Fire Weather Index Projections Reveal Rising Wildfire Danger Across Northern South America

Wildfire danger in northern South America is set to intensify dramatically as the century progresses, according to a new study that used high-resolution climate projections to track fire-favorable weather across Colombia and Venezuela through 2100. The research, published in Environmental Challenges, applied the Canadian Fire Weather Index (FWI) to daily climate simulations from 19 downscaled CMIP6 models, revealing that the most hazardous conditions will concentrate in the same places they occur today, chiefly the La Guajira Peninsula and the Caribbean coasts of both countries, but will become far more frequent, persistent, and severe under higher emissions.

The FWI is the world’s most widely adopted benchmark for assessing atmospheric conditions that promote wildfire ignition, spread, and intensity. Developed by the Canadian Forest Service, it integrates four meteorological variables: air temperature, relative humidity, precipitation, and wind speed. Through a chain of intermediate components, including the Fine Fuel Moisture Code, the Duff Moisture Code, the Drought Code, and the Initial Spread Index, the index captures how readily surface fuels dry out and how fast flames could travel once ignited. Because these components interact nonlinearly, small concurrent shifts in temperature or moisture can produce disproportionate jumps in fire danger during prolonged dry spells.

A central challenge for regional fire-risk studies is that global climate models are too coarse and too biased to represent local fire weather reliably. To overcome this, the researchers turned to the NASA Earth Exchange Global Daily Downscaled Projections dataset, known as NEX-GDDP-CMIP6, which applies statistical bias correction and spatial disaggregation to CMIP6 simulations, producing daily data on a 0.25-degree grid. The team evaluated 19 models from this ensemble against ERA5-Land reanalysis data for the historical period 1980 to 2014, using mean bias, root mean square error, and Pearson’s correlation to judge how faithfully each model reproduced the four variables feeding the FWI.

The validation results were revealing. Temperature emerged as the best-simulated variable, with correlations between roughly 0.92 and 0.94 across individual models, reflecting the fact that surface temperature is governed mainly by the surface energy balance and large-scale circulation, processes that general circulation models handle well. Wind speed and relative humidity performed moderately, while precipitation proved the weakest link, with correlations of only about 0.52 to 0.58. This is unsurprising: tropical precipitation depends on deep convection, moisture transport, cloud microphysics, and interactions with the complex Andean topography, all of which must be approximated through parameterizations that vary from model to model.

Crucially, no single model outperformed the others across all variables and metrics. Instead, the multi-model ensemble mean delivered the lowest errors and the highest correlations for every variable, reaching 0.95 for temperature, 0.79 for wind speed, 0.73 for relative humidity, and 0.63 for precipitation. By averaging out the idiosyncratic errors of individual simulations, the ensemble provided the most robust foundation for the fire danger projections, though the authors caution that uncertainty in precipitation and moisture-related variables still propagates through the nonlinear structure of the FWI and should temper interpretation of the results.

The historical baseline confirmed a pronounced seasonal rhythm in fire weather. During December through February, the dry season, Moderate and High hazard categories covered 48 percent and 31 percent of the study area respectively, with the highest index values concentrated over La Guajira, the Colombian Caribbean coast, and northern Venezuela. By June through August, the Low category dominated 96 percent of the domain as the wet season peaked, and September through November remained similarly benign. This cycle is orchestrated by the seasonal migration of the Intertropical Convergence Zone and the northeasterly trade winds, which together control when fuels dry and when moisture returns.

The projections for 2025 to 2100 show that climate change amplifies this seasonal cycle rather than erasing it. Under the low-emission SSP1-2.6 scenario, the Low category still covers 87 percent of the region on average, but under the high-emission SSP5-8.5 pathway it shrinks to 64 percent, while the Moderate category expands to 35 percent and High hazard appears for the first time in the mean conditions. The contrast is even starker for extreme events: the Very High category dominates 66 percent of the study area during extreme weather under SSP1-2.6, rising to 74 percent under SSP2-4.5 and 83 percent under SSP5-8.5, a clear signal that radiative forcing expands the territory exposed to the most dangerous fire weather.

Seasonally, the changes concentrate almost entirely in the December-February dry season, with smaller shifts in March through May. Under SSP5-8.5, High-risk conditions during the dry season reach 49 percent of the region and Very High risk emerges at 17 percent, while the wet-season months remain overwhelmingly Low-risk across all scenarios. The authors attribute this pattern to a reorganization of hydroclimatic processes over the tropical Atlantic: anthropogenic warming enhances tropospheric stability and suppresses deep convection, while an intensifying Caribbean Low-Level Jet and an expanding North Atlantic Subtropical High promote the advection of dry, subsiding air. The result is a growing propensity for flash droughts, in which abrupt increases in vapor pressure deficit strip moisture from fine fuels to critical flammability thresholds even without extreme rainfall deficits.

The study’s implications reach well beyond climate modeling. Because the FWI does not account for vegetation continuity, topography, or ignition sources, which in the Neotropics are predominantly human-caused, the projections should be read as an intensification of fire-favorable meteorology rather than forecasts of individual fires. Even so, the persistent identification of La Guajira, the lower Colombian Caribbean basin, and the northern arc of Venezuela as danger hotspots offers a quantitative basis for shifting from reactive firefighting toward anticipatory risk management, including early-warning infrastructure, preventive prescribed burns, and pre-season mobilization of resources. The urgency is underscored by recent history: carbon emissions from fires in Venezuela during the 2024-2025 seasons were roughly 50 percent above the historical average, and about 15 percent of the region’s páramo habitat burned between 1985 and 2022.

This is the first comprehensive FWI assessment for northern South America built on NEX-GDDP-CMIP6 projections, and it delivers a quantitative baseline of atmospheric fire hazard independent of the stochastic variability of human ignitions. The message for the region is sobering but actionable: the climate signal for wildfire danger emerges early, meaning even moderate warming can expand fire-favorable conditions before any dramatic shift in annual rainfall. As the authors note, integrating these meteorological projections with dynamic vegetation models, fuel loads, land-cover change, and socioeconomic ignition patterns remains the next frontier, but the framework now exists to put climate-informed fire danger at the center of land-use planning and cross-border adaptation strategy in one of South America’s most ecologically diverse corners.

Subject of Research: Projection of forest fire hazard in northern South America using the Fire Weather Index driven by NEX-GDDP-CMIP6 climate models

Article Title: Projection of Forest Fire Hazard in Northern South America Using the Fire Weather Index Driven by NEX-GDDP-CMIP6 Climate Projections

Article References: Guerra, Y., Arregocés, H. A., & Rojano, R. (2026). Projection of Forest Fire Hazard in Northern South America Using the Fire Weather Index Driven by NEX-GDDP-CMIP6 Climate Projections. Environmental Challenges, 25, Article 101659. https://doi.org/10.1016/j.envc.2026.101659

Image Credits: AI Generated

DOI: 10.1016/j.envc.2026.101659

Keywords: wildfire, Fire Weather Index, CMIP6, NEX-GDDP, climate change, Colombia, Venezuela, La Guajira, SSP scenarios, precipitation, drought, fire danger