquifer management.
Ecohydrology of semiarid catchments with woody plant encroachment
Drylands cover about 40% of the Earth surface and have been dramatically changed by woody plant encroachment over the last 150 years. Caused by a combination of over-grazing, fire suppression, and climate change, the encroachment of woody shrubs into native grasslands has large effects on the ecology and hydrology of huge parts of the world. The impact of the two global phenomenon, woody plant encroachment and climate change, on water resources is a key problem that scientists need to address. In this project, I performed field experiments and collected data in two research watersheds to explore the impact of climate and vegetation change on groundwater resources.
We used the data collected to build a new conceptual model for how groundwater recharge can occur in drylands. Because drylands are water limited, previous research had shown that plants were able to use all of the water in the soils and prevent water from recharging underground aquifers. We found that heavy rainfall (P) never infiltrated into the soils, instead becoming sheetflow that ran off the soil surface and reached the streambed. Since the desert streambeds were sandy, water was able to infiltrate quickly and potentially become focused groundwater recharge.
Finally, we used computer models built around the data collected to test how shrub encroachment and climate change might impact water recharging groundwater aquifers. We found that the larger rainfall events predicted by climate change models would increase groundwater recharge at the expense of plant available water. This would likely support more shrub encroachment, which also was found to increase recharge at the expense of plant available water, in a positive feedback loop.