Decrease In Surface Albedo Research Articles

Endometabolic profiling of pigmented glacier ice algae: the impact of sample processing

IntroductionGlacier ice algae, mainly Ancylonema alaskanum and Ancylonema nordenskiöldi, bloom on Greenland Ice Sheet bare ice surfaces. They significantly decrease surface albedo due to their purple-brown pigmentation, thus increasing melt. Little is known about their metabolic adaptation and factors controlling algal growth dynamics and pigment formation. A challenge in obtaining such data is the necessity of melting samples, which delays preservation and introduces bias to metabolomic analysis. There is a need to evaluate the physiological response of algae to melting and establish consistent sample processing strategies for metabolomics of ice microbial communities.ObjectivesTo address the impact of sample melting procedure on metabolic characterization and establish a processing and analytical workflow for endometabolic profiling of glacier ice algae.MethodsWe employed untargeted, high-resolution mass spectrometry and tested the effect of sample melt temperature (10, 15, 20 °C) and processing delay (up to 49 h) on the metabolome and lipidome, and complemented this approach with cell counts (FlowCam), photophysiological analysis (PAM) and diversity characterization.Results and ConclusionWe putatively identified 804 metabolites, with glycerolipids, glycerophospholipids and fatty acyls being the most prominent superclasses (> 50% of identified metabolites). Among the polar metabolome, carbohydrates and amino acid-derivatives were the most abundant. We show that 8% of the metabolome is affected by melt duration, with a pronounced decrease in betaine membrane lipids and pigment precursors, and an increase in phospholipids. Controlled fast melting at 10 °C resulted in the highest consistency, and is our recommendation for future supraglacial metabolomics studies.

Observed Energetic Adjustment of the Arctic and Antarctic in a Warming World

Abstract Satellite observations reveal that decreasing surface albedo in both polar regions is increasing the absorption of solar radiation, but the disposition of this absorbed energy is fundamentally different. Fluxes of absorbed solar radiation, emitted thermal radiation, and net energy imbalances are assessed for both polar regions for the last 21 years in the Clouds and Earth’s Radiant Energy System record. Arctic absorbed solar radiation is increasing at 0.98 ± 0.69 W m−2 decade−1, consistent with the anticipated response to sea ice loss. However, Arctic thermal emission is responding at a similar rate of 0.94 ± 0.55 W m−2 decade−1. This is surprising since the radiative impact of ice loss would be expected to favor increasing solar absorption. We find however, that clouds substantially mask trends in Arctic solar absorption relative to clear sky while having only a modest impact on thermal emission trends. As a result, the Arctic net radiation imbalance has not changed over the period. Furthermore, variability of absorbed solar radiation explains two-thirds of the variability in annual thermal emission suggesting that Arctic thermal fluxes rapidly adjust to offset changes in solar absorption and re-establish equilibrium. Conversely, Antarctic thermal emission is not responding to the increasing (although not yet statistically significant) solar absorption of 0.59 ± 0.64 W m−2 decade−1 with less than a third of the annual thermal variability explained by accumulated solar absorption. The Arctic is undergoing rapid adjustment to increasing solar absorption resulting in no change to the net energy deficit, while increasing Antarctic solar absorption represents additional energy input into the Earth system. Significance Statement The polar regions of Earth are undergoing ice loss through ongoing global warming, reducing the ice cover and decreasing solar reflectivity, which would be expected to warm these regions. We use satellite observations to measure the trends in solar absorption and emitted thermal radiation over the Arctic and Antarctic for the last two decades. Arctic thermal emission is increasing at a compensating rate to solar absorption with a close relationship between these processes. Conversely, Antarctic thermal emission is not responding to solar absorption demonstrating that Antarctic surface temperatures are not significantly influenced by the region’s reflectivity. The Arctic is undergoing rapid adjustment to increasing solar absorption through warming, while increasing Antarctic solar absorption represents additional energy input into the Earth system.

Chemistry-albedo feedbacks offset up to a third of forestation's CO2 removal benefits.

Forestation is widely proposed for carbon dioxide (CO2) removal, but its impact on climate through changes to atmospheric composition and surface albedo remains relatively unexplored. We assessed these responses using two Earth system models by comparing a scenario with extensive global forest expansion in suitable regions to other plausible futures. We found that forestation increased aerosol scattering and the greenhouse gases methane and ozone following increased biogenic organic emissions. Additionally, forestation decreased surface albedo, which yielded a positive radiative forcing (i.e., warming). This offset up to a third of the negative forcing from the additional CO2 removal under a 4°C warming scenario. However, when forestation was pursued alongside other strategies that achieve the 2°C Paris Agreement target, the offsetting positive forcing was smaller, highlighting the urgency for simultaneous emission reductions.

Urban aerosol, its radiative and temperature response in comparison with urban canopy effects in megacity based on COSMO-ART modeling

The study of urban aerosol and its influence on radiation and meteorological regime is important due to the climate effect. Using COSMO-ART model with TERRA_URB parameterization, we estimated aerosols and their radiative and temperature response at different emission levels in Moscow. Mean urban aerosol optical depth (AOD) was about 0.029 comprising 20–30% of the total AOD. Urban black carbon mass concentration and urban PM10 accounted for 86% and 74% of their total amount, respectively. The urban AOD provided negative shortwave effective radiative forcing (ERF) of −0.9 W m−2 at the top of the atmosphere (TOA) for weakly absorbing aerosol and positive ERF for highly absorbing aerosol. Urban canopy effects decreased surface albedo from 19.1% to 16.9%, which resulted in positive shortwave ERF at TOA, while for longwave irradiance negative ERF was observed due to additional emitting of urban heat. Air temperature at 2 m decreased independently on the ERF sign, partially compensating (up to 0.5 °C) for urban heat island effect (1.5 °C) during daytime. Mean radiative atmospheric absorption over the Moscow center in clear sky conditions reaches 4 W m−2 due to urban AOD. The study highlights the role of urban aerosol and its radiative and temperature effects.

Modeling Impacts of Urbanization on Winter Boundary Layer Meteorology and Aerosol Pollution in the Central Liaoning City Cluster, China.

The influence of urbanization on the frequent winter aerosol pollution events in Northeast China is not fully understood. The Weather Research and Forecasting Model with Chemistry (WRF-Chem) coupled with urban canopy (UC) models was used to simulate the impact of urbanization on an aerosol pollution process in the Central Liaoning city cluster (CLCC), China. To investigate the main mechanisms of urban expansion and UC on the winter atmospheric environment and the atmospheric diffusion capacity (ADC) in the CLCC, three simulation cases were designed using land-use datasets from different periods and different UC schemes. A comparative analysis of the simulation results showed that the land-use change (LU) and both LU and UC (LUUC) effects lead to higher surface temperature and lower relative humidity and wind speed in the CLCC by decreasing surface albedo, increasing sensible heat flux, and increasing surface roughness, with a spatial distribution similar to the distribution of LU. The thermal effect leads to an increase in atmospheric instability, an increase in boundary layer height and diffusion coefficient, and an increase in the ADC. The LU and LUUC effects lead to a significant decrease in near-surface PM2.5 concentrations in the CLCC due to changes in meteorological conditions and ADC within the boundary layer. The reduction in surface PM2.5 concentrations due to the LU effect is stronger at night than during daytime, while the LUUC effect leads to a greater reduction in surface PM2.5 concentrations during the day, mainly due to stronger diffusion and dilution caused by the effect of urban turbulence within different levels caused by the more complex UC scheme. In this study, the LU and LUUC effects result in greater thermal than dynamic effects, and both have a negative impact on surface PM2.5 concentrations, but redistribute pollutants from the lower urban troposphere to higher altitudes.

Sensitive temperature changes on the Tibetan Plateau in response to global warming

In recent years, rapid global warming has led to a dramatic cryosphere retreat and caused environmental disasters on the Tibetan Plateau (TP). To better understand the near-surface air temperature variation on the TP in response to global warming in the 21st century, we systematically detected temperature changes on the TP relative to global warming regarding warming time, warming amplitude, and elevation-dependent warming (EDW) using the multi-model ensemble (MME) means of 24 CMIP6 models. The results showed that the warming rate on the TP is 1.3–1.45 times more than that of mean global warming from 2015 to 2100, with the TP having already warmed by 1.5 °C above the pre-industrial levels in 2016/2015 and will warm by 2 °C by 2028/2027 under the Shared Socioeconomic Pathway (SSP) scenarios, SSP2–4.5 and SSP5–8.5. In addition, the warming amplitude on the TP in response to global warming levels of 1.5 and 2 °C would be 1.97 and 2.69 °C under the SSP2–4.5 scenario and 1.94 and 2.68 °C under the SSP5–8.5 scenario. Furthermore, EDW amplifies the warming amplitude at high elevations, mainly because of the decrease in surface albedo. The most sensitive warming amplitude in the cryosphere region, with an elevation of 5–5.5 km, would exceed 2.06, 2.79, 4.29, and 5.73 °C when global warming reaches 1.5, 2, 3, and 4 °C under the SSP5–8.5 scenario. This additional 0.56–1.73 °C warming in the high elevation relative to the global mean will intensify the cryosphere ablation on the TP. Thus, considering the projected larger warming trend and amplitude, the high-elevation region on the TP would be particularly sensitive and vulnerable, which is unfavorable for the TP from the perspective of the Paris Agreement warming target.

Deforestation and Its Effect on Surface Albedo and Weather Patterns

Deforestation is an important environmental problem and a key promoter of regional climate change through modifying the surface albedo. The objective of this research was to characterize the impact of deforestation and land use changes on surface albedo (α) and climate patterns in a tropical highland region of Mexico, between the years 2014 and 2021. The main land cover types are coniferous forests (CF), oak and gallery woodlands (OGW), and annual agriculture (AA), which represent more than 88% of the regional territory. We used 2014 and 2021 Landsat 8 OLI images with topographic and atmospheric correction in order to develop an inventory of albedo values for each land cover type in both time scenarios. Albedo images were generated by using the equation proposed by Liang in 2001, which is based on the reflectance of the bands 2, 3, 4, 5, and 7. Differences in albedo values were calculated between the years 2014 and 2021, and those differences were correlated with variations in climate parameters, for which we used climate data derived from the WRF model. In addition, the different land use changes found were classified in terms of triggers for increasing or decreasing surface albedo. We used the Mann–Whitney U Test to compare the 2021 − 2014 climatic deviations in two samples: Sample A, which included sites without albedo change in 2021; and Sample B, including sites with albedo change in 2021. Results showed that between 2014 and 2021, at least 38 events of land use change or deforestation occurred, with albedo increments between 1 and 11%, which triggered an average increment of 2.16% (p < 0.01; Mann–Whitney U Test) of the regional surface albedo in comparison to the 2014 scenario. In this period, the albedo for CF, OGW, and AA also increased significantly (p < 0.001; Mann–Whitney U Test) by +79, +12, and +9%, respectively. In addition, the regional albedo increment was found to be significant and negatively correlated (p < 0.01 Spearman’s coefficient) with relative humidity (RH), maximum temperature (Tmax), and minimum temperature (Tmin), and correlated (p < 0.01) positively with diurnal temperature range (DTR). The Mann–Whitney U Test revealed that 2021 climatic variations in Sample B sites are statistically different (p < 0.05) to 2021 climatic variations in Sample A sites, which demonstrates that albedo changes are linked to a decrease in minimum temperature and relative humidity and an increase in DTR. Conversion of CF and OGW into AA, perennial agriculture (PA), or grassland (GR) always yielded an albedo increment, whilst the conversion of AA to irrigation agriculture (IA) or PA triggered a decrease in albedo, and finally, the pass from GR or AA to protected agriculture (PA) caused albedo to increase or decrease, depending on the greenhouse covers materials. Reducing deforestation of CF and OGW, conversion of AA or GR into PA, and selecting adequate greenhouse covers could help to mitigate regional climate change.

Tropical surface temperature response to vegetation cover changes and the role of drylands.

Vegetation cover creates competing effects on land surface temperature: it typically cools through enhancing energy dissipation and warms via decreasing surface albedo. Global vegetation has been previously found to overall net cool land surfaces with cooling contributions from temperate and tropical vegetation and warming contributions from boreal vegetation. Recent studies suggest that dryland vegetation across the tropics strongly contributes to this global net cooling feedback. However, observation-based vegetation-temperature interaction studies have been limited in the tropics, especially in their widespread drylands. Theoretical considerations also call into question the ability of dryland vegetation to strongly cool the surface under low water availability. Here, we use satellite observations to investigate how tropical vegetation cover influences the surface energy balance. We find that while increased vegetation cover would impart net cooling feedbacks across the tropics, net vegetal cooling effects are subdued in drylands. Using observations, we determine that dryland plants have less ability to cool the surface due to their cooling pathways being reduced by aridity, overall less efficient dissipation of turbulent energy, and their tendency to strongly increase solar radiation absorption. As a result, while proportional greening across the tropics would create an overall biophysical cooling feedback, dryland tropical vegetation reduces the overall tropical surface cooling magnitude by at least 14%, instead of enhancing cooling as suggested by previous global studies.

Irrigation and warming drive the decreases in surface albedo over High Mountain Asia

Human and climate induced land surface changes resulting from irrigation, snow cover decreases, and greening impact the surface albedo over High Mountain Asia (HMA). Here we use a partial information decomposition approach and remote sensing data to quantify the effects of the changes in leaf area index, soil moisture, and snow cover on the surface albedo in HMA, home to over a billion people, from 2003 to 2020. The study establishes strong evidence of anthropogenic agricultural water use over irrigated lands (e.g., Ganges–Brahmaputra) which causes the highest surface albedo decreases (≤ 1%/year). Greening and decreased snow cover from warming also drive changes in visible and near-infrared surface albedo in different areas of HMA. The significant role of irrigation and greening in influencing albedo suggests the potential of a positive feedback cycle where albedo decreases lead to increased evaporative demand and increased stress on water resources.

The impact of climate oscillations on the surface energy budget over the Greenland Ice Sheet in a changing climate

Abstract. Climate change is particularly strong in Greenland, primarily as a result of changes in the transport of heat and moisture from lower latitudes. The atmospheric structures involved influence the surface mass balance (SMB) of the Greenland Ice Sheet (GrIS), and their patterns are largely explained by climate oscillations, which describe the internal climate variability. By using k-means clustering, we name the combination of the Greenland Blocking Index, the North Atlantic Oscillation index and the vertically integrated water vapor as NAG (North Atlantic influence on Greenland) with the optimal solution of three clusters (positive, neutral and negative phase). With the support of a polar-adapted regional climate model, typical climate features marked under certain NAG phases are inter-seasonally and regionally analyzed in order to assess the impact of large-scale systems from the North Atlantic on the surface energy budget (SEB) components over the GrIS. Given the pronounced summer mass loss in recent decades (1991–2020), we investigate spatio-temporal changes in SEB components within NAG phases in comparison to the reference period 1959–1990. We report significant atmospheric warming and moistening across all NAG phases. The pronounced atmospheric warming in conjunction with the increase in tropospheric water vapor enhance incoming longwave radiation and thus contribute to surface warming. Surface warming is most evident in winter, although its magnitude and spatial extent depend on the NAG phase. In summer, increases in net shortwave radiation are mainly connected to blocking systems (+ NAG), and their drivers are regionally different. In the southern part of Greenland, the atmosphere has become optically thinner due to the decrease in water vapor, thus allowing more incoming shortwave radiation to reach the surface. However, we find evidence that, in the southern regions, changes in net longwave radiation balance changes in net shortwave radiation, suggesting that the turbulent fluxes control the recent SEB changes. In contrast to South Greenland under + NAG, the moistening of North Greenland has contributed to decreases in surface albedo and has enhanced solar radiation absorption. Regardless of the NAG phase, increases in multiple atmospheric variables (e.g., integrated water vapor and net longwave radiation) are found across the northern parts of Greenland, suggesting that atmospheric drivers beyond heat and moisture originated from the North Atlantic. Especially in the northern ablation zone, sensible heat flux has significantly increased in summer due to larger vertical and horizontal temperature gradients combined with stronger near-surface winds. We attribute the near-surface wind intensification to the emerging open-water feedback, whereby surface pressure gradients between the ice/snow-covered surface and adjacent open seas are intensified.

Decreasing surface albedo signifies a growing importance of clouds for Greenland Ice Sheet meltwater production

Clouds regulate the Greenland Ice Sheet’s surface energy balance through the competing effects of shortwave radiation shading and longwave radiation trapping. However, the relative importance of these effects within Greenland’s narrow ablation zone, where nearly all meltwater runoff is produced, remains poorly quantified. Here we use machine learning to merge MODIS, CloudSat, and CALIPSO satellite observations to produce a high-resolution cloud radiative effect product. For the period 2003–2020, we find that a 1% change in cloudiness has little effect (±0.16 W m−2) on summer net radiative fluxes in the ablation zone because the warming and cooling effects of clouds compensate. However, by 2100 (SSP5-8.5 scenario), radiative fluxes in the ablation zone will become more than twice as sensitive (±0.39 W m−2) to changes in cloudiness due to reduced surface albedo. Accurate representation of clouds will therefore become increasingly important for forecasting the Greenland Ice Sheet’s contribution to global sea-level rise.

Pan-Alpine glacier phenology reveals lowering albedo and increase in ablation season length

Glaciers in many parts of the world are reported to be undergoing a darkening process (decrease in surface albedo). This has multiple causes, including the presence of impurities (such as mineral dust, carbonaceous particles, algae and cryoconite), and debris. Also glacier melt can induce an albedo decrease by initiating a melt-albedo feedback cycle. The extent of this albedo decrease and its spatial variability in different mountain ranges however are poorly known. In this study, we assess albedo changes on a selection of Alpine glaciers (542 glaciers >0.1 km2) by deriving eight albedo metrics from MODIS MOD10A1 satellite observations over a time period of 20 years (2000–2019). Albedo metrics include the start and end of the ablation season and its length, calculated through the selection of a threshold (albedo = 0.4) to separate melting ice from snow. We further calculated the number of ice melt days, integral of the length of the ablation season, minimum annual albedo, mean summer albedo and mean annual albedo. We identified significant trends in all metrics for a large percentage of glacier cells. A negative trend in minimum albedo (−0.06 decade−1 on average) was identified for 56% of glacier cells, and 70% of glaciers; a positive trend in the length of season (+18 days decade−1 on average) was identified for 11% of glacier cells and 19% of glaciers. Changes in minimum albedo occur mostly around the glacier median elevation, while for other metrics (e.g. start and length of season) changes are more frequent at the glacier termini (i.e. below 25th elevation percentile). We further investigated the relationship between the metrics and climate (downscaled ERA5 reanalysis data) and topographic (ALOS AW3D30 DEM) variability; we found that average summer temperature and elevation are the most significant proxies for all metrics (maximum correlation = 0.40 between elevation and minimum albedo) compared to spring temperature and other topographic variables. Finally, we looked at the ability of the albedo metrics to represent annual and summertime glacier mass balance of 31 selected Alpine glaciers in the World Glacier Monitoring Service database, finding significant correlations between minimum and summertime albedo and annual mass balance (R2 = 0.44 for minimum albedo and 0.40 for summertime albedo using all observations). Considering individual glaciers, all showed significant correlations with minimum albedo, and some of them are strongly correlated (e.g. Argentiere: R2 = 0.84, Saint Sorlin R2 = 0.88). Our glacier phenology approach opens new perspectives for the remote sensing of alpine and polar glaciers.

Decreasing surface albedo signifies a growing importance of clouds for Greenland Ice Sheet meltwater production

Decreasing surface albedo signifies a growing importance of clouds for Greenland Ice Sheet meltwater production

Impact of Urbanization on Meteorology and Air Quality in Chengdu, a Basin City of Southwestern China

Rapid urbanization has the potential to fundamentally perturb energy budget and alter urban air quality. While it is clear that urban meteorological parameters are sensitive to urbanization-induced changes in landscapes, a gap exists in our knowledge about how changes in land use and land cover affect the dynamics of urban air quality. Herein, we simulated a severe O3 episode (10–16 July 2017) and a highly polluted PM2.5 episode (25–30 December 2017) and assessed the changes of meteorological phenomenon and evolution of air pollutants induced by urbanization. We found that the urban expansion area (i.e., land use transition from natural to urban surfaces between 2000 and 2017, UEA) has a significant increase in nocturnal 2-m temperature (T2) with maximum values reaching 3 and 4°C in summer and winter, respectively. In contrast, UEA experienced cooling in the daytime with stronger reductions of T2 in winter than in summer. The T2 variability is primarily attributed to the intense thermal inertia and high heat capacity of the urban canopy and the shadowing effect caused by urbanization. Owing to increased surface roughness and decreased surface albedo as well as shadowing effects, the ventilation index (VI) of UEA increased up to 1,200 m2/s in winter while decreased up to 950 m2/s in summer. Changes in meteorological phenomenon alter physical and chemical processes associated with variations in PM2.5 and O3 concentrations. Urbanization leads to enhanced vertical advection process and weakened aerosol production, subsequently causing PM2.5 levels to decrease by 33.2 μg/m3 during the day and 4.6 μg/m3 at night, respectively. Meanwhile, O3 levels increased by 61.4 μg/m3 at 20:00 due to the reduction of horizontal advection induced by urbanization, while O3 concentrations changed insignificantly at other times. This work provides valuable insights into the effects of urbanization on urban meteorology and air quality over typical megacities, which support informed decision-making for urban heat and air pollution mitigation.

The Midlatitude Response to Polar Sea Ice Loss: Idealized Slab-Ocean Aquaplanet Experiments with Thermodynamic Sea Ice

Abstract Slab-ocean aquaplanet simulations with thermodynamic sea ice are used to study the zonally symmetric mechanisms whereby polar sea ice loss impacts the midlatitude atmosphere. Imposed sea ice loss (difference without and with sea ice with historical CO2 concentration) leads to global warming, polar amplified warming, and a weakening of poleward atmospheric energy transport and the midlatitude storm-track intensity. The simulations confirm an energetic mechanism that predicts a weakening of storm-track intensity in response to sea ice loss, given the change of surface albedo and assuming a passive ocean. Namely, sea ice loss increases the absorption of shortwave radiation by the surface (following the decrease of surface albedo), which increases surface turbulent fluxes into the atmosphere thereby weakening poleward atmospheric energy transport. The storm-track intensity weakens because it dominates poleward energy transport. The quantitative prediction underlying the mechanism captures the weakening but underestimates its amplitude. The weakening is also consistent with weaker mean available potential energy (polar amplified warming) and scales with sea ice extent, which is controlled by the slab-ocean depth. The energetic mechanism also operates in response to sea ice loss due to melting (difference of the response to quadrupled CO2 with and without sea ice). Finally, the midlatitude response to sea ice loss in the aquaplanet agrees qualitatively with the response in more complex climate models. Namely, the storm-track intensity weakens and the energetic mechanism operates, but the method used to impose sea ice loss in coupled models impacts the surface response.

Glacier Ice Surface Properties in South‐West Greenland Ice Sheet: First Estimates From PRISMA Imaging Spectroscopy Data

AbstractSnow and ice melt processes on the Greenland Ice Sheet are a key in Earth's energy balance and are acutely sensitive to climate change. Melting dynamics are directly related to a decrease in surface albedo, amongst others caused by the accumulation of light‐absorbing particles (LAPs). Featuring unique spectral patterns, these accumulations can be mapped and quantified by imaging spectroscopy. We present first results for the retrieval of glacier ice properties from the spaceborne PRISMA imaging spectrometer by applying a recently developed simultaneous inversion of atmospheric and surface state using optimal estimation. The image analyzed in this study was acquired over the South‐West margin of the Greenland Ice Sheet in late August 2020. The area is characterized by patterns of both clean and dark ice associated with a high amount of LAPs deposited on the surface. We present retrieval maps and uncertainties for grain size, liquid water, and algae concentration, as well as estimated reflectance spectra for different surface properties. We then show the feasibility of using imaging spectroscopy to interpret multiband sensor data to achieve high accuracy, frequently repeated observations of changing snow and ice conditions. For example, the impurity index calculated from multiband Sentinel‐3 Ocean and Land Colour Instrument measurements is dependent on dust particles, but we show that algae concentration alone can be predicted from this data with less than 20% uncertainty. Our study evidences that present and upcoming orbital imaging spectroscopy missions such as PRISMA, Environmental Mapping and Analysis Program, Copernicus Hyperspectral Imaging Mission, and the Surface Biology and Geology designated observable, can significantly support research of melting ice sheets.

Sea Breeze Geoengineering to Increase Rainfall over the Arabian Red Sea Coastal Plains

Abstract The Red Sea (RS) has a high evaporation rate, exceeding 2 m of water per year. The water vapor is transported from the shorelines by sea breezes as far as 200 km landward. Relative humidity in the vicinity of the RS exceeds 80% in summer. Nevertheless, precipitation is scarce in most of the Arabian RS coastal plain. In this work we use the Weather Research and Forecasting (WRF) regional model to assess how deliberate changes (geoengineering) in the surface albedo or conversion of bare land to wide-leaf forests over a vast coastal plain region affect precipitation over the Arabian RS coast. Our simulations show that geoengineering of land surface characteristics perturbs coastal circulation; alters temperature, moisture, and momentum exchange between the land surface and atmosphere; and changes the breeze intensity, cloud cover, and eventually the amount of precipitation. We find that extended afforestation and increased surface albedo are not effective in triggering rainfall over the RS coastal plains. Conversely, decreasing surface albedo to 0.2, assuming installation of solar panels over the coastal plains, increases surface air temperature by 1–2 K, strengthens horizontal surface temperature differences between sea and land, intensifies breezes, increases water vapor mixing ratio in the boundary layer above 3 km by about 0.5 g kg−1, enhances vertical mixing within the planetary boundary layer, and generates 1.5 Gt of extra rainwater, equivalent to the annual consumption of five million people. Thus, this form of regional land surface geoengineering, along with advanced methods of collection and underground storage of freshwater, provides a feasible solution to mitigation of the existing water crisis in the arid coastal regions.

Effect of land use change on summertime surface temperature, albedo, and evapotranspiration in Las Vegas Valley

Urban surfaces affect the surface energy budget, which plays a defining role in outdoor water requirements changing an area's evapotranspiration. They also affect thermal comfort levels for humans, animals, and vegetation by causing the surface temperature to vary. This study analyzes the effects of land use change on the surface albedo, land surface temperature (LST), and evapotranspiration (ET) of the arid Las Vegas Valley (LVV). The changes in land use considered include transitions from barren and rural surfaces into urban surfaces covered with residential, commercial buildings, roadways, and turf grass. The impacts of these changes were determined by analyzing trends over the summer periods from 1990 to 2017. Remote sensing data acquired by Thematic Mapper (TM) and Operational Land Imager (OLI) aboard Landsat satellite were used to retrieve various geophysical characteristics, including albedo and LST. The ET was estimated using the Mapping of Evapotranspiration using Internal Calibration (METRIC) model with remote sensing input data. The geophysical characteristic trends, in response to urban land use change, were quantified using Mann Kendall's trend analysis.The results showed that commercial buildings and roadways are the main contributors to increased LST. Land use change from rural to commercial buildings decreased surface albedo by 0.4 ± 0.01 with a Sen's slope (S) of 0.001–0.003 units/summer/year, and increased temperature by 7 ± 0.2 K with S = 0.2 and 0.4 K/summer/year. Turf grass removal increased temperatures by 20 ± 0.3 K, while urbanization, in general, increased LST by 5 ± 0.3 K. Roadway surfaces, primarily covered with asphalt, were the main contributors to temperature increase of LST 17 ± 0.1 K and S = 0.2–0.8 K/summer/year, while decreasing albedo by 1 ± 0.01 with S = 0.001–0.003 units/summer/year. Turf grass development maintained LST in the valley throughout the study period, showing significant ET increase (S = 0.04–0.06 mm/summer/year), with an average increase of 1 ± 0.07 mm/day. This study can help water managers and urban planners to understand the role of land use change in irrigation water demand and urban thermal comfort.

A Feasibility Study for Determining the Sensible Heat Flux to and from Small Green Roofs

Eddy covariance is an established technique for registering sensible heat fluxes. However, this method is less adequate for smaller surfaces that cannot match the associated footprint. As an alternative technique, a recently constructed acoustic anemometer (Ly-ATOM) is tested, which operates horizontally at an extension of circa 1 m and a data-acquisition frequency of 1 Hz. The Ly-ATOM device reproduces both the acoustic virtual temperature and the horizontal wind components registered by a three-dimensional sonic anemometer. As this Ly-ATOM device can be applied much closer to the ground compared with a sonic anemometer, the size of the related source area is significantly reduced (by a factor of 25). Two methods are used to retrieve the sensible heat flux from variance characteristics of temperature and the horizontal wind components recorded by the Ly-ATOM device: combining the flux-variance-similarity and alternative-flux-variance methods for use in unstable and stable stratification, respectively, yields good results for the sonic measurements. Therefore, these methods can be applied to the Ly-ATOM device as well. In investigating the sensitivity to detect modified surface characteristics, specifically increased evapotranspiration and decreased surface albedo, the Ly-ATOM device proves to be superior to the sonic anemometer which is more vertically removed from the surface of interest.

Major surface melting over the Ross Ice Shelf part II: Surface energy balance

AbstractThe West Antarctic climate is under the combined impact of synoptic and regional drivers. Regional factors have contributed to more frequent surface melting with a similar pattern recently, which accelerates ice loss and favors global sea‐level rise. Part I of this research identified and quantified the two leading drivers of Ross Ice Shelf (RIS) melting, viz. foehn effect and direct marine air advection, based on Polar WRF (PWRF) simulations. In this article (Part II), the impact of clouds and the pattern of surface energy balance (SEB) during melting are analyzed, as well as the relationship among these three factors. In general, net shortwave radiation dominates the surface melting with a daily mean value above 100 W·m−2. Foehn clearance and decreasing surface albedo respectively increase the downward shortwave radiation and increase the absorbed shortwave radiation, significantly contributing to surface melting in areas such as western Marie Byrd Land. Also, extensive downward longwave radiation caused by low‐level liquid cloud favors the melting expansion over the middle and coastal RIS. With significant moisture transport occurring over more than 40% of the time during the melting period, the impact from net radiation can be amplified. Moreover, frequent foehn cases can enhance the turbulent mixing on the leeside. With a Froude number (Fr) around 1 or slightly larger, fast downdrafts or reversed wind flows can let the warm foehn air penetrate down to the surface with up to 20 W·m−2 in sensible heat flux transfer to the ground. However, when the Froude number is close to infinity with breaking waves on the leeside, the contribution of turbulence to the surface warming is reduced. With better understanding of the regional factors for the surface melting, prediction of the future stability of West Antarctic ice shelves can be improved.