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| Home > Publications database > Tracing changes in subsurface water storage through a novel satellite-based time-series of far-red solar-induced fluorescence quantum efficiency |
| Journal Article | FZJ-2026-02535 |
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2026
Elsevier Science
Amsterdam [u.a.]
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Please use a persistent id in citations: doi:10.1016/j.rse.2026.115456 doi:10.34734/FZJ-2026-02535
Abstract: Passive optical satellite products have long been used to trace drought effects. Effective mitigation and understandingland–atmosphere interactions require variables reflecting plant physiological status under water scarcity.One such variable is Solar-Induced Chlorophyll Fluorescence (SIF), emitted directly from the photosyntheticapparatus. It provides direct information on vegetation functioning and can reveal stress within days. SpaceborneSIF observations have been available for over a decade and have been widely applied for vegetation stressdetection. However, robust daily drought monitoring remains challenging because top-of-canopy SIF is stronglymodulated by canopy structure and illumination, and retrieval noise can obscure short-term drought responses.This motivates normalization approaches that better isolate the physiological component of the fluorescencesignal for near-real-time drought monitoring. To address this limitation, we estimated leaf-level fluorescencequantum efficiency (ΦF) by integrating TROPOMI SIF with photosynthetically active radiation (PAR) from theBreathing Earth Simulator (BESS), generating a daily 0.05◦ dataset for Germany (2018–2023). We evaluated ΦFas an early drought indicator in agricultural and forest ecosystems by comparing it with a subsurface waterstorage anomaly (SSWS) product from the coupled ParFlow/CLM model. Drought periods were identified asprolonged negative SSWS anomalies. Daily ΦF was aggregated, smoothed with a two-day rolling average, andanalyzed via lagged cross-correlation with surrogate-based significance testing. ΦF consistently tracked negativeSSWS anomalies with a two-day lag. This pattern was consistent across across the two analyzed land-coverclasses, indicating that ΦF detects emerging reductions in subsurface water storage with a short delay. MODISland surface temperature (LST) exhibited a complementary inverse response, peaking at 1–2 days underscoringthat the correlation found was in fact linked to water availability. In contrast, TOC SIF and common vegetationindices (NIRv, NDVI) showed weak or inconsistent correlations. These results demonstrate that ΦF enables nearreal-time detection of vegetation water stress and outperforms traditional optical indices for this purpose. Thestudy highlights the need for downscaling and normalization to transform canopy SIF observations into aneffective signal for early drought detection.
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