A.J. Purdy

Postdoctoral Scholar | NASA Jet Propulsion Laboratory

Google Scholar

Hydrology - Water Resources - Ecosystems - Environment


I look to better understand the global water cycle including its relation to human activity, the environment, and the earth system.

Check out the site and please reach out if you see an opportunity to collaborate or would like to talk about any previous or ongoing projects, publications , teaching, or adventures.

Hydrology - Water Resources - Ecosystems - Environment

  • Hydrology - Evapotranspiration is a key climate variable that links the water, energy, and carbon cycles. Despite its importance in the earth system and water cycle, knowledge gaps still remain to improve both satellite-derived estimates and land surface models. During my dissertation, I analyzed the role of ground heat flux in inter-algorithm evapotranspiration uncertainty and improved global estimates of water and energy fluxes by incorporating soil moisture observations from the Soil Moisture Active Passive (SMAP) satellite into a widely-used evapotranspiration model (Purdy et al., 2016, Purdy et al., 2018). Recently, I have collaborated on studies exploring how models partition evapotranspiration into the components of soil evaporation, canopy transpiration, and evaporation of intercepted water on leaves (Massoud et al., in review, Talsma et al., 2018a, 2018b). Continued improvement and application of evapotranspiration models and datasets provide many avenues for future research. These include: the opportunity to close water budgets across watersheds and continental basins; predicting how changes in climate will impact evapotranspiration and thus future water yields from head-water catchments; and quantifying how forest fires or land use changes feedback on the water cycle by altering fluxes (infiltration, runoff, & evapotranspiration) critical for freshwater availability.
  • Water Resources - I am interested in how humans interact with the water cycle under a changing climate. Freshwater availability is critically important to support a growing population and large agriculture industry in California. Quantifying and understanding how changes in climate and human activity impact the local and regional water cycles creates an opportunity to support management of this precious resource. I have worked on projects using the Gravity Recovery and Climate Experiment (GRACE) satellites to measure how human management, such as groundwater extraction and reservoir diversion, impacts the water cycle in the Colorado River Basin and to projecting how changes in management strategy can buffer groundwater reliance in California under a changing climate (Castle et al., 2016; Massoud et al., 2018). In addition to quantifying human reliance on this precious resource, satellite observations also have the ability to support on-farm water management and mitigate the impacts from drought (Melton et al., 2012; Purdy et al., in prep). I plan to pursue projects that explore the human dimension of the water cycle to support societal needs.
  • Ecosystems & Environment - The terrestrial biosphere represents a very small part of earth yet plays an enormous role in Earth’s future climate by controlling fluxes of key energy, water and carbon cycle variables. The extent to which plants buffer the effects of hotter and drier conditions associated with drought ultimately dictates how these events and ecosystems feedback on weather, climate, and water availability. Two variables that quantify ecosystems’ functional response to stress are gross primary production (GPP) and evapotranspiration (ET). My recent research efforts combine multiple satellite observations and models to track how the environment and ecosystems respond to perturbations.



Conference Presentations

  • A.J. Purdy, J. Fisher, J. Kawata, G. Om, M. Reynolds, Z.M. Ali, J. Babikian, C. Roman, M. Sikka Oral Presentation AGU Fall 2018
  • J.S. Famiglietti, P.W. Liu, A. McEvoy, D.N. Wiese, J.T. Reager, A.J. Purdy, M. Rodell, C.H. David Food Grows where Groundwater Flows: California Grapples with Chronic Water Scarcity. Oral Presentation AGU Fall 2018
  • Purdy, A.J., Fisher, J., Goulden, M.L., Randerson, J.S., Famiglietti, J.S., Water vs. Carbon: An evaluation of SMAP soil moisture, evapotranspiration, & OCO-2 solar induced fluorescence to characterize global plant stress. Poster Presentation AGU Fall 2017
  • Purdy, A.J., Fisher, J., Famiglietti, J.S., Potential for SMAP soil moisture observations to improve remote sensing of evapotranspiration algorithms. Oral Presentation AGU Fall 2016
  • Purdy, A.J., Fisher, J., Famiglietti, J.S., Ground Heat Flux: What’s the best approach. Oral Presentation AGU Fall 2015
  • Castle, S., Reager, J.T., Thomas, B.F.,Purdy, A.J., Lo, M. H., Rodell, M., Famiglietti, J.S., Assessing the impacts of water management on evapotranspiration in the Colorado River Basin. H34D-06 AGU Fall 2014
  • Purdy, A.J., Famiglietti, J.S. Remote sensing and modeling evapotranspiration: A high-resolution multi-method comparison at point and basin scales in California. Oral Presentation AGU Fall 2013
  • Melton, F.S. Lund, C., Johnson, L., Michaelis, A., Pierce, L., Guzman, A., Hiat, S., Purdy, A.J., Rosevelt, C., Brandt, W., Votava, P., Nemani, R., Satellite Mapping of Agricultural Water Requirements in California with the Terrestrial Observation and Prediction System. H21H-1272 AGU Fall 2012
  • Purdy, A.J., Lund, C.P., Pierce, L., Melton, F.S., Guzman, A., Harlen, I., Holloway, R., Johnson, L., Lee, C., Nemani, R.. Applications of wireless sensor networks, soil water balance modeling, and satellite data for crop evapotranspiration monitoring and irrigation management support. H21F-120: Poster AGU Fall 2011
  • Melton, F., Johnson, L., Lund, C., Michaelis, A., Pierce, L., Guzman, A., Hiat, S., Purdy, A.J., Lee, C., Rosevelt, C., Fletcher, N., Votava, P., Milesi, C., Hashimoto, H., Wang, W., Scheffner, E.J., Nemani, R., Satellite Monitoring and Management Support in California with the Terrestrial Observation and Prediction System H21F-1227 AGU Fall 2011

White Papers

Teaching Experience

I have been fortunate to be involved in teaching at many levels throuhgout my academic career. Below I detail the university level courses I have been involved with. In addition to the courses I have received formal tutoring training from the Cal State System and taken a course in curiculum development and engaged learning from the University of California.


Remote Sensing and Hydrology

CUAHSI 2016/2017

I helped plan a three day workshop at BIOSPHERE 2 in Tuscon, AZ and CUAHSI headquarters in Boston, MA to review current and future NASA earth observing satellites that focus on the hydrologic cycle. We provided in depth presentations on the history and application of GRACE, SMAP, and the upcoming SWOT missions. The workshops included advising group projects focused on one of the NASA satellites.


Terrestrial Hydrology

UCI 2016

An introduction to the terrestrial water cycle. I helped formulate new course exercises and gave guest lectures. I was able to update assignments to incorporate real observations of precipitation, snowpack, streamflow, reservoir storage, and groundwater from across California to use within assignments focused on hydrologic theory.


Data Analysis for Earth Sciences

UCI 2015

Analysis and interpretation of geophysical data, including functional fitting, probability density functions, and multidimensional time-series methods, with applications in atmospheric, oceanic, and biogeochemical sciences.


Fundamental Processes in Earth and Environmental Studies

UCI 2014

An introduction to the physical environment, biological systems, and human-environment interactions. Explores physical principles such as fluid transport and reaction rates using environmental examples as well as principles of populations, ecosystems, carrying capacity, and sustainable use of resources.


Local and Regional Environmental Issues

UCI 2014

An introduction to common environmental issues using case studies from Orange County and California. Studies natural hazards as well as human-caused problems with air quality, water quality, coastal pollution, ecosystem degradation, and urban climate.


On Thin Ice

UCI 2014

Climate Change and the Cryosphere: Introduction of the basic science that governs the cryosphere and its interaction with the climate system. Covers some of the significant economic, sociological, and political consequences of the recent melting of the cryosphere driven by anthropogenic climate change.


Physics I

CSUMB 2011

Physics 1 explores Newtonian mechanics (including rotational motion), work, energy, power, mechanical waves and sound, and circuits – in other words, fundamental physics concepts.


Physics II

CSUMB 2011

Physics 2 explores fluid statics and dynamics, thermodynamics with kinetic theory, PV diagrams and probability, electrostatics, electrical circuits with capacitors, magnetic fields, electromagnetism, physical and geometric optics, and quantum, atomic, and nuclear physics. Lab Instructor

About Me

Welcome to my site. I am currently a postdoctoral scholar in the Carbon and Ecosystems Group at the NASA Jet Propulsion Laboratory.

Growing up in California, I have always been enamored with the outdoors. It wasn't until my senior year at University of San Diego that I realized I didn't want to be a manufacturing engineer. Subsequently, I forced my way into a CEQA course to fulfill an elective. That course set me on a path to explore and understand how humans and the environment interact.

At CSU Monterey Bay, I earned a MS in Coastal Watershed Science and Policy. During my time in Monterey, I worked with a team of NASA Ames scientists that applied satellite data sets to support on-farm management.

After my Masters, I headed to UC Irvine where earned a MS and PhD in Earth System Science under the advisement of Jay Famiglietti. At Irvine I honed my skills in remote sensing and geospatial analyses. My dissertation focused on advancing satellite-driven evapotranspiration algorithms and applying these estimates to link the carbon and water cycles from space.

Outside of work, I enjoy surfing, camping, and adventuring with my wife Katherine and dog Sully.


My contact information is listed at the top my CV. Contact me if you see an oportunity to colaborate or to chat science, education, or adventures.