This month, we are pleased to interview Angela J. Rigden, who is a fifth-year Ph.D. student at Boston University.  Her dissertation research is focused on detecting and attributing multi-decadal trends in evapotranspiration over the continental United States (see below for details).  Angela is planning to defend her dissertation this summer.  To know more about Angela, please see her personal website and Researchgate profile.

Please tell us about yourself

My passion for scientific research began while studying engineering at Cornell University.  During my freshman year, I joined Cornell’s Soil and Water Lab under the supervision of Todd Walter and worked in the lab until graduation.  While working in the lab, I realized my strengths in modeling and data analysis and my interest in ecohydrology.

After graduating from Cornell, I began graduate school at Boston University working with Guido Salvucci.  A large portion of my Ph.D. has been spent developing a model that estimates evapotranspiration from data collected at common weather stations.  I was first introduced to AmeriFlux data as a means to validate this model, but quickly started utilizing the flux data to answer other questions on land surface processes.

Outside of research, I enjoy surfing, hiking, and visiting my home state of Missouri.

Please tell us about your recent studies. What’s the main take-home message? or, what’s exciting about the study?

Guido and I recently published a paper in Global Change Biology (Rigden and Salvucci, 2017) on detecting and attributing trends in summertime evapotranspiration (ET) across the US from 1961 to 2014.  To estimate ET at this temporal and spatial resolution, we utilized the Evapotranspiration from Relative Humidity at Equilibrium (ETRHEQ) method (Rigden and Salvucci, 2015).  In the ETRHEQ framework, ET is estimated using an emergent relationship between the diurnal cycle of the relative humidity profile and the surface conductance.

After estimating ET at 236 weather stations from 1961 to 2014, we identified spatial patterns in the ET trends across the US and attributed these patterns to potential drivers (meteorological, radiative, and/or surface properties).  From the late 1990s to 2014, we found a relatively spatially uniform decline in summertime ET across the US.  Our results suggest that this decline is primarily due to declines in surface conductance.  To identify the mechanism limiting the surface conductance, we utilized satellite-derived estimates of NDVI and soil moisture and the Farquhar/Ball-Berry stomatal conductance model.  Results of this analysis suggest that declines in surface conductance (and thus, ET) since the late 1990s are consistent with declines in stomatal conductance induced by increasing vapor pressure deficit.  These results highlight the importance of stomata in modulating trends in ET.

As you work more with flux data (e.g., AmeriFlux), what skills do you feel you need to acquire (either in the past or near future) to make your studies more effective?

Good programming and data management skills are very useful when processing and analyzing flux data.  I learned to use Matlab as an undergraduate and this skill has been invaluable as a graduate student.  I feel that maintaining clean, commented scripts and publishing reproducible methods are essential when developing models and using flux data.

As I look to the future, I hope to get more involved with data collection and collaborate with PIs at the AmeriFlux sites.  I feel that learning instrumentation skills will give me a deeper understanding of the strengths and limitations of the data, making my studies more effective.

Who have been your mentors and how have they helped you arrive at where you are today?

Guido Salvucci’s mentorship has been pivotal to my success as a graduate student and scientist.  In addition to teaching me the technical and theoretical underpinnings of my research, he has encouraged me to explore my curiosities.  I am always learning from Guido, and am very thankful for his mentorship as an advisor.  My committee members (Mark Friedl, Nathan Phillips, and Mike Dietze) have also been essential to my graduate research, helping me shape my ideas into a thorough, cohesive dissertation.  I am also grateful for the mentorship of Dan Li, who has guided me to pose focused research questions, think about processes mathematically, and better understand boundary layer dynamics.  As an undergraduate, Todd Walter’s mentorship was above and beyond, and I would not be where I am today without his guidance.  Todd encouraged me to develop my own, independent research projects and apply for fellowships, including a successful NSF-GRFP.  In my experience, getting as involved as possible with research while an undergraduate is a huge advantage to anyone seeking a graduate degree.

What resources do you think the flux networks or communities (e.g., Ameriflux, Fluxnet) have provided or could potentially provide to help your studies or career?

Thus far, I have primarily used the Level-2 AmeriFlux data.  The diversity of sites allow for comprehensive analyses and validation across climates, plant functional types, and energy/water limitations.  I thank all of the principle investigators for sharing their data and making this research possible.  In the future, I am eager to analyze the dataset as it grows through time, specifically characterizing interannual variability and trends in observed surface fluxes, and the sources of these variations.

What are your career goals and aspirations?

I will be graduating this summer with a Ph.D. in Earth Science and a Certificate in Biogeoscience.  I am currently looking for a postdoctoral position modeling land surface processes.  I am eager to focus my research on new processes in the soil-vegetation-atmosphere continuum to complement my knowledge of water/energy fluxes.  Long-term, I hope to stay in academia.

In addition to my scientific research, I am also passionate about educating and encouraging kids to STEM fields.  Currently, I help run a weekly afterschool program for elementary aged girls at a Boy and Girls Club in Boston.  As I advance in my career, I also hope to develop programs connecting academia with primary education.

— Texts and Photos are provided by Angela Rigden —


Rigden, A. J., and G. D. Salvucci (2017), Stomatal response to humidity and CO2 implicated in recent decline in US evaporation, Global Change Biology, 23(3), 1140–1151, doi:10.1111/gcb.13439.

Rigden, A. J., and G. D. Salvucci (2015), Evapotranspiration based on equilibrated relative humidity (ETRHEQ): Evaluation over the continental U.S, Water Resour. Res., 51(4), 2951–2973, doi:10.1002/2014WR016072.

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