Abstract
Solar-induced chlorophyll fluorescence (SIF) from ground, airborne, and satellite-based observations has been increasingly used in drought monitoring recently due to its close relationship with photosynthesis. SIF emissions respond rapidly to droughts, relative to the widely used vegetation indices (VIs), thus indicating their potential for early drought monitoring. The response of SIF to droughts can be attributed to the confounding effects of both the physiology and canopy structure. In order to reduce the reabsorption and scattering effects, the total emitted SIF (SIFtot) was proposed and served as a better tool to estimate GPP compared with the top-of-canopy SIF (SIFtoc). However, the response time and response magnitude of SIFtot to droughts and its relationships with the environmental parameters and soil moisture (SM) (i.e., the knowledge of drought monitoring using SIFtot) remains unclear. Here, the continuous ground data of F760toc (SIFtoc at 760 nm) from a nadir view that was downscaled to F760tot (SIFtot at 760 nm), NIRv, and the NDVI, SM, meteorological, and crop growth parameters were measured from four winter wheat plots with different intensities of drought (well-watered, moderate drought, severe drought, and extreme drought) over 2 months. The results indicated that F760tot was more closely correlated with the SM than the VIs at short time lags but weaker at longer time lags. The daily mean values of F760tot and NIRv were able to distinguish the differences between different drought levels, and F760tot responded quickly to the onset of drought, especially for the moderate drought intensity. These findings demonstrated that F760tot has potential for early drought monitoring and may contribute to mitigating the risk of agricultural drought.
Highlights
Differences of F760tot, F760toc, and vegetation indices (VIs) in Responding to Different Drought Levels In Section 2.1, a dataset containing different types of measurements was obtained for subsequent analysis
The results indicated that different drought indices have specific performance for drought monitoring in different land use types in China, and this research provided an effective way to explore the potential of different drought indices for monitoring droughts
F760tot was capable of distinguishing the differences in different drought levels and responded quickly to the onset of moderate droughts compared with other variables, which appeared to have the greatest decrease; compared with F760toc, F760tot appeared to be more related to the physiology and was subjected to the canopy structure less, but these relationships varied in extreme droughts; and
Summary
Droughts are one of the most extreme and least understood climatic events in many regions of the world that has been responsible for significant socioeconomic and ecological consequences [1]. Climate change increases the global frequency and severity of droughts, exacerbating yield uncertainty and posing several risks to agriculture [2]. There is an urgent need for obtaining a better understanding of drought detection. Drought monitoring approaches have evolved from in situ station-based measurements (e.g., the Palmer Drought Severity Index (PDSI)) toward the continuous observations and monitoring of key drought-related variables at regional and global scales
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