Field-scale assessment of land and water use change over the California Delta using remote sensing

Authors: Anderson, Martha; Gao, Feng; Knipper, Kyle; HAIN, C. - National Aeronautics And Space Administration (NASA); Dulaney, Wayne; BALDOCCHI, D. - University Of California; EICHELMANN, E. - University Of California; HEMES, K. - University Of California; Yang, Yun; MEDELLIN, AZUARA - Collaborator; Kustas, William - Bill

Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2018
Publication Date: 6/6/2018
Citation: Anderson, M.C., Gao, F.N., Knipper, K.R., Hain, C., Dulaney, W.P., Baldocchi, D., Eichelmann, E., Hemes, K., Yang, Y., Medellin, A., Kustas, W.P. 2018. Field-scale assessment of land and water use change over the California Delta using remote sensing. Remote Sensing. 10(6):889. https://doi.org/10.3390/rs10060889.
DOI: https://doi.org/10.3390/rs10060889

Interpretive Summary: Across the United States and globally there are ever increasing and competing demands for freshwater resources for use in agriculture, ecosystem support, industry and urban development. To facilitate wise water management, and to develop sustainable agricultural systems that will feed the Earth’s growing population into the future, there is a critical need for robust assessments of consumptive water use, or evapotranspiration (ET), at the scale of human management. Furthermore, we must better understand how changes in land use and land management relate to changes in water use and supply, including surface and groundwater resources. This paper investigates the performance of a multi-sensor remote sensing approach to mapping ET at sub-field spatial scales and daily timesteps. The methods are applied over the Sacramento-San Joaquin Delta region in California – an area where water resources are becoming increasingly limited due to extended drought and competitive use. The modeling system is used to estimate daily ET over the 2015 and 2016 water years, and is evaluated in comparison with ground-based measurements indicating accuracies of 1 mm/d. Annual water use patterns are then compared between different landcover and crop types, and used to quantify changes in water use that accompany specific changes in land use. The remote sensing data fusion techniques employed in this study are a cost-effective way of estimating consumptive water use in the Delta using a non-invasive, objective approach. Future work is aimed at operationalizing data production for real-time dissemination to growers and decision makers.

Technical Abstract: The ability to accurately monitor and anticipate changes in consumptive water use associated with changing land-use and land-management is critical to developing sustainable water management strategies in water-limited climatic regions. In this paper, we present an application of a remote sensing data fusion technique for developing high spatiotemporal resolution maps of evapotranspiration (ET) at scales that can be associated with changes in land use. The fusion approach combines ET map timeseries developed using an multi-scale energy balance algorithm applied to thermal data from Earth observation platforms with high spatial but low temporal resolution (e.g.,Landsat) and with moderate resolution but frequent temporal coverage (e.g., the Moderate Resolution Imaging Spectroradiometer, MODIS). The approach is applied over the Sacramento-San Joaquin Delta region in California – an area critical to both agricultural production and drinking water supply within the state that has recently experienced stresses on water resources due to a multi-year extreme drought. This landscape also presents a case study in spatiotemporal heterogeneity, representing a wide variety of irrigated and rainfed crops and natural landcovers with varying phenologies and cover fractions. ET “datacubes” with 30-m resolution and daily timesteps were constructed for the 2015-2016 water years and related to detailed maps of land-use developed at the same spatial scale. The ET retrievals are evaluated at flux sites over multiple land covers to establish a metric of accuracy in the annual water use estimates, yielding root-mean-square errors of 1.0, 0.8 and 0.3 mm d-1 at daily, monthly and yearly timesteps, respectively. Annual ET averaged over the Delta changed only 3 mm yr-1 between water years, from 822 to 819 mm yr-1, translating to an area-integrated total change in consumptive water use of 7 thousand acre-feet (TAF). Changes were largest in areas with recorded land-use change between water years - most significantly, fallowing of crop land presumably in response to reductions in water availability and allocation due to the drought. Moreover, the time evolution in water use associated with wetland restoration – an effort aimed at reducing subsidence and carbon emissions within the inner Delta – is assessed using a sample wetland chronosequence. Region-specific matrices of consumptive water use associated with land use changes could be an effective tool for policymakers and farmers to understand how land use conversion could impact consumptive use and demand.