Synergistic use of SMAP and OCO-2 data in assessing the responses of ecosystem productivity to the 2018 U.S. drought

Authors: LI, X, - University Of New Hampshire; XIAO, J. - University Of New Hampshire; KIMBALL, J.S. - University Of Montana; REICHLE, R.H. - National Aeronautics And Space Administration (NASA); Scott, Russell - Russ; LITVAK, M.E. - University Of New Mexico; BOHRER, G. - The Ohio State University; FRANKENBERG, C. - Jet Propulsion Laboratory

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2020
Publication Date: 12/15/2020
Citation: Li, X., Xiao, J., Kimball, J., Reichle, R., Scott, R.L., Litvak, M., Bohrer, G., Frankenberg, C. 2020. Synergistic use of SMAP and OCO-2 data in assessing the responses of ecosystem productivity to the 2018 U.S. drought. Remote Sensing of Environment. 251, Article 112062. https://doi.org/10.1016/j.rse.2020.112062.
DOI: https://doi.org/10.1016/j.rse.2020.112062

Interpretive Summary: There are new measurements from space satellites that can potentially help us to better monitor drought and the corresponding response of plant productivity over vast regions. Therefore, this study compared new satellite estimates of soil moisture and photosynthesis over the southwestern United States during the 2018 drought and examined to what extent they could characterize the drought-induced changes seen in land-based measurements. The results showed that the different satellite-estimates of plant productivity matched well with satellite-estimated soil dryness as well as land-based measurements of plant productivity. The combined use of different satellite estimates of plant productivity and soil moisture can adequately depict drought changes and its impact on productivity over time and across the US, helping us to better measure the impact of drought on agriculture, forests and rangelands.

Technical Abstract: Soil moisture, solar-induced chlorophyll fluorescence (SIF), and gross primary productivity (GPP) estimates from the Soil Moisture Active Passive (SMAP) and the Orbiting Carbon Observatory-2 (OCO-2) provide new opportunities for understanding the relationship between soil moisture and terrestrial photosynthesis at large scales. Here we explored the potential of SMAP and OCO-2 based data for monitoring the responses of ecosystem productivity to drought. We made use of complimentary observational information on root-zone soil moisture and GPP from SMAP, SIF from OCO-2, and finer-resolution SIF derived from downscaling of coarse-resolution OCO-2 SIF (GOSIF). We compared the spatial pattern and temporal evolution of anomalies of these variables over the southwestern United States (US) during the 2018 drought, and examined to what extent they could characterize the drought-induced variations of eddy covariance flux tower based GPP and US Department of Agriculture crop yield data. Our results showed that all three proxies of productivity (SMAP GPP, OCO-2 SIF and GOSIF) could well capture the spatial extent and dynamics of drought indicated by the SMAP root-zone soil moisture deficit. The anomalies of 8-day SMAP GPP and GOSIF also coincided with drought conditions indicated from the U.S. Drought Monitor maps. At the regional scale, soil moisture anomalies showed significant positive correlations with SMAP GPP (r=0.60-0.66, p<0.001) and GOSIF (r=0.80-0.87, p<0.001), demonstrating strong water availability constraints on plant productivity. We further found that SMAP GPP and GOSIF revealed the impact of drought on tower GPP and crop yield. Our results suggest that the combined use of SMAP and OCO-2 can adequately depict drought evolution and its impact on ecosystem productivity at multiple spatial and temporal scales, and demonstrate the value of SMAP and OCO-2 in studying ecosystem function, and carbon cycling, and climate change.