How do biogeochemical controls on rainforest photosynthetic water efficiency interact with regional atmospheric and hydrological dynamics over tropical rainforests? Former PhD student Meg Fowler led a collaborative paper in Nature Climate Change that represented the first attempt to couple runoff from climate models through hydrodynamic streamflow models in experiments that isolate the effect of CO2 fertilization on plant physiology. This provoked that plant physiology, not warming, is a greater control on future streamflow changes in most watersheds equatorward of 35 degrees latitude, increasing the efficiency of runoff. Meanwhile in Langenbrunner et al. (2019) we have worked towards unraveling the causality and regional atmospheric dynamics that mediate these simulated responses. This has shown that parameterized planetary boundary layer turbulence feedbacks, which lead to rapid vertical mixing in response to rainforest surface forcing, play a major role in modifying lateral flows of vapor that underpin the overall rainforest response to CO2 fertilization. We remain interested in deepening analysis of these interactions in the context of finer scale processes and deforestation dynamics in the coming years.

I have branched out to study the land-atmosphere interface at UCI. In 2016, together with my second postdoc J. Sun, I published the first comprehensive analysis of the effects of explicit convection (SP) on simulated global land-atmosphere coupling [24]. This revealed several improvements relative to standard GCMs in the form of reduced hydrologic coupling intensity. My second PhD student, H. Qin, published a 2018 follow-on study that examined thermal terrestrial coupling, which has also revealed a puzzling systematic increase in the Bowen Ratio linked to the use of SP [29]. Most recently I have become quite interested in the effects of stomatal conductance (leaf pores closing due to elevated CO2), thanks to a new collaboration with the Randerson group in our department, facilitated by my former postdoc G. Kooperman. In a 2018 Nature Climate Change paper led by Kooperman and Randerson, we show that these physiologically induced changes to plant water use efficiency have profound atmospheric consequences over tropical rainforests that rival the radiative effects of CO2 in producing rainfall changes in future climate [31]. As part of this work, I wrote a gross moist stability analysis supplement, which implicated the role of lateral vapor export above the Amazonian planetary boundary layer in the dynamics; this is now the focus of a new co-advised postdoc project. I continue to grow in this direction — related work will form the second chapters of two of my current PhD students’ dissertations, who have also become interested in the forest physiological effect and regional scale Amazon atmospheric dynamics.