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Recently developed solar‐induced chlorophyll fluorescence‐related vegetation indices (e.g., near infrared reflectance of vegetation (NIRv) and kernel normalized difference vegetation index (kNDVI)) have been reported to be appropriate proxies for vegetation photosynthesis. These vegetation indices can be used to estimate gross primary productivity (GPP) without considering meteorological constraints. However, it is not clear whether such a statement holds true under various environmental conditions. In this study, we explored whether these vegetation indices require meteorological constraints to better characterize GPP under extreme drought conditions using three extreme drought cases in Europe in 2003, 2010, and 2018. According to the long‐term series of observations, vegetation indices (NIRv and kNDVI) alone explained 60% and 57%, respectively, of the weekly GPP variation across the 66 flux sites. The explained variation increased to 69% and 64%, respectively, for the models that take into account radiative effects (NIRv and kNDVI multiplied by radiation). However, without considering meteorological constraints, these vegetation index‐based estimations severely underestimated negative GPP anomalies under drought stress, especially in models that incorporate radiative effects. After incorporating vapor pressure deficit (VPD)‐based meteorological constraints, the GPP estimations exhibited more pronounced negative anomalies during drought periods while maintaining model accuracy (at 70% and 65%, respectively). In addition, the GPP models based on site observations were applied at the regional scale (Europe). Our results indicated that the models without meteorological constraints again underestimated the impact of drought on GPP. This study emphasizes the importance of meteorological constraints in the estimation of GPP, especially under extreme drought conditions. Plain Language Summary: The modeling of photosynthesis usually requires temperature and moisture constraints. However, the recently developed vegetation index has been reported to be a viable alternative for estimating gross primary productivity (GPP) without the need to account for these constraints; this concept warrants further investigation. Although the vegetation index can partially capture the response of vegetation to climate change, it is insufficient for estimating GPP. This is particularly the case under extreme drought conditions, and the variation in GPP is directly affected by meteorological constraints. In this study, we used drought events in Europe during 2003, 2010, and 2018 as case studies to investigate whether the incorporation of meteorological constraints is necessary for GPP estimation using these vegetation indices. Through site observation and regional estimation, we confirmed that vegetation index‐based models without meteorological constraints tend to underestimate the impact of drought on GPP. These findings provide a significant complement to the investigation of the relationship between remotely sensed vegetation indices and photosynthesis. Key Points: Vegetation index‐based models have high uncertainty in terms of model performance and response to extreme droughtModels considering only radiation and vegetation indices underestimate the impact of extreme drought on gross primary productivityIncorporating meteorological constraints improves estimates of gross primary productivity under extreme drought conditions [ABSTRACT FROM AUTHOR]

Fire weather compounded by extremely hot and dry conditions often severely impacts society and ecosystems. To mitigate and better adapt to these compound fire weather (CFW) events, a better understanding of recent and future CFW trends is needed. Here we show that in the period 1981–2020, the global average frequency and intensity of CFW events increased by 0.6 days/yr and 0.4%/yr, respectively. Increases in temperature and decreases in relative humidity were responsible for significant trends in the frequency of CFW events in 81.7% and 58.6% of locations, respectively. The same trends contributed to significant increases in CFW intensity in 72.1% and 57.9% of locations. We further demonstrate that anthropogenic climate change (due primarily to greenhouse gas emissions) has aggravated the frequency and intensity of CFW events, particularly in the Amazon region, with over 2‐fold and 1.3‐fold increases, respectively. Future projections reveal that other (individual) fire weather events are likely to shift toward CFW events accompanied by hot‐dry conditions, along with an expected rise in CFW intensity. Furthermore, the increased occurrence of CFW events is likely to substantially augment future population exposure to CFW conditions. Under the SSP5‐8.5 scenario, climate change is estimated to contribute 62.6% of the projected increase in population exposure to CFW events by the end of this century. Our findings underscore the urgent need for strong climate action to reduce population exposure to the growing threat of future fire weather events compounded with hot and dry conditions. Plain Language Summary: In recent years, the combined impact of wildfires, heatwaves, and droughts has inflicted significant global damage. However, existing wildfire risk assessments often neglect the specific hazards arising from the co‐occurrence of heatwaves and drought, which exacerbate the consequences of wildfires. To bridge this research gap, we systematically quantified the historical changes, meteorological drivers, and future projections of compound fire weather risk (CFW) resulting from the combination of heatwaves and drought. Our findings reveal accelerated increases in the occurrence of CFW events compared with other fire weather (OFW) events, with a rise of 0.6 days per year in frequency and 0.4% per year in intensity. The predominant climatic factors driving the trend of CFW events are changes in temperature and relative humidity. Furthermore, anthropogenic climate change has further intensified the frequency and intensity of CFW events. Projections indicate a substantial rise in fire weather risk associated with heatwaves and drought throughout the 21st century, while OFW risks (such as individual fire weather events) are expected to decline. This escalation in CFW events poses a grave threat of increased population exposure, particularly under high‐emission scenarios. Key Points: The risk of fire weather events combined with hot‐dry conditions increased faster than other fire weather (OFW) events from 1981 to 2020Temperature and relative humidity play a prominent role in the trends of compound fire weather (CFW) eventsFuture projections indicate a shift from OFW events to CFW events combined with hot‐dry conditions [ABSTRACT FROM AUTHOR]

Understanding the mechanisms controlling downstream water‐level variations after the operation of the Three Gorges Dam is important for riverine flood and drought management. However, our quantitative understanding of the multiple controls of river morphology, vegetation, and floodplain resistance on water levels in the Middle Yangtze River (MYR) remains limited. Here, we analyze changes in river channels and floodplain resistance in the MYR using 450 cross‐sectional profiles as well as data on discharge, water levels, sediment, and satellite images from 2003 to 2015. Results show an overall decline in low‐flow water‐levels (at a given small discharge) due to severe incisions of low‐flow channels caused by a sharp reduction of ∼90% in sediment loads from 1950–2002 to 2003–2020. In contrast, high‐flow water‐levels (at a given large discharge) display minor changes. Our analysis shows that the notably increased floodplain resistance due to vegetation growth is likely the dominant factor elevating flood water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profiles. Our findings further the understanding of downstream geomorphic response to dam operation and their impacts on water levels and have important implications for riverine flood management in dammed river systems. Key Points: Hungry‐water‐driven channel erosion causes the sharp reduction in low‐flow water‐levelsFloodplain resistance increase dominates the minor change in high‐flow water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profileFloodplain resistance increase mainly caused by vegetation expansion in floodplain and channel bars due to the reduced floodplain submerged frequency [ABSTRACT FROM AUTHOR]