The Tinderbox Drought (2017–2019) was one of the most severe droughts recorded in Australia. The extreme summer air temperatures (>40 °C) combined with drought, contributed to the unprecedented Black Summer bushfires in 2019–20 over southeast Australia. Whilst the temperature extremes were largely driven by synoptic processes, it is important to understand to what extent interactions between land and atmosphere played a role. In this study, we use the WRF-LIS-CABLE land-atmosphere coupled model to examine the impacts of changes in leaf area index (LAI) and albedo by contrasting simulations with climatological and time-varying LAI and albedo. We analyse the impact of these biophysical feedbacks on temperature extremes and fire risk during the Tinderbox Drought and the Black Summer bushfires. Remote-sensing data showed a decrease in LAI (0.1–4.0 m m) over the three years of the drought along the southeast coast of Australia relative to the long-term climatology, while albedo increased inland (0.02–0.14). These changes in LAI and albedo were accompanied by an overall decrease in daily maximum temperature (T) in the vast majority of interior regions (by ∼0.5 °C) and, in the 2019–20 summer, by a clear increase in T in the coastal regions of up to ∼1 °C. Increased albedo explained most of the decreases in T inland, whereas increases in T along the coasts were mostly associated with LAI declines. The magnitude of the impact of biophysical changes on temperature demonstrates the potential impact that would be missed in simulations that assumed fixed vegetation properties. Finally, we only found a small impact from LAI and albedo changes on the fire risk (as measured by the fuel moisture index) preceding the Black Summer bushfires, suggesting these biophysical feedbacks did not significantly modulate fire risk. Our results have implications for coupled simulations relying on climatological LAI and albedo, including operation weather and seasonal climate predictions.

中文翻译：

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研究生物物理反馈对澳大利亚东南部 Tinderbox 干旱和黑夏丛林大火期间模拟极端温度的作用


Tinderbox 干旱（2017-2019 年）是澳大利亚有记录以来最严重的干旱之一。夏季极端气温 (>40 °C) 加上干旱，导致 2019-20 年澳大利亚东南部发生史无前例的黑夏丛林大火。虽然极端温度很大程度上是由天气过程驱动的，但了解陆地和大气之间的相互作用在多大程度上发挥了作用非常重要。在本研究中，我们使用 WRF-LIS-CABLE 陆地-大气耦合模型，通过将模拟与气候和时变 LAI 和反照率进行对比，研究叶面积指数 (LAI) 和反照率变化的影响。我们分析了这些生物物理反馈对火药桶干旱和黑夏丛林大火期间极端温度和火灾风险的影响。遥感数据显示，在干旱的三年中，澳大利亚东南沿海地区的 LAI 相对于长期气候有所下降（0.1-4.0 毫米），而内陆反照率则有所增加（0.02-0.14）。 LAI 和反照率的这些变化伴随着绝大多数内陆地区每日最高气温 (T) 的整体下降（约 0.5 °C），并且在 2019-20 年夏季，内陆地区的 T 明显上升。沿海地区气温可达~1°C。反照率的增加解释了内陆 T 的大部分下降，而沿海 T 的增加主要与 LAI 的下降有关。生物物理变化对温度影响的大小表明了在假设固定植被特性的模拟中可能会忽略的潜在影响。 最后，我们只发现黑夏丛林大火之前的 LAI 和反照率变化对火灾风险（通过燃料湿度指数测量）产生很小的影响，这表明这些生物物理反馈并没有显着调节火灾风险。我们的结果对依赖于气候 LAI 和反照率的耦合模拟（包括运行天气和季节性气候预测）具有影响。