Regional climate modeling in the Amazon basin to evaluate fire risk

ABSTRACT Studies regarding deforestation, the hydrological cycle, climate change and fire weather can benefit from the detailed simulations provided by regional climate models (RCM). While much attention has been given to fire activity in the Amazon, few studies have used RCM runs to assess fire risk and variables associated to fire occurrence. We evaluated precipitation, temperature and a fire risk index from the ensemble of Eta model simulations coupled with three different global climate models for the Amazon basin. The RCM runs were compared to reanalysis data for the dry season from 1979 to 2005. The maximum and 2-m temperature fields were underestimated over the entire region, but showed a statistically significant spatial correlation with the reference data. Precipitation was overestimated over the Amazon, in accordance with the major sources of moisture analyzed. The Keetch-Byram drought index (KBDI) was not significantly affected by the bias found in temperature and precipitation, and the ensemble improved relative to the individual member simulations. KBDI estimations performed better with the ensemble of the three evaluated members, however the Eta model showed some limitations. The validation of modeled fire risk could benefit from the use of satellite hotspot data. Furthermore, the KBDI can also be used in the assessment of how climate change interacts with fire activity in the Amazon region.摘要：有关森林砍伐、水文循环、气候变化及火灾气象的研究，可借助区域气候模式（Regional Climate Model, RCM）提供的精细化模拟成果获得支撑。尽管学界已对亚马孙地区的火灾活动投入大量研究精力，但鲜有研究利用区域气候模式模拟结果评估火灾风险及与火灾发生相关的各类变量。本研究针对亚马孙流域，对耦合三种不同全球气候模式（Global Climate Model, GCM）的Eta模式（Eta model）集合模拟结果中的降水、气温及火灾风险指数开展了评估。将区域气候模式模拟结果与1979年至2005年旱季的再分析资料对比后发现：整个研究区域内的最高气温与2米气温场均被低估，但与参考数据之间存在统计学意义上显著的空间相关性；亚马孙地区的降水总量被高估，这与本次研究所分析的主要水汽来源特征相契合。基奇-拜拉姆干旱指数（Keetch-Byram Drought Index, KBDI）并未受到气温与降水偏差的显著影响，且集合模拟的整体效果优于单个成员模拟。相较于三个评估成员的单独模拟，三者的集合模拟在KBDI估算方面表现更优，但Eta模式仍存在一定局限性。针对模拟火灾风险的验证工作，可通过引入卫星热点数据得到进一步优化。此外，KBDI还可用于评估气候变化与亚马孙地区火灾活动之间的相互作用。