Eponymous Wildfires

The intensification of global climate change and human activities has made drought one of the most severe global challenges, bringing unprecedented challenges to the hydrological and water resource system. Although several studies have been conducted on hydrological droughts, few have examined the response relationship between hydrological droughts and water and energy balance. This study uses multi-year drought detection and the Budyko framework to investigate the impact of climate change and human activities on runoff changes, with a focus on the differences between drought and non-drought conditions. The results indicate that (1) the sensitivity of runoff to precipitation (εPR), potential evapotranspiration (PET) (εPET), and the watershed characteristic parameter n (εn) varies over time, initially increasing and then decreasing, and peaking between 1995 and 2006. Runoff is most sensitive to precipitation (PR) and least sensitive to potential evapotranspiration (PET). (2) The dominant contribution shifted from climate change during 1977–1985 to human activities during 1986–2014. (3) Multi-year drought in the Yellow River Basin (YRB) significantly altered n, εPR, εPET, and εn, changing from (1.50, 2.19, −1.19, −5.66) in non-drought periods to (1.84, 2.57, −1.57, −9.93) in drought periods, with greater absolute values during drought periods. (4) Compared to non-drought periods, the contribution scores of human activities (δh) are significantly higher. The growing contribution of human activities to runoff can exacerbate the occurrence of hydrological droughts.

Multi-year droughts (MYDs) are severe natural hazards that have become more common due to climate change. Given their significant societal impact compared to normal droughts (ND) of shorter duration, it is crucial to better understand the drivers of MYDs. In this work we used a combination of a large-ensemble of climate models and reanalysis data to study the difference between MYDs and NDs. For six different climatic regions, chosen to be of similar size to the dominating regional atmospheric circulation patterns, we used reanalysis data of precipitation and potential evapotranspiration to show the regional characteristics and drivers of MYDs and contrast these with characteristics of NDs. Our findings reveal that MYD occurrence and duration varies significantly between the regions, where relatively larger differences in duration between MYD and NDs can indicate different drivers resulting in the different drought durations. Regions with distinctive seasonality in their precipitation climatology tend to experience faster drought onsets compared to regions with climatologically steady precipitation. Furthermore, our analysis shows that MYDs and NDs often start with similar conditions but diverge over time, and that longer-term memory is present in some regions, which might provide avenues for the predictability of MYDs. However, since MYDs are rare events (2 to 6 MYDs per region between 1950-2023 in this study), we supplement reanalyis data with that of CMIP6 climate models with a large number of ensembles to assess the drivers of MYDs with more statistical rigour. This creates the opportunity to study the contributions of oceans, soil moisture, snow, and other climate variables on the persistent circulation patterns leading to MYDs, and to find the influence of climate variability on the occurrence of MYDs.DOI: http://dx.doi.org/10.2139/ssrn.4974995

Droughts' persistent impact and growing use of surface water and groundwater will likely exacerbate hydrological droughts. Variations in precipitation patterns worsen the effects in particular catchment regions as a result to climate change. The end result is less groundwater recharge and multi-year droughts that impact vegetation and rivers.An essential factor to better understand the recovery in catchments affected by drought is to understand the interaction between water availability and vegetation dynamics. At the same time, the vegetation recovery in terms of growth and productivity can also be assessed with this framework. In this study, we focus on natural catchments of central Chile which have experienced drought and multi-year drought periods with severe impacts on surface water and groundwater.We collected 250 tree ring samples of 5 species that are susceptible to droughts in central Chile in natural catchments, and used CAMELS-CL for statistical analysis. Cross correlation analysis between surface, groundwater and vegetation dynamics was performed for each catchment to quantify the interaction between these factors. To further determine the influence of drought events on vegetation, the compound NDVI correlation and SPEI at a catchment level were used. Finally, the drought termination framework was applied to understand the recovery response of surface, groundwater and vegetation.Our analysis identifies the typical time lag between droughts in surface water, groundwater and  their impact on vegetation growth. This is done on an annual time scale as we are looking at multi-year events. We find that the typical response time varies throughout the country, depending on the local natural water availability. These findings highlight that the multi-year drought impact on vegetation and its recovery is not uniform and should be better understand in light of climate change and the global increase in multi-year drought events.

Forest fires constitute a major environmental and socioeconomic hazard in the Mediterranean. Weather and climate are among the main factors influencing forest fire potential. As fire danger is expected to increase under changing climate, seasonal forecasting of weather conditions conductive to fires is of paramount importance for implementing effective fire prevention policies. The aim of the current study is to provide high resolution (~9 km) probabilistic seasonal fire danger forecasts, utilizing the Canadian Fire Weather Index (FWI) for Attica region, one of the most fire prone regions in Greece and the Mediterranean, employing the fifth generation ECMWF seasonal forecasting system (SEAS5). Results indicate that FWI and its Initial Spread Index (ISI) sub-component, present statistically significant high discrimination scores and are proven respectively, marginally useful, and perfectly reliable in predicting above normal fire danger conditions. When comparing year-by-year the fire danger predictions with the historical fire occurrence obtained by the Hellenic Fire Service database, both seasonal FWI and ISI forecasts indicate a skill in identifying years with high fire occurrences. Overall, fire danger and its sub-components can potentially be exploited by regional authorities in fire prevention management regarding preparedness and resources allocation in the Attica region.

Abstract. Forest fires constitute a major environmental and socioeconomic hazard in the Mediterranean. Weather and climate are among the main factors influencing forest fire potential. As fire danger is expected to increase under changing climate, seasonal forecasting of meteorological conditions conductive to fires is of paramount importance for implementing effective fire prevention policies. The aim of the current study is to provide high-resolution (∼9 km) probabilistic seasonal fire danger forecasts, utilizing the Canadian Forest Fire Weather Index (FWI) for the Attica region, one of the most fire-prone regions in Greece and the Mediterranean, employing the fifth-generation ECMWF seasonal forecasting system (SEAS5). Results indicate that, depending on the lead time of the forecast, both the FWI and ISI (Initial Spread Index) present statistically significant high discrimination scores and can be considered reliable in predicting above-normal fire danger conditions. When comparing the year-by-year fire danger predictions with the historical fire occurrence recorded by the Hellenic Fire Service database, both seasonal FWI and ISI forecasts are skilful in identifying years with a high number of fire occurrences. Overall, fire danger and its subcomponents can potentially be exploited by regional authorities in fire prevention management regarding preparedness and resources allocation.

The UK is vulnerable to wildfire, and vulnerability is likely to increase due to climate change. Whilst the risk is small compared with many other countries, recent fires have raised awareness and highlighted the potential for environmental damage and loss of property and key infrastructure. Most UK wildfires are a result of inadvertent or deliberate human action, but the environmental conditions depend on antecedent and current weather. This paper presents projections of the effects of climate change on UK wildfire danger, using a version of an operational fire danger model, UKCP18 climate projections representing low and high emissions, and several indicators of fire danger. Fire danger will increase across the whole of the UK, but the extent and variability in change varies with indicator. The absolute danger now and into the future is greatest in the south and east (the average number of danger days increases 3–4 times by the 2080s), but danger increases further north from a lower base. The variation in change across the UK for indicators based on absolute thresholds is determined by how often those thresholds are exceeded now, whilst the (lesser) variability in percentile-based indicators reflects variability in the projected change in climate. Half of the increase in danger is due to increased temperature, and most of the rest is due to projected reductions in relative humidity. Uncertainty in the magnitude of the change is due to uncertainty in changes in temperature, relative humidity, and rainfall, and there is a large difference between two of the UKCP18 climate model ensembles. Reducing emissions to levels consistent with achieving international climate policy targets significantly reduces, but does not eliminate, the increase in fire danger. The results imply that greater attention needs to be given to wildfire danger in both emergency and spatial planning, and in the development of guidelines for activities that may trigger fires. They suggest the need for the development of a fire danger system more tailored to UK conditions, and the combination of fire danger modelling with projections of sources of ignition to better estimate the change in wildfire risk.

The interactions between natural water availability and societal water demand and management are complex. In response to gaps in empirical research of the adaptive capacity of social and environmental systems to climate stresses, we provide an assessment of responses to water scarcity during a multi-year drought in California. In particular, we use Barnett and O’Neill’s (Global Environ Change 20:211–213, 2010) criteria for maladaptation to examine responses in the agricultural and energy sectors to a multi-year (2007–2009) California drought. We conclude that despite evidence in both sectors of resiliency to the impacts of the drought, some of the coping strategies adopted increased the vulnerability of other systems. These other systems include California’s aquatic ecosystems and social groups that rely on those ecosystems for their health or employment; future generations whose resources were drawn down in the near-term, where otherwise those resources would have been available at a later time; and current and future generations who were, or will be, exposed to the effects of increased greenhouse gas emissions. This case study demonstrates that California’s current strategies for dealing with long or severe droughts are less successful than previously thought when short- and long-term impacts are evaluated together. This finding is particularly relevant given projections of more frequent and severe water shortages in the future due to climate change. This study recommends a shift from crisis-driven responses to the development and enactment of long-term mitigation measures that are anticipatory and focus on comprehensive risk reduction.

<p>Weather and climate play an important role in shaping global fire regimes and geographical distributions of burnable areas. At the global scale, fire danger is likely to increase in the near future due to warmer temperatures and changes in precipitation patterns, as projected by the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). There is a need to develop the most reliable projections of future climate-driven fire danger to enable decision makers and forest managers to take both targeted proactive actions and to respond to future fire events.</p><p>Climate change projections generated by Earth System Models (ESMs) provide the most important basis for understanding past, present and future changes in the climate system and its impacts. ESMs are, however, subject to systematic errors and biases, which are not fully taken into account when developing risk scenarios for wild fire activity. Projections of climate-driven fire danger have often been limited to the use of single models or the mean of multi-model ensembles, and compared to a single set of observational data (e.g. one index derived from one reanalysis).</p><p>Here, a comprehensive global evaluation of the representation of a series of fire weather indicators in the latest generation of ESMs is presented. Seven fire weather indices from the Canadian Forest Fire Weather Index System were generated using daily fields realisations simulated by 25 ESMs from the 6<sup>th</sup> Coupled Model Intercomparison Project (CMIP6). With reference to observational and reanalysis datasets, we quantify the capacity of each model to realistically simulate the variability, magnitude and spatial extent of fire danger. The highest-performing models are identified and, subsequently, the limitations of combining models based on independency and equal performance when generating fire danger projections are discussed. To conclude, recommendations are given for the development of user- and policy-driven model evaluation at spatial scales relevant for decision-making and forest management.</p>

Global warming is expected to increase droughts and heatwaves, and consequently fire danger in southern Europe in the forthcoming decades. However, an assessment of the uncertainties associated with this general trend at regional scales, relevant to decision-making, is still missing. This study aims at assessing potential climate change impacts on fire danger over France through the projection of the widely used Fire Weather Index (FWI) and at quantifying the different sources of climate-driven uncertainty associated with these projections. We used daily climate experiments covering the 1995–2098 period under two scenarios (RCP4.5 and RCP8.5) provided by the EURO-CORDEX initiative. Our results show an overall increase in FWI throughout the century, with the largest absolute increases in the Mediterranean area. Model uncertainty was very high in western France, previously identified as a potential fire-prone region under future climate. In contrast, large increases in FWI in the Mediterranean area showed low uncertainty across models. Besides, analyzing the natural variability of FWI revealed that extreme years under present-day climate could become much more frequent by the end of the century. The FWI is projected to emerge from the background of natural variability by mid-twenty-first century with a summer elevated fire danger three times more likely when summer temperature anomaly exceeds + 2 °C.

Abstract. Forest fire danger rating based on sparse meteorological stations is known to be potentially misleading when assigned to larger areas of complex topography. This case study examines several fire danger indices based on data from two meteorological stations at different elevations during a major drought period. This drought was caused by a persistent high pressure system, inducing a pronounced temperature inversion and its associated thermal belt with much warmer, dryer conditions in intermediate elevations. Thus, a massive drying of fuels, leading to higher fire danger levels, and multiple fire occurrences at mid-slope positions were contrasted by moderate fire danger especially in the valleys. The ability of fire danger indices to resolve this situation was studied based on a comparison with the actual fire danger as determined from expert observations, fire occurrences and fuel moisture measurements. The results revealed that, during temperature inversion, differences in daily cycles of meteorological parameters influence fire danger and that these are not resolved by standard meteorological stations and fire danger indices (calculated on a once-a-day basis). Additional stations in higher locations or high-resolution meteorological models combined with fire danger indices accepting at least hourly input data may allow reasonable fire danger calculations under these circumstances.

Drought-induced vegetation responses are often hypothesized as one of the key drivers of hydrological changes under multiyear droughts. However, until now, this hypothesis has not been systematically tested on areas that experienced significant drought-induced reductions in streamflow generation. Our results do not support this hypothesis and suggest that vegetation changes are unlikely to be the main driver of observed hydrological changes.We employed multiple remotely sensed vegetation indices (AVHRR NDVI & fPAR, MODIS NDVI & EVI, and Ku-VOD from multiple microwave satellite sensors) and rainfall-runoff shift indicators to investigate vegetation responses and their influences on streamflow generation during the Millennium Drought (from 1997 to 2009) in 156 catchments in Victoria, Australia. Many of these catchments experienced significant shifts in their rainfall-runoff relationship by severely reducing streamflow generation during the Millennium Drought. However, we show that vegetation indices are statistically similar or higher in many catchments during the Millennium Drought compared to pre-drought, consistent with published literature. Moreover, the spatial pattern of increase in vegetation indices does not match the spatial distribution of hydrological shifts, measured by significant streamflow reductions for a given rainfall. We argue that vegetation response is unlikely to be a primary driver of the observed hydrological shifts, although they are regarded as crucial in determining hydrological behaviour more generally. This finding has important implications for better understanding and modelling hydrological responses under future climate changes.

Montane peatlands are highly sensitive to climate change and disturbance, and their hydrological functioning strongly controls the transport of dissolved substances. Electrical conductivity (EC) serves as an integrative tracer of runoff generation processes and source contributions. This study analyzes long-term changes in EC-discharge (EC-Q) dynamics in response to climate warming and a multi-year drought in the Rokytka peatland, Central Šumava Mountains (Czechia) in response to climate warming and a multi-year drought. The drought is treated as a stress-test period that reveals the sensitivity and dominant response pathways of the system, indicating the likely direction of change as heat and drought intensify under climate warming.We use a unique 20-year dataset of 10-minute measurements of discharge, EC, and meteorological variables. Runoff events were classified by antecedent wetness and event structure, and water circulation patterns were analyzed using event-scale EC-Q hysteresis loops characterized by loop direction and morphology. Events were further compared across seasons and major climatic and management phases.Results show a pronounced shift after the onset of the warm and dry period in 2015–2018. Discharge regimes exhibit higher variability, more frequent extremes, and lower baseflow. Hydrographs became steeper, with shorter response times, faster rising and falling limbs, smaller event runoff volumes, and more asymmetric shapes. EC dynamics changed consistently: maximum EC values decreased, event-scale EC contrasts weakened, and EC returned more rapidly to baseline after events.EC-Q hysteresis loops also changed markedly. Hysteresis indices decreased and separation between rising and falling limbs weakened, indicating reduced event-scale contrasts in solute sources and more uniform mixing. Loop direction shifted toward more frequent clockwise patterns after 2015, consistent with earlier flushing followed by dilution. Together, these changes point to faster runoff generation and altered solute mobilization under warmer and drier conditions.The study demonstrates that long-term high-frequency EC monitoring provides a sensitive indicator of climate- and management-driven changes in peatland hydrology. EC-Q hysteresis analysis offers a powerful tool for diagnosing shifts in runoff generation, storage, and solute transport, and for evaluating the effectiveness of peatland restoration under a changing climate.

T occurrence of dry & wet events causes major adverse impacts in the Canadian Prairies. In the past, dry events, which are typically agricultural and/or hydrological droughts, have been common in the region. At least five major drought episodes have occurredin the Canadian Prairies during the past 120 years. These include multi-year droughts in the 1890s, 1910s, 1930s, late 1950s to early 1960s, 1980s, 1999-2005, 2009-10. The years 2001-2004 resulted in one of the largest area multi-year drought. Almost half of the agricultural prairies were in severe drought or worse during 2001. For the older droughts of the 1900 to 1950 period, the 1930s were the largest multi-year droughts, and 1961 and 1919 were the single-year severe droughts that covered the largest area. According to Bonsal et al. (2011), some of the major droughts have migrated into the Canadian Prairies from the United States Great Plains, including the 1999-2005 drought. This means that it is important to monitor the northern US droughts for expansion or migration into Canada.In the future, the frequency of both droughts and intense precipitation areexpected to increase. In fact, the review by Wheaton et al. (2013) found that (i) multi-year droughts (e.g., 5 to 10 years, or so) would occur more than twice as often forthe period to 2100; (ii) they would come with more evaporative power and be more intense as they will have much higher temperatures and much longer warm seasons; and (iii) they would cover much more area than even the across-Canada drought of 2001-2002. Droughts of such magnitudes would have devastating impacts on the Prairies, economically, environmentally, and socially, particularly on those industries where weather is a major determining factor to their survival and performance. One such industry is agriculture. It is the contention of this paper that estimation of impacts of the past droughts has been limited in scope, and may have underestimated these impacts. This under-estimation may be a result of several reasons: (i) Past studies have typically measured these impacts for only the drought period. In reality a drought would affect some of the enterprises (such as livestock production) that take several years to completely result in an economic gain to the producers. (ii) Although private costs of the people impacted by droughts are measured, the macro-level changes causing hardships to people and businesses are not measured. (iii) Droughts may impact ecological goods and services which can then affect the society at large. (iv) Loss to human capital through stress, sickness, and loss of employment as well as other changes that lead to lost productivity are typically not included. (v) Fiscal costs to the governments and their resulting impact on other programs have not been estimated. (vi) Economic hardships to smaller communities and people living therein have also not been addressed. We recommend that future investigations attempt to redress these deficiencies in the method of estimation of social, environmental and economic impacts of droughts. Impacts of the recent severe droughts in the US Plains and Canadian Prairies are reminders that current adaptation can be improved.

Recent climatic trends have increased forest fire activity in Canada. This study aimed to evaluate how forest fire conditions might evolve across the Canadian boreal forests in the future and to inform discussions about the impact of climate change on fire danger and severity. I generated surfaces of daily climate conditions using daily observational data from meteorological stations across Canada from 1976 to 2014. Simulated daily values of the same climatic variables were obtained from four earth system models of the Coupled Model Intercomparison Project Phase 5 project (CMIP5) for the historical period 1976–2005. Daily climate values for 2006–2100, forced by three climate change scenarios, Representative Concentration Pathway (RCP) 2.6, RCP 4.5, and RCP 8.5, were also simulated by the models. The simulated data were bias‐corrected and delta‐downscaled to project future trends in fire activity to assess the spatiotemporal variations of the potential impacts of climate change on forest fires. My results suggest fire danger and severity would increase in many Canadian boreal forests under RCP 8.5. The changes in fire conditions under RCP 2.6 were the least noteworthy; RCP 4.5 was associated with medium‐level changes.

Accurately predicting wildfire behavior at geographical-to-regional scales using coupled atmosphere-fire models has the potential to enhance the operational activities of Météo-France, which provides fire danger assessment in support of the French civil protection services. Current fire danger indices primarily rely on meteorological variables and do not include an explicit representation of biomass fuels, despite the fact that extreme wildfire events often result from the combined effect of atmospheric conditions and fuel state.In this study, we investigate how to integrate a detailed representation of surface fuels into the coupled Meso-NH/BLAZE modeling system (Lac et al., 2018; Costes et al., 2021), by taking advantage of high-resolution vegetation modeling from the SURFEX land surface system (Masson et al., 2013) and by defining fuel models for the vegetation types of the ECOCLIMAP database (Faroux et al. 2013). This study focuses on the French Mediterranean area for two main reasons: i) this is a wildfire-prone area that has experienced intense fire activity in recent years and that is projected to face increased fire danger due to climate change in the next decades (Fargeon et al. 2020); and ii) it has been monitored for several decades by the ONF (French forest services) through a dense observational network, providing extensive measurements of Live Fuel Moisture Content (LFMC).We implement the Rothermel heterogeneous rate-of-spread (ROS) formulation (Andrews, 2018) in the coupled atmosphere-fire model associated with dynamic fuel models (Scott and Burgan, 2005), in order to represent both dead and live components of the biomass fuels, and to dynamically transfer the herbaceous fuel load from live to dead components as a function of the LFMC to reproduce seasonal curing. We thus analyze the added value of including a live component of biomass fuels and the role of the LFMC in the ROS predictions. Preliminary results indicate that accounting for the live fuel component part of fuels generally reduces the simulated ROS, as higher live fuel content tends to inhibit combustion. Moreover, simulations using dynamic fuel models propagate less extensively than non-dynamic fuel models.Beyond the explicit modeling of fire-fuel interactions, we also examine the Fire Weather Indices (FWI) based on the Canadian approach (Van Wagner et al., 1985) and adopted by Météo-France to assess meteorological fire danger. By analyzing their relationship with simulated ROS, we aim to establish a first quantitative link between fire danger indicators and physically-based fire behavior predictions.