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Mapping Wheat Heat Stress using Sun-Induced Chlorophyll Fluorescence Measured by Satellites

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Satellite-measured sun‐induced chlorophyll fluorescence showed a potential to detect heat stress conditions in wheat and assess their impacts on wheat yields at large scales.
(a) Spatial distributions of normalized SIF, NDVI and EVI anomalies compared to the multiyear mean value during 2007–2014.(b) Monthly time series of the percentage of the wheat loss that was induced by heat stress, as indicated by SIF, NDVI, and EVI undermoderate (
Figure 5. (a) Spatial distributions of normalized SIF, NDVI and EVI anomalies compared to the multiyear mean value during 2007–2014. (b) Monthly time series of the percentage of the wheat loss that was induced by heat stress, as indicated by SIF, NDVI, and EVI during 2007–2014

Liangzhi You from IFPRI co-authored a paper recently published in Global Change Biology, where the authors examined the potential of using the satellite-measured sun‐induced chlorophyll fluorescence, along with the traditional vegetation indices, to monitor the heat stress of winter wheat at scale across the Indo-Gangetic Plains area.

Abstract
Extremely high temperatures represent one of the most severe abiotic stresses limiting crop productivity. However, understanding crop responses to heat stress are still limited considering the increases in both the frequency and severity of heat wave events under climate change. This limited understanding is partly due to the lack of studies or tools for the timely and accurate monitoring of crop responses to extreme heat over broad spatial scales. In this work, we use novel spaceborne data of sun‐induced chlorophyll fluorescence (SIF), which is a new proxy for photosynthetic activity, along with traditional vegetation indices (Normalized Difference Vegetation Index NDVI and Enhanced Vegetation Index EVI) to investigate the impacts of heat stress on winter wheat in northwestern India, one of the world’s major wheat production areas. In 2010, an abrupt rise in temperature that began in March adversely affected the productivity of wheat and caused yield losses of 6% compared to the previous year. The yield predicted by satellite observations of SIF decreased by approximately 13.9%, compared to the 1.2% and 0.4% changes in NDVI and EVI, respectively. During the early stage of this heat wave event in early March 2010, the SIF observations showed a significant reduction and earlier response, while NDVI and EVI showed no changes and could not capture the heat stress until late March. The spatial patterns of SIF anomalies closely tracked the temporal evolution of the heat stress over the study area. Furthermore, our results show that SIF can provide large‐scale, physiology‐related wheat stress response as indicated by the larger reduction in fluorescence yield (SIFyield) than a fraction of photosynthetically active radiation during the grain‐filling phase, which may have eventually led to the reduction in wheat yield in 2010. This study implies that satellite observations of SIF have great potential to detect heat stress conditions in wheat in a timely manner and assess their impacts on wheat yields at large scales.

Song, L., Guanter, L., Guan, K., You, L., Huete, A., Ju, W., & Zhang, Y. (2018). Satellite sun‐induced chlorophyll fluorescence detects early response of winter wheat to heat stress in the Indian Indo‐Gangetic Plains. Global change biology. https://doi.org/10.1111/gcb.14302