Fog Frequency Research Articles

Decadal Regime Shifts in Sea Fog Frequency over the Northwestern Pacific: The Influence of the Pacific Decadal Oscillation and Sea Surface Temperature Warming

Sea fog significantly impacts marine activities, ecosystems, and radiation balance. We analyzed the decadal variation characteristics of sea fog frequency (SFF) over the northwestern Pacific and investigated the roles of the Pacific decadal oscillation (PDO) and sea surface temperature (SST) warming in driving these changes. The results show that SFF experienced a significant and sudden decadal increase around 1978 (up by 12.9%) and a prominent decadal decrease around 1999 (down by 7.8%). The sudden increase in SFF around 1978 was closely related to the PDO. A positive PDO phase induced unusual anticyclonic circulation and southerly winds over the northwestern Pacific, enhancing low-level atmospheric stability and moisture supply, thus facilitating sea fog formation. Nevertheless, the decrease in SFF around 1999 was related to SST warming in the north Pacific. The rise in sea temperatures weakened the SST front south of the foggy region, reducing the cooling and condensation of warm air necessary for sea fog formation. This study enhances the understanding of the decadal variability mechanism of SFF over the northwestern Pacific regulated by large-scale circulation systems and provides a reference for future sea fog forecasting work.

Clinical epidemiology of dengue and COVID-19 co-infection among the residents in Dhaka, Bangladesh, 2021-2023: A cross-sectional study

Abstract Background Co-infection of dengue and COVID-19 has increased the health burden worldwide. We found a significant knowledge gap in epidemiology and risk factors of co-infection in Bangladesh. Methods This study included 2458 participants from Dhaka city from December 1, 2021, to November 30, 2023. We performed Kruskal-Walli’s test and χ2 test. Multivariable logistic regression was also performed. Results Co-infection of dengue and COVID-19 was found among 31% of the participants. Co-prevalence of dengue and COVID-19 was found in higher frequency in Jatrabari (14%), and Motijhil (11%). Severe (65%, p-value 0.001) and very severe (78%, p-value 0.005) symptoms were prevalent among the participants aged >50 years. Long-term illness was prevalent among the participants with co-infection (35%, 95% CI 33%- 36%) and COVID-19 (28%, 95% CI 26%- 30%). Co-infected participants had a higher frequency of heart damage (31.6%, p-value 0.005), brain fog (22%, p-value 0.03), and kidney damage (49.3%, p-value 0.001). Fever (100%) was the most prevalent symptom followed by weakness (89.6%), chills (82.4%), fatigue (81.4%), headache (80.6%), feeling thirsty (76.3%), myalgia (75%), pressure in the chest (69.1%), and shortness of breath (68.3%), respectively. Area of residence (OR 2.26, 95% CI 1.96-2.49, p-value 0.01), number of family members (OR 1.45, 95% CI 1.08-1.87, p-value <0.001), and population density (OR 2.43, 95% CI 2.15-3.01, p-value 0.001) were associated with higher odds of co-infection. We found that coinfected participants had a 4 times higher risk of developing severe health conditions (OR 4.22, 95% CI 4.11-4.67, p-value 0.02). Conclusions This is one of the early epidemiologic studies of co-infection of dengue and COVID-19 in Bangladesh.

Urbanisation‐driven shifts in fog patterns and fog hole formation in the Indo‐Gangetic Plain

AbstractRecent studies indicate a global decline in fog occurrences, particularly in urban areas. This study investigates fog trends across the Indo‐Gangetic Plain, focusing on the impact of urbanisation using long‐term ground and satellite data. Despite a general increase in fog frequencies elsewhere, we find a notable decline in dense fog occurrences in the megacity Delhi. Satellite data reveal that expanding fog holes over major urban areas strongly correlate with the underlying urban and built‐up areas. These findings highlight the substantial role of urban expansion in altering fog patterns, with broad implications for aviation and other sectors reliant on accurate fog prediction.

Landscape Effects on Local Species Richness of Woody Specialists in Subtropical Montane Cloud Forest of Taiwan

ABSTRACTAimHow is the local species richness of woody specialists in vegetation plots located within subtropical montane cloud forests (SMCFs) affected by the landscape structure of the surrounding SMCF habitat patch?LocationSubtropical montane cloud forests in Taiwan.TaxonWoody species specialised in growing in foggy conditions.MethodsWe used plant occurrence data from major herbaria together with fog frequency data to identify fog specialists of SMCFs in Taiwan. Subsequently, we extracted 20 × 20 m forest vegetation plots from the National Vegetation Database of Taiwan and calculated the richness of woody specialists in each of them. Using a published predicted SMCFs distribution map, we estimated the landscape context of SMCFs around each vegetation plot within circular buffer zones of increasing radius. The variables of landscape structure include those related to the area of SMCFs habitat (area and connectivity), surrounding heterogeneity (topographical heterogeneity and vegetation diversity) and edge effect (the nearest distance from the plot to the edge and the edge length). The multiple linear regression model was used to investigate which of the three mechanisms of landscape context has the strongest effect on the local richness of fog specialists.ResultsOnly the area of SMCFs habitat patch shows a significant positive effect on the local species richness of woody specialists in the plot when considering all the landscape variables. Area per se might be a possible mechanism that supports this positive species‐area relationship. Additionally, the area of SMCFs patch is highly correlated with connectivity, indicating that larger SMCF patches enhance connectivity beyond buffer zones, sustaining species through the rescue effect from the regional species pool.Main ConclusionsPatch size and connectivity are crucial for the species richness of woody specialists in SMCFs in Taiwan. For conservation, we recommend protecting larger, less fragmented SMCF patches to maintain biodiversity.

Observed Climatology and Formation Mechanisms of Sea Fog Along the Trans‐Arctic Shipping Routes

AbstractAs Arctic sea ice rapidly melts, trans‐Arctic shipping routes are emerging with significant economic value and potentially reshaping global shipping patterns. The safety of ships navigating along these routes will be severely threatened by low visibility caused by Arctic sea fog. Here, we utilize ship and coastal site observations spanning 1979–2023 to investigate the climatological features and mechanisms of Arctic sea fog from June to September. We find that the Northern Sea Route (NSR, along the Russian coast) experiences a mean fog frequency of 20.0%, significantly higher than the 11.5% fog frequency observed along the Northwest Passage (NWP, along the Canadian coast). Fog frequency shows null correlation with sea ice but a strong negative correlation (−0.80) with surface air temperature. The lower mean surface air temperature in the NSR region enhances relative humidity and atmospheric stability, which are conducive to fog formation and maintenance. We further reveal that fog formation mechanisms differ between the NSR and NWP. Along the NSR, fog is usually advection fog, associated with upper boundary layer warming and moistening; in contrast, along the NWP, fog is typically radiation fog linked to near‐surface cooling. Our study highlights the distinct fog frequency and dominant mechanisms along the different trans‐Arctic shipping routes, thereby establishing observed reference for the model validation of simulating Arctic sea fog.

ПОВТОРЯЕМОСТЬ АДВЕКТИВНО-РАДИАЦИОННЫХ ТУМАНОВ НАД АПШЕРОНСКИМ ПОЛУОСТРОВОМ (АЗЕРБАЙДЖАН)

The article examines the physical and meteorological characteristics of advective-radiation fogs formed on the Apsheron Peninsula and nearby islands, including the dependence of atmospheric elements that influence the formation of fogs on the meteorological visibility range, monthly and long-term fog trends. For this purpose, the initial data of aviation meteorological stations in the water area for 1999...2022 were used. The absence of a large morphometric unit on the Apsheron Peninsula and the archipelago, surroundings by the sea, and air masses affecting the area throughout the year determine its synoptic conditions. With the help of physical-meteorological and mathematical-statistical analyses, it has been established that the bulk of advective-radiation fogs formed in the Apsheron waters are repeated in march...april. With this type of fog, it has been established that the range of meteorological visibility varies depending on wind speed and sky conditions. During the period of advective-radiation fogs, south-eastern winds are most often observed in the water area. Analyzes show that an increase in average monthly and annual air temperatures on the peninsula has recently affected the frequency of advective-radiation fogs. Studying the spatiotemporal distributions of fogs can create conditions for the effective organization of aviation work.

Does the Frequency of Fog Affect the Structural Properties of Fagus orientalis in the Hyrcanian Forest?

Does the Frequency of Fog Affect the Structural Properties of Fagus orientalis in the Hyrcanian Forest?

Understanding inland fog and dew dynamics for assessing potential non-rainfall water use in the Atacama

In (semi-)arid regions, harvesting fog and dew can become a complementary solution to traditional water supply. In the Atacama region, a territory of key and water-dependent economic activities, both fog and dew are driven by the advection of marine moisture from the Pacific. Still, little is described regarding the dynamics and water potential of these events. In this study, we analyze the spatiotemporal variability of fog and dew in the Atacama Desert to assess the potential of non-rainfall atmospheric water harvesting. Our research strategy combines three methods to achieve a comprehensive understanding of these phenomena: a satellite-spatial analysis of fog and low cloud frequencies; a thermodynamic characterization of the fog cloud vertical structure; and an observational analysis of fog and dew water collection. Our findings reveal that fog is a regular phenomenon in the area, occurring from 3% to 20% of the year. We estimate that fog cloud reaches 50 km inland and up to ∼1100 m ASL, covering a vast territory where it can be harvested. Fog and dew represent 72% and 28% of the total collected atmospheric water (∼0.2 L m−2 day−1). Both fog and dew represent a complementary natural water source with multiple uses for local industries.

Fog Water: A General Review of Its Physical and Chemical Aspects

Studies concerning fog water have been rapidly increasing due to its negative impacts on different environmental processes. However, fog water harvesting has become beneficial in various countries to overcome water scarcity. Accurate fog forecasting remains a challenging issue due to its spatio-temporal variability and uncertainties despite the development and efforts made to understand its chemistry and microphysics. The literature proved that the decrease in fog frequency over time in most countries is mainly attributed to the improvement in air quality or the change in regional climatic conditions. The current fog review summarizes its different types and collectors, life cycle, and impacts, the effects of aerosols, and the latest results concerning its forecast challenges and frequency. It also highlights the major chemical processes along with the main field studies performed on fog water. The aim of this work is not to provide a criticism about fog but to present a general comprehensive review of its physical and chemical aspects covering up to 330 research and review papers aimed to serve as a basis for new challenges and findings about fog water.

A climatology of Arctic fog along the coast of East Greenland

AbstractThis study presents a comprehensive climatology of coastal fog from four synoptic weather stations operated by the Danish Meteorological Institute along the entire East Greenland coast between 1958 and 2016. Elements investigated include fog frequency, daily timing, temperature, wind, visibility and radiosonde profiles during fog. The spatiotemporal patterns in fog from the low‐ to high‐Arctic locations were related to varying regional seasonal temperatures, surface and upper‐air wind and sea ice conditions, and to correlations with the North Atlantic Oscillation (NAO) and the Greenland Blocking Index (GBI). Results indicate that ˜70–80% of East Greenland fog occurs in summer (MJJA), and yearly fog onset is near‐coincident with the start of sea ice break‐up. This warm‐season fog has the typical characteristics of advection fog, as shown in the radiosonde profiles and the association with a gentle sea breeze. More than 95% of warm‐season fog is warmer than −10°C, and peaks close to 0°C and, therefore, consists of liquid or supercooled water droplets. In the cold season, mixed‐phase fog prevails in the high‐Arctic locations, accounting for ˜70% of observations. Ice fog (T < −30°C) occurs in only 2% of observations and is limited to Northeast Greenland during the cold season. The cold‐season composite radiosonde fog profiles in the high‐Arctic locations are characterized by deep (˜1000 m) and strong (˜6°C) surface‐based temperature inversions. Visibility during most fog conditions is lowest during the warm season (<500 m) and highest during the cold season (<800 m). In Northeast Greenland, visibility during warm‐season fog has decreased by ˜50 m·dec−1 between 1981 and 2016. In Southeast Greenland, fog visibility is high during low GBI and a positive phase of NAO, but no other correlations with climate indices were found.

Impacts of Arctic Sea Fog on the Change of Route Planning and Navigational Efficiency in the Northeast Passage during the First Two Decades of the 21st Century

Under the background of climate change, the Northeast Passage’s navigability is on the rise. Arctic sea fog significantly influences navigational efficiency in this region. Existing research primarily focuses on routes accumulating the lowest distance, neglecting routes with the lowest time and sea fog’s influence on route planning and navigational efficiency. This study compares the fastest and shortest routes and analyzes Arctic sea fog’s impact on the Northeast Passage from June to September (2001–2020). The results show that coastal areas are covered with less sea ice under notable monthly variations. Sea fog frequency is highest near coasts, declining with latitude. September offers optimal navigation conditions due to minimal ice and fog. When only sea ice is considered, the fastest route is approximately 4 days quicker than the shortest. The shortest route has migrated towards the higher latitude over two decades, while the fastest route remains closer to the Russian coast. Adding the impact of sea fog on the fastest route, the speed decreased by 30.2%, increasing sailing time to 45.1%. The new fastest route considering both sea ice and sea fog achieved a 13.9% increase in sailing speed and an 11.5% reduction in sailing time compared to the original fastest route.

Performance of Decision-Tree-Based Ensemble Classifiers in Predicting Fog Frequency in Ungauged Areas

Abstract Fog is a phenomenon that exerts significant impacts on transportation, aviation, air quality, agriculture, and even water resources. While data-driven machine learning algorithms have shown promising performance in capturing nonlinear fog events at point locations, their applicability to different areas and time periods is questionable. This study addresses this issue by examining five decision-tree-based classifiers in a South Korean region, where diverse fog formation mechanisms are at play. The five machine learning algorithms were trained at point locations and tested with other point locations for time periods independent of the training processes. Using the ensemble classifiers and high-resolution atmospheric reanalysis data, we also attempted to establish fog occurrence maps in a regional area. Results showed that machine learning models trained on the local datasets exhibited superior performance in mountainous areas, where radiative cooling predominantly contributes to fog formation, compared to inland and coastal regions. As the fog generation mechanisms diversified, the tree-based ensemble models appeared to encounter challenges in delineating their decision boundaries. When they were trained with the reanalysis data, their predictive skills were significantly decreased, resulting in high false alarm rates. This prompted the need for postprocessing techniques to rectify overestimated fog frequency. While postprocessing may ameliorate overestimation, caution is needed to interpret the resultant fog frequency estimates, especially in regions with more diverse fog generation mechanisms. The spatial upscaling of machine learning–based fog prediction models poses challenges owing to the intricate interplay of various fog formation mechanisms, data imbalances, and potential inaccuracies in reanalysis data.

Analysis of Spatio-Temporal intensity of Sea Fog in Yellow Sea Using Visibility Data of Ocean Research Stations (ORS) and Baengnyeongdo

While existing research on sea fog primarily relied on collecting data from ground observations in coastal areas, this study utilized municipal data from three Korea Ocean Research Stations (KORS) located in the Yellow Sea and Baengnyeongdo. The main objective was to analyze the strength of sea fog in specific locations within the Yellow Sea. The study employed the corrective distance as a measure of intensity and examined variations in sea fog strength according to the monthly and by time period of the study area. The research periods for each research station were as follows: Socheongcho Ocean Research Stations (SORS) from 2014 to 2022, Gageocho Ocean Research Stations (GORS) from 2014 to 2020, Ieodo Ocean Research Stations (IORS) from 2010 to 2015, and Baengnyeongdo from 2016 to 2022. In terms of season, the highest sea fog frequency in SORS and GORS were at 59% and 75% in spring, respectively. While in IORS, sea fog intensively occurred throughout the spring (46%) and summer (47%) seasons. On the other hand, in Baengnyeongdo, the sea fog frequency in summer, spring, autumn and winter were 41%, 25%, 17% and 17%, respectively. Between September and February the occurrence frequency was 19%, 8.1% and 7.3% in SORS, GORS and IORS, respectively which tends to decrease as it descends South of the Yellow Sea. In SORS, sea fog frequency with 0.2 km (strength 2) visibility was 49% while in the case of GORS and IORS it was 15% and 22%, respectively. Besides, the frequency of sea fog which visibility was between 0.2 and 0.5 km (strength 1) was 59% and 56% in GORS and IORS, respectively. In terms of frequency by time period, SORS and GORS showed a normalization maximum of 01 at 01:00 KST where IORS showed 02. Sea fog was not seen at 12:00 in SORS, at 13-17:00 in GORS and at 19-20:00 in IORS. In the future, we will analyze the spatial distribution of sea fog occurring in the Yellow Sea after sea fog verification using satellite images.

Adapting to a Foggy Future Along Trans‐Arctic Shipping Routes

AbstractRapid retreat of Arctic sea ice extends the area of open ocean for new trans‐Arctic shipping routes. However, the projected routes may be too optimistic in terms of savings in shipping costs from shortened trans‐Arctic distances as they do not consider the increased sea fog frequency (SFF) over areas of the retreating sea ice. We show that delays due to sea fog can be 1–4 days, about 23%–27% along the Northwest Passage and 4%–11% along the Northern Sea Route than previous estimated. We design a route based on the projected sea‐ice extent and SFF. The new route can reduce the sailing time by 0.3–1 day by detouring the routes with lighter impacts of sea fog. More importantly the new route will lower the risk of catastrophic accidents compared to the shortest route and saves the additional costs due to unscheduled port calls.

Four decades of aviation visibility at Bhairahawa airport, gateway to Buddha's birthplace Lumbini, Nepal

Over four decades of visibility data at Bhairahawa airport (BWA), a recently upgraded international airport near Lumbini, a UNESCO heritage site in Nepal has been analyzed. In this study, we also investigated one of the important microclimatic behavior of fog i.e., onset and dispersal timings, and its implication on aviation. Temporal variations of poor visibility conditions at BWA are found to be primarily associated with variations in haze and fog. Haze at BWA accounts for the highest percentage (∼27%) of time and its annual occurrence is increasing (0.57% yr−1). There is a significant upward trend of hazy days in all seasons, the highest (1.46% day yr−1) being in post-monsoon. The overall seasonal poor visibility, too, has increased significantly in all seasons, with the highest trend in post-monsoon (1.57% yr−1). Similarly, fog frequency in the winter season has also increased noticeably for fog days (1.05% day yr−1), dense fog days (0.51% day yr−1), general fog hours (0.55% hour yr−1) and dense fog hours (0.20% hour yr−1). We found that fog at BWA is usually formed overnight and dissipates before noon. Daytime onset and late dispersion of fog are more common in the peak winter months of December and January. Further, we investigated the relationship between visibility and aerosol optical depth (AOD) and found a moderate negative correlation (r = − 0.66, p < 0.001) between them in the monsoon season. However, AOD is found to have a weaker correlation with visibility during winter (r = −0.36) and pre-monsoon (r = −0.23) seasons, when there is a more pronounced influence of meteorological conditions on the occurrence of visibility. We have observed a better correlation (r = −0.74) between fine particulate matter concentration (PM2.5) and visibility. Examining the effect of relative humidity (RH) on AOD (or, PM2.5) and visibility revealed that higher RH tends to lower visibility. Visibility at BWA airport is gradually worsening due to local and regional air pollution emissions and changing meteorological conditions. The degraded visibility at BWA airport will negatively impact flight safety and timeliness. Effective implementation of regionally coordinated air pollution mitigation measures can be a sustainable step towards the improvement of visibility in long run. However, the installation of ground equipment like CAT-II/III Instrument Landing System (ILS) for aircraft take-off and landings, and advanced surface movement guidance and control system (A-SMGCS) are highly advisable to lessen the damage potential to aviation.

Long term trends of dry and wet deposition of air pollutants at declining forest site of Mt. Oyama in Japan during 1994–2019

Forest decline, which occurs in mountainous regions in many countries, may result from the effects of acid fog, ozone, or deposition of other pollutants. We observed wet deposition of air pollutants at different altitudes on Mt. Oyama, situated southwest of Tokyo, for 1994 until 2019. During this period, the domestic atmospheric environment was improved in Japan. The average concentration of air pollutants around all the sampling sites on Mt. Oyama decreased by 63.01%, 32.08%, 8.80%, and 39.73% for NH3, HCl, HNO3, and SO2, respectively. The volume weighted mean (VWM) pH values showed an increasing trend for bulk deposition (+0.70% y-1), fog water (+2.58% y-1), and throughfall (+2.60% y-1). Stemflow also increased (cedar, +1.17% y-1; fir, +0.82% y-1), although it included organic acids dissolved from the stem and it primarily had a low VWM pH value. The overall pH value of the fog water increased at the site, although acidic fog was still observed. Comparing fog water between winter and summer, a significant increase in pH occurred in summer, whereas no change occurred in winter. In summer, the sources of pollutants at Mt. Oyama are mainly from mainland Japan, and the frequency of low-pH acidic fog decreased annually. In winter, Mt. Oyama was affected by transboundary pollution, and acid fog occasionally occurred. Improvements in the domestic atmospheric environment and control of transboundary pollution will provide better conditions for mountain ecology that are free from acidic pollutants.

Summer Marine Fog Distribution in the Chukchi–Beaufort Seas

AbstractWe study the spatial and temporal variability of summer marine fog in the Chukchi–Beaufort region (175°E−150°W, 70°–86°N) using the in‐situ visibility measurements aboard the Chinese research fleet Xuelong (I and II) and a fog product we derive using the Vertical Feature Mask product of the spaceborne Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations. The Xuelong in‐situ observations show that the fog frequency in the Chukchi–Beaufort region has a maximum of ∼18% in the early morning and is less than 10% in the rest of the day. The latitudinal distribution of the Xuelong‐based in‐situ fog frequency further shows high fog occurrences at 74°N and 79°N, which are related to the local high fog occurrences near 72°–74°N and 76°–80°N in the central Chukchi–Beaufort region, as revealed by the longitude‐latitude pattern of the CALIPSO‐based spaceborne fog frequency distribution. The CALIPSO‐based fog frequency is also shown to be lower along the continental coastlines than in the Chukchi–Beaufort region. This longitude‐latitude distribution may be explained by a reduced fog formation due to the Pacific warm current flowing into the Arctic region through the Bering Strait in the summer as well as an enhanced fog formation in the Chukchi–Beaufort region when the southward flow of the Beaufort Gyre interacts with the Pacific warm current.

Климатология туманов в Центральном Предкавказье

Introduction. Fog is one of the dangerous weather phenomena, since it has a negative impact on the operation of all types of transport, worsens the ecological state of the air basin of cities, leads to deterioration in the well-being of people with a number of diseases, etc. Therefore, the study of the fog regime and its dynamics is an important task, especially in the era of rapid and significant climate change. The work is devoted to the study of the regime of fogs in various landscapes of the Central Ciscaucasia. The main characteristics of the fog regime in the current climate are calculated. To determine the change in the fog regime, the new century data are compared with data for two multi-year periods of the 20th century. Particular attention is paid to the modern regime of fogs in the resort of Kislovodsk and in airport areas in Mineralnye Vody and Stavropol. Materials and research methods. The information base for the analysis of the fog regime was the observation data of 16 meteorological stations of the Stavropol Krai for 2001–2020, data from the USSR Climate Reference Book [24] and the monograph “Stavropol Territory: modern climatic conditions” [5]. The studies were carried out by methods of physical-statistical and regression analysis. Research results and their discussion. For all meteorological stations of the Central Ciscaucasia, the averaged main characteristics of the fog regime for the first two full 10 years of the new century are calculated: the annual, seasonal and monthly number of days with fog and their total duration in the indicated periods. The extreme values of the specified characteristics are determined. The analysis of the annual course of the main characteristics of fogs has been carried out. Based on the results of a comparative analysis of the obtained data with data over two long-term periods of the 20th century, the characteristic of the dominant trend in long-term changes in the frequency and duration of fogs is given. Conclusion. It is shown that the distribution of fogs over the territory of the Stavropol Krai has a complex character; there is no clear connection with the landscape structure. For most of the region, there is a certain similarity in the trends in changing the fog regime: decrease in the annual number of days with fog; reduction of the total annual duration of fogs; decrease in the proportion of fogs of the cold period in the annual number of days with fog; reduction in the share of fogs of the cold period in the total annual duration of fogs; decrease in the duration of one fog both on average per year and during the cold period.

Rangewide climatic sensitivities and non-timber values of tall Sequoia sempervirens forests

Heavily exploited for its reddish, decay-resistant heartwood, the tallest conifer, Sequoia sempervirens, is a major component of coastal forests from extreme southwestern Oregon to California’s Santa Lucia Mountains. Primary Sequoia forests are now restricted to < 5 % of their former distribution, and mature secondary forests with trees over 60 m tall are even scarcer due to repeated logging. Leveraging allometric equations recently derived from intensive work in both forest types, we climbed, measured, and core-sampled 235 trees in 45 locations distributed across the species range to examine growth trends and understand how tall Sequoia are responding to recent environmental changes. Paired samples of sapwood and heartwood collected along the height gradient were used to quantify Sequoia investment in decay resistance. During the 20th century, trees in most locations began producing more wood than expected for their size with this growth surge becoming pronounced after 1970 and ending around 2000. Radial increments—ring widths—correlate with climatic variables related to water availability, and these relationships are strengthening as temperatures rise. Sensitivity to drought increased from north to south along a 6° latitudinal gradient of decreasing precipitation and summer fog frequency. Sequoia trees north of 40° were least sensitive to drought, producing similar biomass annually during dry and wet years, whereas trees farther south produced less biomass during individual drought years. Hotter 21st century drought barely affected Sequoia growth efficiency (biomass increment per unit leaf mass) north of 40° until the fourth consecutive year (2015), when growth efficiency dropped precipitously, recovering within two years. South of 40°, Sequoia trees exhibited steadily declining growth efficiency during the multi-year drought followed by recovery, but recovery did not occur south of 37° despite ample precipitation in 2017. Sequoia growth efficiency is currently highest in secondary forests north of 40°, where trees produce relatively small amounts of heartwood with the lowest decay resistance (least fungicide) while receiving the most nocturnal summer fog. Increasing sink limitations, whereby rising temperatures, drier air at night, and extreme tree height collectively lower turgor pressure to inhibit cambial activity, may reduce Sequoia growth efficiency while contributing to more durable biomass production. Heartwood and fungicide increments are higher in primary than secondary forests across the species range. Crown structural complexity promotes development of vascular epiphytes and arboreal soil habitats in Sequoia forests with sufficient moisture availability. These habitats are lacking in secondary forests and rare in primary forests south of 40°. After logging, restoration of tall Sequoia forests can be achieved via silviculture that maximizes height increments during early stand development and then retains some dominant trees in perpetuity, allowing them to gain full stature, produce increasingly decay-resistant heartwood, and support significant arboreal biodiversity.

Accounting for non-rainfall moisture and temperature improves litter decay model performance in a fog-dominated dryland system

Abstract. Historically, ecosystem models have treated rainfall as the primary moisture source driving litter decomposition. In many arid and semi-arid lands, however, non-rainfall moisture (fog, dew, and water vapor) plays a more important role in supporting microbial activity and carbon turnover. To date though, we lack a robust approach for modeling the role of non-rainfall moisture in litter decomposition. We developed a series of simple litter decay models with different moisture sensitivity and temperature sensitivity functions to explicitly represent the role of non-rainfall moisture in the litter decay process. To evaluate model performance, we conducted a 30-month litter decomposition study at 6 sites along a fog and dew gradient in the Namib desert, spanning almost an eightfold difference in non-rainfall moisture frequency. Litter decay rates in the field correlated with fog and dew frequencies but not with rainfall. Including either temperature or non-rainfall moisture sensitivity functions improved model performance, but the combination of temperature and moisture sensitivity together provided more realistic estimates of litter decomposition than relying on either alone. Model performance was similar regardless of whether we used continuous moisture sensitivity functions based on relative humidity or a simple binary function based on the presence of moisture, although a Gaussian temperature sensitivity outperformed a monotonically increasing Q10 temperature function. We demonstrate that explicitly modeling non-rainfall moisture and temperature together is necessary to accurately capture litter decay dynamics in a fog-affected dryland system and provide suggestions for how to incorporate non-rainfall moisture into existing Earth system models.