The first of the two simulations is a historical reconstruction. The team took the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis, known as ERA5, which blends observations with a global forecast model to create a physically consistent record of the recent past, and used it to drive the Weather Research and Forecasting model, or WRF, over the full South American domain for the period 2000 to 2021. Because the model grid is only 4 kilometers across, deep moist convection, the process that builds towering cumulonimbus clouds and produces intense rain, hail, and lightning, can be resolved directly by the model’s dynamics. This matters because traditional climate models must parameterize convection, and those parameterizations are a leading source of error in simulating the timing, intensity, and location of rainfall, particularly over complex terrain like the Andes and over the Amazon, where the diurnal cycle of convection is notoriously difficult to capture.

To test whether the simulation was trustworthy, the researchers validated it against a battery of independent satellite and reanalysis products covering precipitation and near-surface air temperature. The results were striking: the 4-kilometer simulation captured South America’s climate across an enormous range of scales, from the slow interannual variations tied to phenomena like the El Niño-Southern Oscillation, through the annual march of the South American monsoon, down to the hour-by-hour rhythm of afternoon thunderstorms. Crucially, the downscaling demonstrated clear added value over the original ERA5 data itself, especially at daily to sub-daily time scales and at mesoscale to local spatial scales. In other words, the fine-grid model did not merely reproduce its coarse driving data; it genuinely improved the representation of the processes that matter most for floods, droughts, agriculture, and water management.

The second simulation looks toward the end of the century using an elegant technique called the Pseudo-Global Warming, or PGW, approach. Rather than running a full coupled climate model into the future, the team kept the historical weather sequence from ERA5 but perturbed the meteorological fields with monthly climate change signals drawn from the Community Earth System Model Large Ensemble, known as LENS2. The perturbations correspond to roughly 3 degrees Celsius of global warming above preindustrial levels under the CMIP6 SSP3-7.0 emissions scenario, representative of conditions expected during the 2060 to 2080 period. The advantage of this method is that the future simulation experiences the same weather patterns as the historical one, only embedded in a warmer atmosphere, which makes differences between the two runs directly attributable to the climate change signal rather than to the chaos of natural variability.

The projections that emerge are sobering. The PGW simulation shows significant continental-scale warming, with the strongest temperature increases concentrated over the Andes, broadly consistent with the underlying LENS2 projections. This elevation-dependent warming in the Andes carries particular weight because the region’s snowpack and glaciers act as natural water towers for millions of people downstream. Indeed, the simulation projects declines in both snowfall and snowpack across the Andes, a finding that aligns with a growing body of observational evidence of shrinking snow persistence and retreating cryosphere in the region, and one with direct implications for the water supplies of cities such as Santiago, Lima, and Bogotá.

Precipitation changes prove far more spatially and seasonally complex than the temperature signal. Most regions of the continent experience either modest increases or slight decreases in total rainfall, but one region stands out: the Amazon Basin exhibits predominant drying during the austral summer, the season when the rainforest’s own convective recycling normally sustains the wet season. This projected summer drying echoes concerns raised by earlier studies about the strengthening of the Amazonian dry season and the vulnerability of the forest to a self-reinforcing cycle of drought, fire, and degradation. Because the Amazon recycles a large fraction of its own rainfall and exports moisture eastward and southward through low-level jets often described as aerial rivers, changes in the basin’s water balance can propagate far beyond its borders, affecting agriculture in the La Plata basin and beyond.

Perhaps the most robust and consequential finding concerns extremes. Across the continent, extreme precipitation intensifies in the warmer climate, consistent with the basic thermodynamic principle that a warmer atmosphere holds roughly 7 percent more water vapor per degree of warming, loading the dice toward heavier downpours even where mean rainfall changes little. For a continent already familiar with devastating floods in southeastern Brazil and Argentina, gargantuan hailstorms on the Argentine pampas, and deadly landslides in the Andean foothills, an intensification of hourly rainfall extremes represents a substantial escalation of hazard. The convection-permitting framework is especially valuable here, because it resolves the mesoscale convective systems, vast organized storm complexes that can span hundreds of kilometers, responsible for much of South America’s extreme rainfall and severe weather.

The dataset itself, dubbed SAAG, is openly available through the NCAR GDEX system and the Chilean National Laboratory HPC system, but its sheer scale presents a paradox. The raw WRF output for both the historical and future simulations amounts to approximately 2 petabytes, far too large for individual research groups to copy locally. The authors argue that establishing centralized, high-performance analysis infrastructure in South America, comparable to platforms such as the UK Met Office’s JASMIN or Germany’s Levante system, is urgently needed. Without such infrastructure, they caution, datasets of this magnitude cannot fully support the climate science, impact studies, and policymaking in the very region they describe, a gap that highlights persistent inequities in global scientific computing capacity.

For South American scientists, water managers, and policymakers, the significance of this work is difficult to overstate. The continent hosts the planet’s largest tropical forest, its driest nonpolar desert, and mountain ranges whose snow and ice sustain major river systems, all within a single modeling domain that can now be examined at storm scale over multiple decades. The simulations open the door to detailed studies of atmospheric convection, land-surface feedbacks, moisture recycling, and hydrological processes, both in the present climate and under a substantially warmer one. As the world approaches the warming levels projected in these runs, the SAAG dataset offers the most detailed window yet into how South America’s extraordinary climates, and the hundreds of millions of people who depend on them, may be transformed in the decades ahead.

Subject of Research: Convection-permitting dynamical downscaling of present and future South American climate at 4-km resolution

Article Title: Multi-decadal convection permitting dynamical downscaling of current and future climates over South America

Article References: Liu, C., Ikeda, K., Dominguez, F., Prein, A. F., Rasmussen, R. M., Zhang, Z., Xue, L., Neale, R. B., Chun, K. P., He, C., Rios-Berrios, R., Reboita, M. S., Huang, Y., Gomes, H. B., Llopart, M., Dudhia, J., Tian, Y., Scaff, L., Varble, A. C., … Gutmann, E. D. (2026). Multi-decadal convection permitting dynamical downscaling of current and future climates over South America. Climate Dynamics, 64(10), Article 435. https://doi.org/10.1007/s00382-026-08376-w

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08376-w

Keywords: South America, dynamical downscaling, convection-permitting modeling, WRF model, pseudo-global warming, climate change, Amazon Basin, Andes, extreme precipitation, snowpack, ERA5, Climate Dynamics

The finding matters because winter is not the dormant period it is often assumed to be. Beneath a blanket of snow, soils remain biologically active. Snow acts as an insulating layer, decoupling soil temperatures from frigid air temperatures and preventing the ground from freezing to depths that would kill or immobilize microbial communities. When snow lingers, microbes continue to decompose organic matter, respire carbon dioxide and transform nitrogen compounds at measurable rates throughout the cold season. In temperate and boreal forests, this winter-under-snow activity has been shown in earlier research to contribute a substantial fraction of annual carbon losses from soils. What the new study adds is evidence that in dryland systems — where snow is intermittent, thin and vulnerable — the presence or absence of a living soil surface can determine whether that insulating blanket persists at all.

The research, led by Yuqing Cao, Bowker, Zhao, Chamizo, Delgado-Baquerizo and colleagues under the title ‘Moss biocrusts sustain snowpack and soil function in cold deserts’, draws on long-term field monitoring of how moss-dominated biocrust cover influences both the duration and the depth of snow cover. The authors document that surfaces clothed in moss biocrusts hold snow longer and maintain deeper snowpack than adjacent uncrusted ground. The mechanism is partly physical. Moss biocrusts create a rough, porous microtopography at the soil surface, with elevated tufts and hollows that trap drifting snow and reduce wind-driven sublimation and redistribution. In open cold deserts, where wind is a dominant agent of snow loss, this roughness effect can make the difference between a snowpack that survives weeks of winter and one that vanishes within days.

There is also a thermal dimension. By retaining snow, biocrusted surfaces maintain a more stable and generally milder soil temperature regime through winter. The snow layer itself acts as insulation, and beneath it the dark, structurally complex biocrust surface absorbs and redistributes energy differently than pale, bare sediment. The consequence, as the study and the accompanying commentary by Lafuente emphasize, is that microbial activity in the soil below biocrusts continues at meaningful levels during months when uncrusted soils may freeze solid. Soil biogeochemistry — the sum of decomposition, respiration, nutrient mineralization and microbial transformations — is thus sustained rather than suspended.

This sustained activity has direct implications for the carbon cycle of cold deserts. Drylands collectively store large reservoirs of organic carbon in their soils, and biocrusts themselves are significant contributors to those reservoirs, fixing carbon dioxide through photosynthesis during moist periods and delivering it to the soil as organic matter. Winter is a season in which the balance between carbon input and carbon loss is delicate. When snow insulates the surface, heterotrophic microbes respire stored carbon slowly but steadily; when snow is absent and soils freeze deeply, physical and biological processes change abruptly, and freeze-thaw cycles can release pulses of carbon dioxide and nitrous oxide while damaging microbial cells and destabilizing aggregates. By keeping snow on the ground, moss biocrusts appear to buffer these dynamics, maintaining conditions under which soil functions proceed in a more continuous, less perturbed fashion.

The broader context of this work is the well-documented vulnerability of snow cover in a warming climate. Satellite records and ground observations across the Northern Hemisphere have documented declining snowpack extent, depth and duration, and projections consistently indicate further losses as winters warm. Research on snow drought has shown that human-caused warming has already reduced snowpack in many mountain regions, and studies of radiative forcing by dust and dark particles on snow have long demonstrated how small changes at the snow surface can accelerate melt. What the new study makes clear is that snow loss in cold deserts is not only a story about climate and atmosphere; it is also a story about the ground surface itself. Losing biocrusts removes a biological mechanism of snow retention precisely when climatic change is already eroding snow cover from the other direction — a compounding of stresses that could accelerate the degradation of dryland soils.

Biocrusts are, in fact, among the most threatened surface communities on the planet. Syntheses of global change effects have documented their sensitivity to warming, altered precipitation, and especially physical disturbance from livestock trampling, off-road vehicles, energy development and human foot traffic. Recovery is slow: cyanobacteria-dominated crusts may re-form in years to decades, while moss and lichen communities characteristic of cooler, more stable drylands can require centuries. Global assessments estimate that a large fraction of the world’s biocrusted area is already degraded. The new findings give that loss an additional dimension of concern. If biocrust destruction shortens snow cover duration in cold deserts, it exposes soils to deeper freezing, suppresses winter microbial activity, and potentially diminishes the very carbon and nitrogen inputs on which dryland ecosystems depend — a feedback loop in which surface degradation and soil function decline reinforce one another.

The study also reframes how scientists and land managers should think about seasonality in drylands. Much biocrust research has focused on the growing and rainfall seasons, when crusts are photosynthetically active and most visible in their influence on erosion and nutrient cycling. The winter findings shift attention to a period that has been comparatively neglected in dryland research, in part because cold deserts sit at the intersection of two disciplines: snow hydrology, which has traditionally focused on forests, mountains and tundra, and dryland ecology, which has traditionally focused on heat and aridity. By demonstrating that the two domains are physically and biologically coupled through the soil surface community, the work argues for integrating biocrust cover into models of snow dynamics, soil frost and winter carbon flux in cold deserts — regions that include substantial areas of the intermountain western United States, central Asia and high-altitude plateaus.

Writing in Nature Geoscience, Lafuente situates the study within this larger agenda, noting that biocrusts can substantially enhance snow retention and thereby sustain soil biogeochemistry, microbial activity and soil ecosystem functions in cold deserts. The commentary, which accompanies the research under the title ‘Winter carbon cycling beneath biocrusts’, underscores that the findings emerge from a long-term field program — a point worth emphasizing, because capturing interannual variability in snow depth, snow duration and soil response requires years of patient measurement in environments that are logistically demanding to monitor. It is precisely this kind of sustained observation that allows the causal chain from surface cover, to snowpack persistence, to winter soil function to be traced with confidence.

The implications reach toward both conservation and climate science. For land managers in cold deserts, protecting biocrusts from trampling and disturbance acquires a new rationale that goes beyond erosion control: intact moss biocrusts are, in effect, natural snow-management infrastructure. For Earth system modelers, the study suggests that the representation of dryland winter processes is incomplete without a term for biological surface cover and its effect on snow retention and soil thermal regimes. And for carbon accounting, the message is that the winter months in cold deserts — long treated as a blank interval between growing seasons — host active, cover-dependent biogeochemistry that could shift substantially as both climate and land use change. A crust of mosses a few millimeters thick, the study shows, quietly governs whether the soil beneath it sleeps through winter or keeps working — and with it, whether carbon in cold desert ecosystems remains stored or begins to move.

Subject of Research: Influence of moss biocrusts on snow retention and winter soil carbon cycling in cold deserts

Article Title: Winter carbon cycling beneath biocrusts

Article References: Lafuente, A. (2026). Winter carbon cycling beneath biocrusts. Nature Geoscience, 19(9), 1004-1005. https://doi.org/10.1038/s41561-026-02084-0

Image Credits: AI Generated

DOI: 10.1038/s41561-026-02084-0

Keywords: biocrusts, cold deserts, snowpack, carbon cycle, soil biogeochemistry, microbial activity, moss, drylands, soil insulation, climate change, ecosystem ecology, Nature Geoscience