Abstract
Droughts and heatwaves in the Mediterranean can induce plant activity decline and severe wildfires leading to considerable economic, social and environmental damages. This study aims at statistically quantifying the isolated and combined impacts of these extreme events based on a combination of regional land surface-atmosphere modeling and satellite observations of surface properties (MODIS). A simulation by the RegIPSL coupled regional model (ORCHIDEE-WRF) over the 1979–2016 period in the Western Mediterranean is used to identify heatwaves and droughts. After an evaluation of the model performance against surface observations of temperature and precipitation, a spatio-temporal analysis is conducted using specific indicators of extreme events: Percentile Limit Anomalies (PLA) and the Standardized Precipitation Evapotranspiration Index (SPEI). The impact on vegetation and wildfires is assessed using the MODIS observations of Leaf Area Index (LAI), burned area (BA) and fire radiative power (FRP), clustered by simulated extreme weather events. Due to water stress, droughts lead to significant biomass decrease (− 10% LAI on average and reaching − 23% in some areas). The isolated effect of heatwaves is smaller (sim − 3% LAI) so that the combined effect is dominated by the impact of droughts. Heatwaves and droughts significantly exacerbate wildfire regimes. Through synergistic effects, simultaneous droughts and heatwaves increase BA and FRP by 2.1 and 2.9 times, respectively, compared to normal conditions. By reducing biomass, droughts slightly decrease fuel availability. However, our results show that the inter-annual variation in fire activity is mainly driven by weather conditions rather than fuel load.
Highlights
In line with what is expected in a context of global warming, droughts and heatwaves have increased both in frequency and severity over the last century in the Mediterranean area
The objective of this study is to quantify the isolated and combined impacts of heatwaves and droughts on vegetation and wildfires, using extreme events identified based on regional land surface-atmospheric modeling and impacts observed by satellite observations of surface properties (MODIS)
While simulated summer mean 2 m temperature and rainfall from Med-CORDEX show a constant daily overestimation compared to E-OBS, they are within its range of standard error
Summary
In line with what is expected in a context of global warming, droughts and heatwaves have increased both in frequency and severity over the last century in the Mediterranean area. These types of drought are manifested by, respectively, a rainfall deficit, a limited soil water reservoir for surface and underground flows, and a water shortage for plant growth (Vicente-Serrano et al 2012; Svoboda et al 2016) The occurrence of these extreme events over the Mediterranean is directly linked to weather regimes at the synoptic scale with, for instance, the Atlantic Low and the Blocking regime, which bring warm and dry air in summer over the Mediterranean Droughts in the Mediterranean can lead to heatwaves in continental Europe tempered by the northward transport of warm and dry air, with episodes of southerly winds (Vautard et al 2007) During such extreme conditions, vegetation is exposed to water and heat stresses. LAI variation from MODIS is compared to the simulated one by Med-CORDEX
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