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Abstract:
The 2018 summer heatwaves over Northern Europe and USA were unexpected extreme and complex cases combined with droughts. To investigate the compound heatwave cases and the role of land-air interaction with progress in soil water content and air temperature, ERA5 reanalysis data, CPC temperature, GLEAM, and ESA-CCI datasets are examined. Also, Global Seasonal Forecasting System is used to validate predictive performance in summer 2018. Based on observational and reanalysis datasets, the model performance of the water-limited regime and energy-limited regime is spatially verified over Northern Europe and USA. A combination of drought and heatwave occurred, and the breakpoint, which is the basis for the phase in which land-atmosphere feedback is placed in positive and as the threshold value of soil water content that daily maximum temperature becoming more sensitive with soil water declining, is established at each grid points for both forecasting model, observational and reanalysis data. When the dry side of the soil water content is well simulated in the forecast model, the heat wave forecasting skill score is improved. Even in the coupled forecasting model, there is a regime in which the daily maximum temperature is hyper-sensitive with decreasing in soil water content and, when the soil water content is well simulated, land-air positive feedback is well expressed within dry regime. This study estimates the improvement of heatwave prediction skills by simulating soil water and daily maximum temperature relationship in hyper-sensitive regimes and land-air interaction plays an important role as sources in extreme heat events cases.
