Multi-scale remote sensing of extreme drought impacts on vegetation productivity across drylands of the southwestern US
Abstract
Global climate warming has led to an increase in the intensity and frequency of extreme drought events with major implications for ecosystem structure and function. Yet, our knowledge of the sensitivity of ecosystem productivity, i.e., gross primary productivity (GPP), to drought extremes remains limited. This knowledge gap is especially large across highly spatial and temporal variability drylands, which are under-represented by long-term, continuous field measurements. During summer and autumn 2020, the US Southwest experienced a widespread extreme drought event, with record-low precipitation and record-high temperature across much of the region. Here, we use this event as a natural experiment to evaluate the relationship between GPP estimates and multiple remote sensing based GPP proxies across spatial scales from plot to region. First, we evaluate high frequency temporal observations from proximal remote sensing instruments including solar-induced chlorophyll fluorescence (SIF), photochemical reflectivity index (PRI), and near infrared reflectance (NIRv) measured in a wet year (2019) and an extreme drought year (2020) at the semi-arid Kendall grassland eddy covariance flux tower site (US-WKG). Next, we evaluate satellite based GPP proxies across a representative synthesis of Southwest flux tower sites and for the full Southwest region. At the site level, we found that tower-based SIF most accurately capture seasonal transitions in GPP dynamics during both the wet and extreme dry year. At the regional level, we found that SIF and NIRv were the best performing satellite GPP proxies and captured complementary aspects of seasonal GPP dynamics across dryland ecosystem types. Using a novel combination of satellite proxies, we estimate that the 2020 US Southwest drought results in a 140 Tg C (~27%) reduction in GPP, by far the lowest regional GPP over the evaluated satellite record. We finally present evidence that satellite SIF offers improved ability to track seasonal GPP dynamics across drylands by capturing near instantaneous changes in ecosystem state and physiological function from diurnal to seasonal timescales.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.B16A..04S