Comparison of Actual Evapotranspiration Estimates Using Two Methods of Vegetation-Indexed and Energy-Balanced Over Riparian Zones: A Case Study of Colorado River Delta
Neda Abbasi1,2*, Hamideh Nouri3, Pamela Nagler4*, Sattar Chavoshi Borujeni5,6, Kamel Didan7, Armando Barreto Munoz8, Christian Opp9, Ibrahima Sall10, Gabriel Senay11, Stefan Siebert12
1 Department of Crop Sciences, University of Göttingen, Von-Siebold-Straße 8, 37075, Göttingen, Germany; neda.abbasi@agr.uni-goettingen.de
2Department of Geography, Philipps-Universitat Marburg, Deutschhausstrafe 10, 3502, Marburg, Germany; neda.abbasi@agr.uni-goettingen.de
3 Department of Crop Sciences, University of Göttingen, Von-Siebold-Straße 8, 37075, Göttingen, Germany; hamideh.nouri@uni-goettingen.de
4 U.S. Geological Survey, Southwest Biological Science Center, 520 N. Park Avenue, Tucson, AZ 85719, USA; pnagler@usgs.gov
5 School of Environment, University of Technology Sydney, Ultimo, NSW 2007, Australia; Sattar.Chavoshiborujeni@student.uts.edu.au
6 Soil Conservation and Watershed Management Research Department, Isfahan Agricultural and Natural Resources Research and Education Centre, AREEO, Isfahan, Iran; Sattar.Chavoshiborujeni@student.uts.edu.au
7 Biosystems Engineering. The University of Arizona, 1177 E. 4th St., Tucson, AZ 85719, USA; didan@arizona.edu
8 Biosystems Engineering. The University of Arizona, 1177 E. 4th St., Tucson, AZ 85719, USA; abarreto@arizona.edu
9 Department of Geography, Philipps-Universitat Marburg, Deutschhausstrafe 10, 3502, Marburg, Germany; opp@mailer.uni-marburg.de
10 Agricultural and Resource Economics. The University of Arizona, 1177 E. 4th St., Tucson, AZ 85719, USA; isall@arizona.edu
11 US Geological Survey (USGS) Earth Resources Observation and Science Center, North Central Climate Adaptation Science Center, Fort Collins, CO 80523, USA; senay@usgs.gov
12 Department of Crop Sciences, University of Göttingen, Von-Siebold-Straße 8, 37075, Göttingen, Germany; stefan.siebert@uni-goettingen.de
Understanding the water consumption and vegetation dynamics in riparian zones is important to develop and maintain sustainable water management plans for the riparian ecosystems. This study focuses on estimating consumptive water use of a riparian corridor located in the Colorado River delta, characterized by distinctive hydrology conditions and strongly influenced by the watercourse. Apart from the climatological characteristics of the region, a challenging problem that arises in this domain is the need for accurate and spatially explicit water consumption data for drought monitoring and a long-term record of riparian water use. In this research, we compared two Remote Sensing-based (RS) actual evapotranspiration (ETa) estimates as a tool to map and monitor riparian zones’ water consumption (2003-2019). RS-based ET approaches provide spatial estimates that can be frequently updated and used across areas where ground measurements are scarce. The Vegetation-Index (VI) -based ETa (ET-VI). ET-VI method uses mainly optical and near-infrared bands to calculate VIs and combine them with reference ET to estimate ETa. In this study, 2-band Enhanced Vegetation Index (EVI2) was calculated using Landsat imagery (with a spatial resolution of 30 meters) to derive ETa. All calculations were conducted on an open-access platform, Google Earth Engine, for geospatial analysis with computational capabilities and direct access to RS data. The second method is the Operationalized Simplified Surface Energy Balance ETa product, (SSEBOp-ETa, spatial resolution: 1 kilometer) which is an open-access product and uses RS-based thermal data from MODIS sensor and assimilated weather data to predict ETa. The time series analysis of both ETa estimates revealed that the riparian ecosystem has been experiencing loss in its corresponding water resources, especially within the last decade due to drought and water scarcity. The ETa trend assessment showed a significant decrease in ET-EVI2 about 4 (mm/year) and a non-significant decrease in SSEBOp-ETa (8 mm/year). The findings of our study emphasize the potential of RS-based ETa as an effective tool for fast hydrological monitoring, riparian zones management, and climate change studies. We encourage inter-comparison of RS-based methods with other empirical methods and the use of high-resolution sensors in the ETa derivation to monitor drought, riparian vegetation health, and water consumption.