Monitoring and Assessing the 2012 Drought in the Great Plains: Analyzing Satellite-Retrieved Solar-Induced Chlorophyll Fluorescence, Drought Indices, and Gross Primary Production

Abstract

Abstract:We examined the relationship between satellite measurements of solar-induced chlorophyll fluorescence (SIF) and several meteorological drought indices, including the multi-time-scale standard precipitation index (SPI) and the Palmer drought severity index (PDSI), to evaluate the potential of using SIF to monitor and assess drought. We found significant positive relationships between SIF and drought indices during the growing season (from June to September). SIF was found to be more sensitive to short-term SPIs (one or two months) and less sensitive to long-term SPI (three months) than were the normalized difference vegetation index (NDVI) or the normalized difference water index (NDWI). Significant correlations were found between SIF and PDSI during the growing season for the Great Plains. We found good consistency between SIF and flux-estimated gross primary production (GPP) for the years studied, and synchronous declines of SIF and GPP in an extreme drought year (2012). We used SIF to monitor and assess the drought that occurred in the Great Plains during the summer of 2012, and found that although a meteorological drought was experienced throughout the Great Plains from June to September, the western area experienced more agricultural drought than the eastern area. Meanwhile, SIF declined more significantly than NDVI during the peak growing season. Yet for senescence, during which time the reduction of NDVI still went on, the reduction of SIF was eased. Our work provides an alternative to traditional reflectance-based vegetation or drought indices for monitoring and assessing agricultural drought.

The Sensitivity of Satellite Solar‐Induced Chlorophyll Fluorescence to Meteorological Drought

“…In recent years, researchers began to explore the impacts of drought on the ground‐observed SIF at local scales and satellite SIF at the regional scales. The results implied that SIF may have the potential to monitor the drought impacts on vegetation dynamics (Sun et al, ; Wang et al, ; Yoshida et al, ). Research indicated that SIF anomaly, which is the departure of SIF from the corresponding multiyear mean monthly value, could reasonably capture the spatial and temporal dynamics of drought severity (Sun et al, ).…”

Improving Estimates of Gross Primary Productivity by Assimilating Solar‐Induced Fluorescence Satellite Retrievals in a Terrestrial Biosphere Model Using a Process‐Based SIF Model

“…Chlorophyll fluorescence originates in the chloroplasts inside the leaf. It is strongly linked to CO 2 fixation (Meroni et al, ; Porcar‐Castell et al, ) and is affected by regulation mechanisms modulating photosynthesis due to environmental conditions, for example, water availability (Flexas et al, ; Sun et al, ; Wang et al, ). The top of canopy SIF emission can be expressed as the product of the absorbed photosynthetically active radiation (APAR) by the fluorescence yield of the canopy Φ F (also referred as the SIF light‐use efficiency (Guanter et al, ) that accounts for these mechanisms occurring inside the leaves) modulated by the probability Ω c that a SIF photon emitted within the canopy escapes to space (Frankenberg & Berry, ): SIF = APAR × Φ F × Ω c .…”

Using remotely sensed spectral reflectance to indicate leaf photosynthetic efficiency derived from active fluorescence measurements

“…F v ∕F m indicates the intrinsic efficiency of PSII photochemistry, which is more sensitive to environmental stress. 32 Under conditions of water stress, F v ∕F m declines as the PSII reaction center is damaged in the leaf. 59 However, chlorophyll content does not 62 and chloroplast avoidance movements.…”

“…31 Indices can still remain high when plants are heavily stressed by short-term drought while fluorescence may change dramatically. 32 It is observed that vegetation chlorophyll content is not directly linked to instantaneous photosynthetic processes and cannot quantify the downregulation of photosynthesis due to early environmental stresses. 7 The lag for the vegetation chlorophyll to response to short-term stress can cause significant uncertainties for ChlF estimates when using empirical algorithms developed by chlorophyll-related VIs, which have not been adequately elaborated and addressed.…”