EGU General Assembly 2020
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Short and long-term analyses of plant greenness and evapotranspiration dynamics in the riparian zone of the Colorado River Delta before and after the 2014 Minute 319 environmental pulse flow

Pamela Nagler1, Armando Barreto-Muñoz2, Kamel Didan2, Christopher Jarchow2, Sattar Chavoshi Borujeni3, Hamideh Nouri4, Stefanie Herrmann5, and Martha Gómez-Sapiens6
Pamela Nagler et al.
  • 1U. S. Geological Survey, Southwest Biological Science Center, Tucson, AZ, United States of America (
  • 2University of Arizona, Biosystems Engineering, Tucson, AZ, USA
  • 3Soil Conservation and Watershed Management Research Department, Isfahan Agricultural and Natural Resources Research and Education Centre, AREEO, Isfahan 19395-1113, Iran
  • 4Soil Conservation and Watershed Management Research Department, Isfahan Agricultural and Natural Resources Research and Education Centre, AREEO, Isfahan 19395-1113, Iran
  • 5University of Arizona, School of Natural Resources and the Environment, Tucson, AZ, USA
  • 6Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ, 85721 USA;

Our study assessed the effects of ecological environmental flows from one nation to another, using remote sensing.  Remote sensing approaches to plant water use quantification can inform binational, integrated water resources management.  We provide plant water use estimates to plan for allocation of water in the Colorado River in USA and Mexico. Our study examined multi-year effects of a 2014 historically important binational experiment (the Minute 319 agreement of a water treaty between the U.S. and Mexico) on vegetative response along the riparian corridor for the years following the pulse flow which began in 2014.  We divided our study area into seven reaches and used remotely sensed imagery to exam vegetation greenness and plant water use or evapotranspiration (ET, the loss of water through evaporation from the instruments, the 250 m Moderate Resolution Imaging Spectroradiometer (MODIS) and 30 m Landsat 8 OLI satellite imagery to track ET and several vegetation indices to estimate the greenness of vegetation (e.g., NDVI, scaled NDVI, EVI, EVI2).  The Minute 319 environmental flow produced a 17% increase in VI (“Greenness”) as detected with Landsat throughout the riparian corridor in 2014.  The significant greening up was observed across reaches within the riparian zone, as well as in the non-inundated outer parts of the riparian floodplain, where groundwater supported existing vegetation.  However, after just two years (by the end of 2016) there was a 22% decrease in VI throughout the riparian corridor.  In 2017, an annual overall increase of 2% in greenness was calculated, before falling again, by 8%, over the year 2018.  From 2015-2018, the initial post-pulse greenup and ET as measured by Landsat (30m) & MODIS (250m) steadily declined, falling below pre-pulse levels in all reaches.  The VI response becomes bimodal and disintegrates after 2016 in all reaches except for in Reach 4, the restoration zone.  Our longer time-series analysis from 2000-2019 showed an overall increase in VIs (higher Greenness) and ET (more water loss) in the year of the 2014 pulse and in the year, 2015.  The higher VI and ET indicate that there was enough water in the riparian zone to generate a positive response from plants.  These results reversed a decline in VI and ET since the last major flood in 2000, but the effect did not last after the first couple of years after the pulse flow.  Our longer-term data results from 2000 through 2019 (approximately the last 20 years), showed that Landsat EVI (Greenness) declined 34% and ET (mm/day) declined 38% and since the 2014 Pulse Flow through 2019, Landsat EVI (Greenness) declined 20% and ET (mm/day) declined 23%.  The pulse flow in 2014 contributed enough water to slow the declines by almost two-thirds.  Added in-stream water helped native and invasive riparian species in terms of stand structure, extent and greenness but only for the very short-term.  Our results support the conclusion that the Minute 319 environmental flows from the U.S. to Mexico had a positive, but short-lived (one or two year), impact on vegetation growth in the delta. 

How to cite: Nagler, P., Barreto-Muñoz, A., Didan, K., Jarchow, C., Chavoshi Borujeni, S., Nouri, H., Herrmann, S., and Gómez-Sapiens, M.: Short and long-term analyses of plant greenness and evapotranspiration dynamics in the riparian zone of the Colorado River Delta before and after the 2014 Minute 319 environmental pulse flow , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5932,, 2020

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  • CC1: Comment on EGU2020-5932, Stenka Vulova, 07 May 2020

    Nice study - I am also working on estimating evapotranspiration with remote sensing data, but for urban vegetation. I am curious about the VI-based ET equation. Can other vegetation indices besides EVI be used? Where does the equation come from?

    I saw another VI ET equation in this session (Carpintero et al.), ET = (Kcb*Ks + Ke)ET0, where Kcb is based on VIs. Are there a few standard or 'most common' VI-based ET equations?

    • AC1: Reply to CC1, Pamela Nagler, 07 May 2020

      hi there, 

       Great question and would like to talk more to you using my email: (the session was 1-4  in the morning for me here in Arizona and I fell asleep with my new 3 month old baby and missed the great session).  

      Here are several papers but the Glenn et al 2010 is the best to explain why we are using this equation, which I published first in 2005 in Remote Sensing of Environment and refined in 2013.  I have included those citations too.  We definitely are seeing it's usefulness in urban areas and papers by Hamideh Nouri, myself and others have applied this equation successfully.  Using EVI2 (2-band) is an improvement over NDVI and simple to apply.  


      Glenn, E. P., Huete, A. R., Nagler, P. L., & Nelson, S. G. (2008). Relationship between remotely-sensed vegetation indices, canopy attributes and plant physiological processes: what vegetation indices can and cannot tell us about the landscape. Sensors, 8(4), 2136–2160.

      Glenn, E. P., Morino, K., Didan, K., Jordan, F., Carroll, K. C., Nagler, P. L., Hultine, K. R., Sheader, L., & Waugh, J. W. (2008). Scaling sap flux measurements of grazed and ungrazed shrub communities with fine and coarse-resolution remote sensing. Ecohydrology 1(4), 316-329.

      Glenn, E. P., Nagler, P. L., & Huete, A. R. (2010). Vegetation Index Methods for Estimating

      Evapotranspiration by Remote Sensing. Surveys in Geophysics, 31(6), 531-555.


      Glenn, E. P., Neale, C. M. U., Hunsaker, D. J., & Nagler, P. L. (2011). Vegetation index‐based crop coefficients to estimate evapotranspiration by remote sensing in agricultural and natural ecosystems. Hydrol. Process., 25, 4050-4062.

      Nagler, P. L., Cleverly, J., Glenn, E., Lampkin, D., Huete, A., & Wan, Z. (2005a). Predicting

      riparian evapotranspiration from MODIS vegetation indices and meteorological data.

      Remote Sensing of Environment, 94(1), 17-30.

      Nagler, P. L., Scott, R. L., Westenburg, C., Cleverly, J. R., Glenn, E. P., & Huete, A. R. (2005b). Evapotranspiration on western U.S. rivers estimated using the Enhanced Vegetation Index from MODIS and data from eddy covariance and Bowen ratio flux towers. Remote Sens. Environ., 97(1), 337–351. doi:10.1016/j.rse.2005.05.011

      Nagler, P. L., Glenn, E. P., Nguyen, U., Scott, R. L., & Doody, T. (2013). Estimating Riparian and Agricultural Actual Evapotranspiration by Reference Evapotranspiration and MODIS

      Enhanced Vegetation Index. Remote Sensing, 5, 3849-3871.

      For Urban environments, see the papers by Hamideh Nouri, this one in 2014 was the first I collaborated with her on, but we have others since, one coming out this week in Hydrological Processes!

      And remotesensing2014_6_580-602_Hamideh Nouri and three others

      • AC2: Reply to AC1, Hamideh Nouri, 07 May 2020

        Pamela and Stenka

        I take this opportunity to introduce you, two. @ Stenka, Pamela is my mentor and inspiration in the last 8 years. I wanted to introduce you to Pam last year at EGU but you had to leave early because of the fieldwork. @Pam, you know Stenka from my emails and the potential to check energy-based approaches for UGS. She is the bright PhD student from TU Berlin that I'm collaborating with. Part of her PhD is on the ET of UGS.

      • CC2: Reply to AC1, Stenka Vulova, 07 May 2020

        Nice to meet you and thank you for the kind introduction Hamideh! I may apply this method in my work as well. I will save your response as a reference, and the recommended literature is very helpful.