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.
Highlights
Drought-induced reduction of vegetation production threatens both the global ecological balance and food security
A recovery of solar-induced chlorophyll fluorescence (SIF) and gross primary production (GPP) in September 2012 can be seen in for the irrigated site, Ne-1 (Figure 8c), we found no significant anomalies in the pattern of GPP, there was an obvious reduction of SIF in July and August
Ji and Peters [6] found that the most significant correlation between the Second, the spatiotemporal reduction map for the normalized difference vegetation index (NDVI) was more similar to standardprecipitation precipitation index (SPI)-3, especially in NDVI and SPI occurred for the SPI-3, while Figures 3–6 in this study show that SIF was more
Summary
Drought-induced reduction of vegetation production threatens both the global ecological balance and food security. Despite the improved performance of other VIs (e.g., NDWI, VCI, and SCDI) in monitoring drought, these reflectance-based indices fail to indicate rapid changes in drought stress because they have no direct link to photosynthetic functioning beyond their sensitivity to canopy structure and pigment concentration changes [17]. As with the LUE, SIFyield is sensitive to environmental stresses, such as water or heat stress [28,29], so SIF is expected to respond rapidly to agricultural drought and to directly indicate drought-induced reductions of vegetation production. Our objective in this study was to investigate satellite-measured SIF responses to drought by analyzing the relationship between various meteorological drought indices and SIF, and to examine whether SIF is more sensitive to short-term drought conditions than are reflectance-based VIs. Our study examined the feasibility of directly using satellite-measured SIF to monitor and assess drought. We compared drought patterns derived from meteorological drought indices, SIF, and the NDVI, and discuss our results below
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