Remote sensing vegetation index methods to evaluate changes in greenness and evapotranspiration in riparian vegetation in response to the Minute 319 environmental pulse flow to Mexico

Pamela L Nagler,Edward P Glenn,Christopher J Jarchow

doi:10.5194/piahs-380-45-2018

Abstract

Abstract. During the spring of 2014, 130 million m3 of water were released from the United States' Morelos Dam on the lower Colorado River to Mexico, allowing water to reach the Gulf of California for the first time in 13 years. Our study assessed the effects of water transfer or ecological environmental flows from one nation to another, using remote sensing. Spatial applications for water resource evaluation are important for binational, integrated water resources management and planning for the Colorado River, which includes seven basin states in the US plus two states in Mexico. Our study examined the effects of the historic binational experiment (the Minute 319 agreement) on vegetative response along the riparian corridor. We used 250 m Moderate Resolution Imaging Spectroradiometer (MODIS), Enhanced Vegetation Index (EVI) and 30 m Landsat 8 satellite imagery to track evapotranspiration (ET) and the normalized difference vegetation index (NDVI). Our analysis showed an overall increase in NDVI and evapotranspiration (ET) in the year following the 2014 pulse, which reversed a decline in those metrics since the last major flood in 2000. NDVI and ET levels decreased in 2015, but were still significantly higher (P < 0.001) than pre-pulse (2013) levels. Preliminary findings show that the decline in 2015 persisted into 2016 and 2017. We continue to analyse results for 2018 in comparison to short-term (2013–2018) and long-term (2000–2018) trends. Our results support the conclusion that these environmental flows from the US to Mexico via the Minute 319 “pulse” had a positive, but short-lived (1 year), impact on vegetation growth in the delta.

Highlights

In 2012, Minute 319 to the 1944 Treaty was signed allowing for a pulse flow of water into the Colorado River’s delta, in Mexico
Our study assessed the effects of water transfer via ecological environmental flows from one nation to another, using remote sensing of vegetative response
The most intense greening in 2014 took place in the zone of inundation by the pulse flow, but increases in normalized difference vegetation index (NDVI) occurred outside the zone of inundation, indicating that the pulse flow likely enhanced groundwater conditions in those areas as well

Summary

Introduction

In 2012, Minute 319 to the 1944 Treaty was signed (https:// www.ibwc.gov/Treaties_Minutes/Minutes.html, last access: 6 September 2018) allowing for a pulse flow of water into the Colorado River’s delta, in Mexico. During the spring of 2014 (23 March to 18 May), 130 million m3 of water were released from the United States’ Morelos Dam on the lower Colorado River to Mexico, allowing water to reach the Gulf of California for the first time in 13 years. Water is a primary environmental driver of plant productivity in our region and an important metric of the efficiency of water use is evapotranspiration (ET). Measuring plant water use or landscape-level ET is important primarily because water retention and efficient utilization is critical for the survival of humans, croplands, and natural areas. The preservation of natural areas protects water resources and the plants and animals that use those areas as habitat (Hinojosa-Huerta et al, 2013)

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