Warm Early Summer Compensated Reduction in Photosynthesis Caused by 2022 Late Summer Extreme Drought Over the Tibetan Plateau

The Tibetan Plateau (TP) is ecologically delicate, its vegetation highly sensitive to climate variations. In 2022, China endured an unprecedented compound drought-heatwave, escalating TP's August temperature to a record high since 2000. This study examined this event's impact on TP's photosynthesis using multi-source satellite-based products. We demonstrated persistent high temperatures from April to August 2022, accompanied by shifting soil water (SW). Initially moist from April to June, the soil turned notably dry, hitting its lowest point in August. Consequently, early summer witnessed a substantial enhancement in gross primary productivity (GPP) and near-infrared reflectance of vegetation (NIRv) predominantly due to high temperatures, except for reduction in the eastern and southeastern TP. June recorded the largest positive GPP anomaly since 2000. As summer progressed, severe drought, not high temperatures, dominated, causing obvious negative anomalies in GPP and NIRv, especially in August, concentrated in the central and southwestern TP. Separating the growing season into May-June-July (MJJ) and August-September (AS) revealed a clear contrast. Enhancement in photosynthesis during MJJ compensated the decline in AS, making average positive GPP and weak negative NIRv anomalies in the entire growing season. Specifically, MJJ saw GPP magnitudes of 5.724 TgC mo-1 in FluxSat, 9.491 TgC mo-1 in GPP v2.2 and OCO-2-based Solar-induced chlorophyll fluorescence (GOSIF), and 0.004 in NIRv. Conversely, AS experienced a decline: -4.802 TgC mo-1 in FluxSat, -2.837 TgC mo-1 in GOSIF GPP, and -0.006 in NIRv. This delicate balance underscores the intricate interplay between early growth conditions, subsequent environmental stressors, and vegetation's adaptive responses. In 2022, an extreme heat and dry event hit the ecologically fragile Tibetan Plateau (TP) in China. We used satellite data to analyze its impact. From April to August, the TP faced prolonged high temperatures, coupled with shifting soil water. Initially moist in April-June, the soil dried drastically, reaching its lowest in August. Early summer witnessed a substantial enhancement in vegetation photosynthesis, mainly due to high temperatures. However, as summer progressed, severe drought took hold, leading to decreased plant productivity, particularly in August, especially in the central and southwestern TP. By dividing the growing season into two periods (May-June-July [MJJ] and August-September [AS]), we found that photosynthesis during MJJ compensated for the later decline in AS, causing an overall positive GPP and a mild negative near-infrared reflectance of vegetation throughout the growing season. This study highlights the delicate balance between early growth conditions, subsequent environmental pressures, and plants' adaptive responses in the TP. Extreme heat and drought caused obvious drop in photosynthesis during August-September (AS) in 2022 in the Tibetan PlateauWarm early summer compensated reduction in photosynthesis in late summerPhotosynthesis anomaly was temperature-driven in May-June-July, shifting to soil water control in AS