Abstract At 20:20 UTC on March 16 th , 2024, the Sundhnúksgígar crater row located north of the town of Grindavík on the Reykjanes Peninsula, Iceland, erupted. Forty minutes after the start of the eruption, a significant rain shower started 20 km downwind of the eruption site to the west of Keflavík International Airport. Since there was no precipitation over the peninsula prior to the eruption and the precipitation event started shortly after the eruption and downwind from the volcano, we were led to believe that it was linked to the eruption. In the style of a mystery novel, we sought to elucidate the mechanism linking the eruption and the rain shower. Two different mechanisms were initially investigated: 1) the volcano heat and moisture lead to convection and 2) the volcanic ash created condensation nuclei. Using radar data, ground-based measurements and model soundings, it was found that the eruption could not be directly responsible for the precipitation event through either of these mechanisms. As such, another process had to be involved, namely that the eruption acted as an obstacle to the atmospheric flow causing precipitation.

Abstract Wildfire activity in the southwestern United States has intensified in recent decades, driven by the complex interactions of climatic variability, vegetation patterns, and human impacts. This study examines wildfire dynamics in Arizona and New Mexico using data from 1984–2021 to evaluate how antecedent moisture and aridity conditions influence fire activity across conifer forests, shrublands, and grasslands. Findings reveal distinct, ecosystem-specific responses to climate: in conifer forests, prolonged drought and rising vapor pressure deficits drive larger and more severe wildfires, underscoring the increasing influence of aridity. In shrublands and grasslands, wildfire risk is often tied to antecedent wet periods that stimulate fine fuel growth, followed by warm, dry conditions that promote fire spread. The spread of invasive grasses has further heightened fire risk in shrubland and desert ecosystems by enhancing fuel connectivity and transforming fire-climate dynamics in historically fuel-limited regions. As the climate continues to warm and precipitation patterns shift, the spatial and temporal patterns of wildfire activity are expected to remain dynamic, posing significant challenges for fire management and planning. Additionally, the ongoing expansion of the wildland-urban interface will amplify the social and ecological consequences of wildfires, regardless of whether conditions trend wetter or drier. This study highlights the need for adaptive management strategies that incorporate short-term climatic influences into fire risk assessments while addressing the unique ecological and societal contexts of the region. By advancing understanding of fire-climate-vegetation interactions, this research provides critical insights for mitigating future wildfire impacts in the Southwest.

Abstract The temperate climate region of southeastern Australia (SEA) suffers from large periodic wildfires. We investigated how land-atmosphere (L–A) interactions could affect wildfires in the SEA region by applying the Forest Fire Danger Index (FFDI) using climate variables from the European Center for Medium-Range Weather Forecasts Reanalysis 5. We calculated FFDI95, which is the number of days exceeding the 95th percentile of daily FFDI during the study period of 1980–2021. The FFDI95 was verified by correlation with the burned areas obtained from satellite data and fire records (r = 0.66, p-value < 0.05). We found that FFDI95 in the temperate climate region of SEA increased significantly during the fire season (austral summer) throughout the study period. Using the FFDI95 area averaged over the study region, correlation and composite difference analyses were conducted along with land and atmospheric variables after removing the long-term trend and El Niño-Southern Oscillation variability. During the pre-fire season (austral spring), significantly reduced soil moisture enhances heat transfer through sensible heat flux, thus raising the temperature from the surface to the lower troposphere. Thermal expansion results in increased atmospheric thickness and strengthened anticyclonic circulation in the mid-troposphere. During the fire season, a thicker troposphere, including the intensification of anticyclonic circulation and subsidence, may promote hot and dry conditions, thus intensifying wildfires. The physical processes related to the variations in land conditions and the corresponding responses of the atmosphere indicate that L–A interactions can amplify wildfires in SEA.

Abstract Wildfires occur each summer in the boreal forests of Alaska, with an increasing frequency of extreme fire seasons in recent decades. The wildfire season typically begins after the snow melts (i.e., snowoff) in April–May, which is trending toward earlier dates since 1959 (ranging from 2 to 4 days decade−1 over Alaska). This study evaluates snowoff dates in Alaska and related synoptic-scale atmospheric drivers in spring over 1959–2020 to assess possible linkages with the summer wildfire season. Many of the largest fire seasons followed regional snowoff dates in the earliest tercile accounting for 56%–95% of the total historical area burned by the region. Snowoff is best correlated with average daily maximum temperatures during April–May with weaker correlations thereafter. In some years, early snowoff and associated warm temperature anomalies persisted later into the summer influencing fire danger indices. This occurred in many years with the largest area burned. More limited instances of persistent lower precipitation anomalies were also found. The persistent temperature anomalies primarily occurred during El Niño conditions and the positive phase of the east Pacific/North Pacific pattern. Precipitation anomalies were most strongly associated with the Atlantic multidecadal oscillation. Blocking high pressure associated with these teleconnections was a likely driving mechanism, particularly for temperature persistence. The results indicated that the snowoff date and concurrent springtime synoptic climate conditions may provide predictability of fire weather conditions during the wildfire season when this persistence occurs. These subseasonal surface–atmosphere linkages could be used to inform wildfire-related seasonal forecasts. Significance Statement The purpose of this study is to understand how snowoff timing impacts seasonal wildfire activity in Alaska to inform wildfire-related forecasts needed for operational planning. Snowoff timing was found to directly impact fire weather conditions only during the early season. However, early snowoff was correlated with sustained warm temperature anomalies during several large wildfire years. These conditions were linked with El Niño and other teleconnections. Sustained dry conditions were most strongly associated with wildfire on the North Slope. Our results show that climate conditions during the spring snowoff period may serve as a potential predictor of summer temperature, precipitation, and wildfire in Alaska. These precursor relationships can therefore contribute to improvements in the seasonal prediction of wildfire danger.

Abstract Soil erosion is a widespread form of soil degradation in terrestrial ecosystems and plays a crucial role in the dynamics of soil carbon pools. Assessing soil erosion affected by climate and land-use changes is essential for evaluating future risks and impact on soil organic carbon (SOC) displacements. The phase 5 of the Coupled Model Intercomparison Project (CMIP5) simulations have provided the basis for most such assessments, but are gradually being superseded by more recent simulations from phase 6 of CMIP (CMIP6). However, a quantitative comparison of the differences between CMIP5 (RCP8.5) and CMIP6 [shared socioeconomic pathway (SSP) SSP5-8.5] models and their impacts on soil erosion and SOC simulations has not been conducted. Therefore, this study aims to compare changes in soil erosion in response to climate change and land-use change in China based on CMIP5 and CMIP6 simulations and assesses the impact of erosion on SOC stocks. Combining the effects of climate and land-use change, the CMIP5 ensemble model projects an increase in soil erosion rates over most of China, while CMIP6 models project an average soil erosion reduction of 39 t km−2 a−1 for the years 2031–50 compared to the reference period. Climate and land-use changes contribute to the increased soil erosion rate by 51.75% and −28.85%, respectively, based on CMIP5 and by 32.75% and −54.01%, respectively, based on CMIP6. The CMIP6 results demonstrate less rainfall erosivity due to climate change and more pronounced mitigating effects from beneficial land-use changes on soil erosion compared to CMIP5. However, the average change in SOC displacement rate is projected to be −0.02 t km−2 a−1 for CMIP6. The CMIP5 results suggest that soil erosion in areas other than the Tibetan Plateau will result in a rising rate of soil organic carbon displacement by 0.03 t km−2 a−1. Therefore, it is recommended that decision-makers consider multiple dimensions such as different models and influencing factors when updating impact studies for water and soil conservation.

Abstract This study examines climate conditions that modulate crop yield using a satellite vegetation color index in the highlands of South Africa 27°–30°S, 24°–29°E. A monthly time series is formulated (1982–2022) which exhibits large seasonality (brown winters, green summers). Correlations with detrended national maize yield exceed 0.70 in austral summer. The January–March vegetation index exhibits significant negative correlation with east Pacific and west Indian sea surface temperatures at lead times from 0 to 6 months. Persistent 3–5-yr cycles are associated with tilting of the ocean thermocline and El Niño–Southern Oscillation (ENSO), a link that has strengthened with time. Green minus brown composites exhibit a cyclonic circulation near Windhoek and a midlatitude anticyclone. Together these induce easterly winds (3 m s−1) that supply moisture from the Mozambique Channel. The composites show a southward shift of upwelling in the Benguela Current and a slowing and warming of the Agulhas Current. Long-term simulations by the CMIP6 ensemble predict more rain in the east and warm temperatures (+0.04°C yr−1) in the west. Yet, outcomes suggest that adaptation to climate change is underway and that South Africa’s crop yields may continue to rise (+0.1 t ha−1 yr−1) and ensure regional food security.

Abstract Shallow landslides are often triggered during rainfall events, which can increase subsurface soil water pressure and destabilize hillslopes. The likelihood of regional shallow landslide initiation is often assessed through a comparison of rainfall intensity and duration to pre-established thresholds. While informative for landslide warning, this exclusive focus on rainfall exceeding thresholds does not consider the meteorological conditions producing the rainfall. Here, we ask the question, are there common meteorological characteristics that lead to landslide-triggering precipitation? We develop a catalog of 18 post-1995 widespread, impactful shallow landslide events occurring within 13 storms across California, USA, where initiation time could be constrained to a ≤6-h window. We examine storm characteristics during the landslide initiation window using atmospheric reanalysis products, radar observations, and quantitative precipitation estimates. We find that, while there are some common atmospheric characteristics across landslide events, they can occur under a range of atmospheric conditions. For example, all Northern California landslide events assessed are associated with moderate to strong atmospheric rivers (ARs), while Southern California landslides feature non-AR to strong AR conditions. The storm events evaluated herein share many characteristics of hydrologically important storms in California that did not necessarily result in landslides; thus, atmospheric characteristics alone may not be sufficient to determine whether landslides will occur. However, documenting the characteristics of landslide-triggering storms defines the conditions under which landslides tend to occur, provides analog events that can be useful in forecast applications, helps define future research directions relating to atmospheric conditions and landslides, and supports interdisciplinary research efforts. Significance Statement Rainfall-triggered landslides pose a threat to communities situated in and around California’s steep terrain. Thresholds related to measured antecedent rainfall accumulation and anticipated rainfall intensity over various durations are typically used for predicting landslide occurrence. Here, we assess various atmospheric characteristics of 18 storms that triggered landslides to determine whether there are common characteristics that could provide insight into landslide occurrence beyond precipitation information. Our results indicate while there are some common characteristics across landslide events, the events can occur under a range of conditions. This finding and the documentation of these events are useful for communicating weather forecasts and potential hazards, help build an interdisciplinary understanding of landslide-triggering precipitation, and highlight future research needs.

Abstract Regional warming and associated changes in hydrologic systems pose challenges to water supply management in river basins of the western United States and call for improved understanding of the spatial and temporal variability of runoff. We apply a network of total width, subannual width, and delta blue intensity tree-ring chronologies in combination with a monthly water balance model to identify droughts and their associated precipitation P and temperature T footprints in the Truckee–Carson River basin (TCRB). Stepwise regression gave reasonably accurate reconstructions, from 1688 to 1999, of seasonal P and T (e.g., R2 = 0.50 for May–September T). These were disaggregated to monthly values, which were then routed through a water balance model to generate “indirectly” reconstructed runoff. Reconstructed and observed annual runoff correlate highly (r = 0.80) from 1906 to 1999. The extended runoff record shows that twentieth-century droughts are unmatched in severity in a 300-yr context. Our water balance modeling reconstruction advances the conventional regression-based dendrochronological methods as it allows for multiple hydrologic components (evapotranspiration, snowmelt, etc.) to be evaluated. We found that imposed warming (3° and 6°C) generally exacerbated the runoff deficits in past droughts but that impact could be lessened and sometimes even reversed in some years by compensating factors, including changes in snow regime. Our results underscore the value of combining multiproxy tree-ring data with water balance modeling to place past hydrologic droughts in the context of climate change. Significance Statement We show how water balance modeling in combination with tree-ring data helps place modern droughts in the context of the past few centuries and a warming climate. Seasonal precipitation and temperature were reconstructed from multiproxy tree-ring data for a mountainous location near Lake Tahoe, and these reconstructions were routed through a water balance model to get a record of monthly runoff, snowmelt, and other water balance variables from 1688 to 1999. The resulting extended annual runoff record highlights the unmatched severity of twentieth-century droughts. A warming of 3°C imposed on reconstructed temperature generally exacerbates the runoff anomalies in past droughts, but this effect is sometimes offset by warming-related changes in the snow regime.