# Impacts of Drought and Heatwave on the Vegetation and Ecosystem in the Yangtze River Basin in 2022
## 1 Introduction  
Drought and heatwave are among the most common natural ecosystem disasters globally and are often associated with prolonged periods of abnormally low precipitation or exceptionally high temperatures lasting from several months to several years [1]. They can inflict severe damage upon terrestrial ecosystems [2], such as reducing vegetation productivity [3], thereby destroying the ecosystem carbon balance [4]. During the summer of 2022, many regions worldwide, including Europe and Asia, experienced extraordinarily high temperatures [5]. China was no exception, facing its most severe meteorological drought and heatwave event since comprehensive meteorological records began in 1961 [6]. [PERSON]'s study indicated that cities along the Yangtze River Basin witnessed daytime maximum temperatures exceeding 42 \({}^{\circ}\)C, enduring over 40 consecutive days of heatwave conditions and more than 32 days of compounded hot weather [7]. As a result of the drought, the Yangtze River Basin experienced an unprecedented shortage of precipitation [8], significantly reducing hydroelectric power generation. Consequently, Sichuan Province encountered a substantial decline in its power supply capacity, greatly impacting the lives and productivity of the local residents [9]. The response of vegetation to drought and heatwave serves as a crucial indicator for assessing the health of terrestrial ecosystems [10]. Typically, during such periods, vegetation undergoes alterations in photosynthetic activity [11], consequently leading to a decline in productivity [12]. Vegetation indices (VIs) that measure greenness, such as the Normalized Difference Vegetation Index (NDVI), have been extensively used to evaluate the influence of water and heat stress on vegetation productivity during prolonged periods of drought and heatwave [13; 14]. However, these conventional green VIs often only reflect the greenness of the vegetation canopy or chlorophyll content, solely pertaining to the potential photosynthetic activity of the vegetation, without considering the actual photosynthetic process [1; 15]. Recent research has shown a growing consensus that solar-induced chlorophyll fluorescence (SIF) is an outcome of vegetation photosynthesis and is closely associated with gross primary production (GPP) [16; 17; 18]. Consequently, many scholars argue that SIF is more sensitive to environmental stressors compared to green-based VIs [19; 20; 21]. Under the combined conditions of high temperatures and reduced rainfall, vegetation responds to the increased vapor pressure deficit (VPD) by closing stomata to reduce water dissipation [22; 23]. Consequently, soil moisture decreases, exacerbating vegetation water deficit, which further prompts plants to reduce stomatal aperture to mitigate water loss, thus adapting to the water-deficient conditions [24; 25]. This, in turn, exacerbates vegetation damage [26; 27]. Numerous academics argue that vegetation in arid regions at mid-latitudes exhibits heightened sensitivity to fluctuations in water availability [25; 28]. They suggest that the atmosphere in arid regions is already very dry and hot, hence vegetation exhibits robust resistance to the rising levels of VPD. However, there are also dissenting opinions, with some scholars proposing that high VPD may have a greater impact on vegetation growth than low soil moisture. For instance, [PERSON], in analyzing drought and heatwave in both Yunnan and southern China, suggested that the correlation between VPD and SIF yield tends to be stronger at spatiotemporal scales [1]. Furthermore, different types of vegetation ecosystems exhibit varying responses to drought and heatwave [10; 29; 30; 31]. For instance, some scholars suggest that the intensification of temperature exacerbates the degree of drought most significantly in temperate desert and grassland regions, while its effect is weakest in mixed coniferous-deciduous forest areas and cold temperate coniferous forest regions [32].