Showing papers in "Earth Interactions in 2021"

The Hazards Posed by Mesoscale Lightning Megaflashes

Abstract: Lightning megaflashes extending over >100-km distances have been observed by the Geostationary Lightning Mappers (GLMs) on NOAA’s R-series Geostationary Operational Environmental Satellites (GOES). The hazards posed by megaflashes are unclear, however, because of limitations in the GLM data. We address these by reprocessing GOES-16 GLM measurements from 1 January 2018 to 15 January 2020 and integrating them with Earth Networks Global Lightning Network (ENGLN) observations. ENGLN verified 194 880 GLM megaflashes as natural lightning. Of these, 127 479 flashes occurred following the October 2018 GLM software update that standardized GLM timing. Reprocessed GLM/ENGLN lightning maps from these postupdate cases provide a comprehensive view of how individual megaflashes evolve. This megaflash dataset is used to generate statistics that describe their hazards. The average megaflash produces 5–7 cloud-to-ground (CG) strokes that are spread across 40%–50% of the flash extent. As flash extent increases beyond 100 km, megaflashes become concentrated in key hot-spot regions in North and South America while the number of CG and intracloud events per flash and the overall peak current increase. CGs in the larger megaflashes occur over 80% of the flash extent measured by GLM, and the majority contain regions where the megaflash is the only lightning activity in the preceding hour. These statistics demonstrate that there is no safe location below an electrified cloud that is producing megaflashes, and current lightning safety guidance is not always sufficient to mitigate megaflash hazards.

Variable impact of COVID-19 lockdown on air quality across 91 Indian cities

Abstract: India responded to the severe acute respiratory syndrome (SARS) coronavirus disease 2019 (COVID-19) pandemic through a three-phase nationwide lockdown: 25 March–14 April, 15 April–3 May, and 4–17 May 2020. We utilized this unique opportunity to assess the impact of restrictions on the air quality of Indian cities. We conducted comprehensive statistical assessments for the air quality index (AQI) and criteria pollutant concentrations for 91 cities during the lockdown phases relative to the preceding seven days (prelockdown phase of 18–24 March 2020) and to corresponding values from the same days of the year in 2019. Both comparisons show statistically significant countrywide mean decrease in AQI (33%), PM2.5 (36%), PM10 (40%), NO2 (58%), O3 (5%), SO2 (25%), NH3 (28%), and CO (60%). These reductions represent a background or the lower bound of air quality burden of industrial and transportation sectors. The northern region was most impacted by the first two phases of the lockdown, whereas the southern region was most affected in the last phase. The northeastern region was least affected, followed by the eastern region, which also showed an increase in O3 during the lockdown. Analysis of satellite-retrieved aerosol optical depth (AOD) shows that effects of restrictions on particulate pollution were variable—locally confined in some areas or having a broader impact in other regions. Anomalous behavior over the eastern region suggests a differing role of regional societal response or meteorological conditions. The study results have policy implications because they provide the observational background values for the industrial and transportation sector’s contribution to urban pollution. © 2021 American Meteorological Society.

Weather Factors Associated with Extremely Large Fires and Fire Growth Days

Abstract: “Megafires” are of scientific interest and concern for fire management, public safety planning, and smoke-related public health management. There is a need to predict them on time scales from days to decades. Understanding is limited, however, of the role of daily weather in determining their extreme size. This study examines differences in the daily weather during these and other, smaller fires, and in the two sets of fires’ responses to daily weather and antecedent atmospheric dryness. Twenty fires of unusual size (over 36 400 ha), were each paired with a nearby large fire (10 100 to 30 300 ha). Antecedent dryness and daily near-surface weather were compared for each set of fires. Growth response to daily weather was also examined for differences between the two sets of fires. Antecedent dryness measured as the Evaporative Demand Drought Index was greater for most of the fires of unusual size than it was for smaller fires. There were small differences in daily weather, with those differences indicating weather less conducive to fire growth for the unusually large fires than the smaller fires. Growth response was similar for the two sets of fires when weather properties were between 40th and 60th percentiles for each fire pair, but the unusually large fires’ growth was observably greater than the smaller fires’ growth for weather properties between the 80th to 100th percentiles. Response differences were greatest for wind speed, and for the Fosberg Fire Weather Index and variants of the Hot-Dry-Windy Index, which combine wind speed with atmospheric moisture.

Cropland Abandonment in the Community-Forestry Landscape in the Middle Hills of Nepal

Abstract: Cropland abandonment has been a major land-use concern, threatening food security globally. Understanding the factors contributing to cropland abandonment advances land-use change science and provides essential information for policy making, both of which aim to improve agriculture land management. Despite many studies conducted on this topic, we still lack in-depth understanding on how feedbacks from the natural system influence cropland-use decisions at the household level in the human system. We fill this knowledge gap by conducting this study in the Middle Hills of Nepal, where community forestry is an integral part of the land-use system. We collected qualitative data through focus-group discussions, key-informant interviews, and review of local community-forest management documents, and we collected quantitative socioeconomic data through a household survey of 415 households. We geolocated 1264 cropland parcels owned by these households and recorded their use statuses. We found that there is an increasing trend of cropland abandonment that is due to multiple socioeconomic, ecological, and biophysical factors. A higher likelihood of cropland abandonment is linked to households that have more out-migrants, female heads, nonagricultural occupation of the household heads, and larger areas of agriculture landholding. The study also found that cropland parcels that are far from the households, close to the forest edge, and on steeper slopes are more likely to be abandoned. These findings provide key information for policy makers to devise effective measures on managing cropland and developing sustainable agriculture in rural Nepal.

Dispersion of Smoke Plumes over South America

Abstract: Satellite and reanalysis products are used to study the atmospheric environment, aerosols, and trace gases in smoke plumes over South America in the period 2000–18. Climatic conditions and fire density maps provide context to link biomass burning across the southern Amazon region (5°–15°S, 50°–70°W) to thick near-surface plumes of trace gases and fine aerosols. Intraseasonal weather patterns that underpin greater fire emissions in the dry season (July–October) are exacerbated by high pressure over a cool eastern Pacific Ocean, for example in September 2007. Smoke-plume dispersion simulated with HYSPLIT reveals a slowing of westward transport between sources in eastern Brazil and the Andes Mountains. During cases of thick smoke plumes over southern Amazon, an upper ridge and sinking motions confine trace gases and fine aerosols below 4 km. Long-term warming, which tends to coincide with the zone of biomass burning, is +0.03°C yr −1 in the air and +0.1°C yr −1 at the land surface. Our study suggests that weather conditions promoting fire emissions also tend to limit dispersion.

Variability in Isolated Convective Activity between Louisville, Kentucky, and Nearby Rural Locations

Abstract: This study analyzes the frequency of strong, isolated convective cells in the vicinity of Louisville, Kentucky. Data from the Severe Weather Data Inventory are used to compare the frequency of convective activity over Louisville with the observed frequency at nearby rural locations from 2003 to 2019. The results show that Louisville experiences significantly more isolated convective activity than do the rural locations. The difference in convective activity between Louisville and the rural locations is strongest during summer, with peak differences occurring between May and August. Relative to the rural locations, Louisville experiences more isolated convective activity in the afternoon and early evening but less activity after midnight and into the early morning. Isolated convective events over Louisville are most likely during quiescent synoptic conditions, whereas rural events are more likely during active synoptic patterns. To determine whether these differences can be attributed primarily to urban effects, two additional cities are shown for comparison—Nashville, Tennessee, and Cincinnati, Ohio. Both Nashville and Cincinnati experience more isolated convective activity than all five of their nearby rural comparison areas, but the results for both are statistically significant at four of the five rural locations. In addition, the analysis of Cincinnati includes a sixth comparison site that overlaps the urbanized area of Columbus, Ohio. For that location, differences in convective activity are not statistically significant.

Is Alaska’s Yukon–Kuskokwim Delta Greening or Browning? Resolving Mixed Signals of Tundra Vegetation Dynamics and Drivers in the Maritime Arctic

Abstract: Alaska’s Yukon–Kuskokwim Delta (YKD) is among the Arctic’s warmest, most biologically productive regions, but regional decline of the normalized difference vegetation index (NDVI) has been a striking feature of spaceborne Advanced High Resolution Radiometer (AVHRR) observations since 1982. This contrast with “greening” prevalent elsewhere in the low Arctic raises questions concerning climatic and biophysical drivers of tundra productivity along maritime–continental gradients. We compared NDVI time series from AVHRR, the Moderate Resolution Imaging Spectroradiometer (MODIS), and Landsat for 2000–19 and identified trend drivers with reference to sea ice and climate datasets, ecosystem and disturbance mapping, field measurements of vegetation, and knowledge exchange with YKD elders. All time series showed increasing maximum NDVI; however, whereas MODIS and Landsat trends were very similar, AVHRR-observed trends were weaker and had dissimilar spatial patterns. The AVHRR and MODIS records for time-integrated NDVI were dramatically different; AVHRR indicated weak declines, whereas MODIS indicated strong increases throughout the YKD. Disagreement largely arose from observations during shoulder seasons, when there is partial snow cover and very high cloud frequency. Nonetheless, both records shared strong correlations with spring sea ice extent and summer warmth. Multiple lines of evidence indicate that, despite frequent disturbances and high interannual variability in spring sea ice and summer warmth, tundra productivity is increasing on the YKD. Although climatic drivers of tundra productivity were similar to more continental parts of the Arctic, our intercomparison highlights sources of uncertainty in maritime areas like the YKD that currently, or soon will, challenge historical concepts of “what is Arctic.”

Spatial Utilization and Microhabitat Selection of the Snow Leopard (Panthera uncia) under Different Livestock Grazing Intensities

Abstract: There is increasing conflict between snow leopards and humans in many protected areas, the main driver of which is the overlap in spatial utilization between snow leopards and livestock. Understanding the spatial utilization and microhabitat selection of snow leopards in areas featuring different levels of livestock grazing is important to better understand and resolve this conflict, but such studies are rare. Here, we conducted line transect and plot surveys in low- and high-grazing-disturbance areas (LGDAs and HGDAs) in Wolong National Reserve, southwestern China. We compared snow leopard spatial utilization and microhabitat characteristics between LGDAs and HGDAs. Results showed that snow leopards had aggregated distribution in both LGDAs and HGDAs, but the distribution of snow leopards in HGDAs was more centralized than in LGDAs. Herb cover and height in LGDAs were greater than in HGDAs. We fit a resource selection function (RSF) that showed that snow leopards preferentially selected higher elevation, smaller basal diameter of shrubs, and lower height of herbs in LGDAs. In contrast, there were no significant microhabitat factors in our snow leopard RSF in HGDAs. Our results indicate that high-intensity grazing tends to reduce the habitat types available to and preferential selectivity of habitat by snow leopards. We recommend that livestock grazing should be controlled to restore the diversity of the alpine ecosystems in Wolong Nature Reserve. Our findings also highlight the need for evaluating the impact of livestock grazing on rare animals in alpine environments (e.g., snow leopard) in other areas facing similar issues.

Simulation of the Water Table Elevation in Shallow Unconfined Aquifers by means of the ERA5 Soil Moisture Dataset: The Umbria Region Case Study

Abstract: This paper concerns the simulation of the water table elevation in shallow unconfined aquifers where infiltration is assumed as the main mechanism of recharge. The main aim is to provide a reliable tool for groundwater management that satisfies water supply managers. Such a tool is a candidate as a physically based alternative to the use of empirical methods or general circulation models. It is based on the use of two widely available sets of data: the water table elevation measurements and soil moisture time series. In fact, the former are usually provided by government agencies on public websites whereas the latter are included in the atmospheric global datasets (reanalysis). It is notable that data from reanalysis are accessible to any citizen and organization around the world on an open-access basis (e.g., Copernicus). In the proposed method, the measured water table elevations are correlated quantitatively with the water fluxes toward the aquifer evaluated using the soil moisture data from ERA5 reanalysis (provided by ECMWF) within a Richards equation–based approach. The analysis is executed using data from the Umbria region (Italy) on both a daily and monthly scale. In fact, these are the time intervals of interest for a proper management of groundwater resources. The proposed relationships include both a logarithmic and linear term and point out the possible different regimes of the shallow aquifers with regard to the recharge due to infiltration. These different mechanisms reflect in the different role played by the water fluxes toward the aquifer in terms of water table elevation changes according to the considered time scale.

Snow-Pit Record from a Coastal Antarctic Site and Its Preservation of Meteorological Features

Abstract: Polar snow pits or ice cores preserve valuable information derived from the atmosphere on past climate and environment changes. A 1.57-m snow-pit record from the coastal site (Styx Glacier) in eastern Antarctica covering the period from January 2011 to January 2015 was discussed and compared with meteorological variables. The dominant contribution of the deposition of sea-salt aerosols due to the proximity of the site to the ocean and processes of sea ice formation was revealed in the ionic concentrations. Consistent seasonal peaks in δ 18 O, δ D, MSA, , and indicate the strong enhancement of their source during warm periods, whereas the sea-salt ions (Na + , K + , Mg 2+ , Ca 2+ , Cl − , and ) exhibit a distinct distribution. Monthly mean δ 18 O positively correlates with the air temperature record from an automatic weather station (AWS) located in the main wind direction. Despite the shortness of the record, we suspect that the slight depletion of the isotopic composition and lowering of the snow accumulation could be related to the cooler air temperature with the decrease of open sea area. Consistency with previous studies and the positive correlation of sea-salt ions in the snow pit indicate the relatively good preservation of snow layers with noticeable climate and environmental signals [e.g., changes in sea ice extent (SIE) or sea surface temperature]. We report a new snow-pit record, which would be comparative and supportive to understand similar signals preserved in deeper ice cores in this location.