One area of her research focuses on the exchange of water between plants and the atmosphere. She uses stable isotopes of liquid water and water vapor in the atmosphere to identify spatial and seasonal variability in plant source water and atmospheric moisture, and to partition evapotranspiration into soil evaporation and plant transpiration. Her interests also include using carbon and oxygen isotopes of plant organic matter (e.g; tree rings) to measure leaf-level physiological responses to changing environmental conditions. Welp earned her Ph.D. in Environmental Science and Engineering at the California Institute of Technology.