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Increases in Compound Drought and Hot Event in the Southwestern Tibetan Plateau and Its Link to Land-Atmosphere Interactions
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DOI：10.1002/joc.70502.png)
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Abstract
En 中文
Compound drought and heatwave event (CDHE) exerts profound impacts on high-elevation areas, garnering increasing attention from the scientific community and relevant stakeholders. However, the physical mechanisms of CDHE involving land-atmosphere interaction are not fully understood in high-elevation areas. This study firstly analyzes the variations in CDHE frequency (CDHEF) over the Tibetan Plateau (TP) during the warm season (May–September) from 1980 to 2018. High-frequency CDHE occurs in the southwestern TP, where a significant increasing trend in CDHEF—exceeding 0.5 days per year—has been identified. Due to the semi-arid and semi-humid characteristics in the southwestern TP, we mainly investigate how the land-atmosphere interactions affect the interannual variations of CDHEF over this region. After removing the trend, a strong negative correlation (−0.34) is observed between soil moisture (SM) deficit and CDHEF. During years of persistent SM deficit, near-surface conditions are characterised by positive geopotential height anomalies and negative specific humidity anomalies. Meanwhile, divergence in the lower atmosphere and convergence in the upper atmosphere are observed, accompanied by subsidence throughout the entire atmospheric column over the southwestern TP. These processes work together to create favourable conditions for CDHEs. Furthermore, land-atmosphere interactions are amplified under relatively dry conditions. Reduced SM limits evapotranspiration—particularly ground evaporation and transpiration—which enhances sensible heating and elevates near-surface air temperatures. Concurrently, the lifting condensation level (LCL) grows deeper than the planetary boundary layer (PBL) height, resulting in a positive LCL deficit that further suppresses rainfall formation. The SM-evapotranspiration partitioning relationship reveals that the southwestern TP intends to shift from an energy-limited to a moisture-limited regime during dry years. Particularly, the persistent SM deficit is the potential forcing for the intensification of CDHE based on the analyses of antecedent SM-latent heat flux relationship. These findings highlight a positive feedback mechanism in which land-atmosphere interactions significantly amplify the CDHEF in southwestern TP.
Keywords:
compound drought and heatwave event
frequency
land-atmosphere interaction
soil moisture
Tibetan plateau
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