Changes In Surface Albedo Research Articles

Assessing climatic benefits from forestation potential in semi-arid lands

Forestation actions are a major tool for both climate-change mitigation and biodiversity conservation. We address two weaknesses in this approach: the little attention given to the negative effects of reduced albedo associated with forestation in many regions, and ignoring the potential of drylands that account for 40% of the global potential land area for forestation. We propose an approach to identify suitable land for forestation and quantify its ‘net equivalent carbon stock change’ over 80 years of forest lifetime (NESC), accounting for both carbon sequestration and albedo changes. We combined remote-sensing tools with data-based estimates of surface parameters and with published climate matrices, to identify suitable land for forestation actions. We then calculated the cumulative (over 80 years) ‘net sequestration potential’ (ΔSP), the ‘emission equivalent of shortwave radiation forcing’ (EESF) due to changes in surface albedo, and, in turn, the combined NESC = ΔSP−EESF, of planting forests with >40% tree-cover. Demonstrating our approach in a large climatically diverse state (Queensland), we identified 14.5 million hectares of potential forestation land in its semi-arid land and show that accounting for the EESF, reduces the climatic benefits of the ΔSP by almost 50%. Nevertheless, it results in a total NESC of 0.72 Gt C accumulated by the end of the century, and 80 years of forestation cycle. This estimated NESC is equivalent to 15% of the projected carbon emissions for the same period in Queensland, for a scenario of no change in emission rates during that period. Our approach extends restoration efforts by identifying new land for forestation and carbon sequestration but also demonstrates the importance of quantifying the climatic value of forestation in drylands.

Influence of Land Use Change on the Surface Albedo and Climate Change in the Qinling-Daba Mountains

Land use changes affect the surface radiative budget and energy balance by changing the surface albedo, which generates radiative forcing, impacting the regional and global climate. To estimate the effect of land use changes on the surface albedo and climate change in a mountainous area with complex terrain, we obtained MODIS data, identified the spatial–temporal characteristics of the surface albedo caused by land use changes, and then calculated the radiative forcing based on solar radiative data and the surface albedo in the Qinling-Daba mountains from 2000 to 2015. The correlation between the land use changes and the radiative forcing was analyzed to explore the climate effects caused by land use changes on a kilometer-grid scale in the Qinling-Daba mountains. Our results show that the primarily land use changes were a decrease in the cultivated land area and an increase in the construction land area, as well as other conversions between six land use types from 2000 to 2015. The land use changes led to significant changes in the surface albedo. Meanwhile, the radiative forcing caused by the land use had different magnitudes, strengths, and occurrence ranges, resulting in both warming and cooling climate change effects.

An integrated assessment on the warming effects of urbanization and agriculture in highly developed urban agglomerations of China

Urbanization and agriculture, the two major and concurrent land use activities, can dramatically alter land surface temperature (LST) through multiple biophysical processes. However, previous studies mainly focused on the warming effects of urbanization in large cities and/or urban core areas that may greatly underestimate the land use impacts on regional climate. Using natural forest as a reference, we assessed the LST changes of both urbanization and agriculture in the three most developed urban agglomerations of China (Jing-Jin-Ji, JJJ; Yangtze River Delta, YRD; Pearl River Delta, PRD) according to satellite observations. Results show that the urban-dominated lands warm the daytime LST substantially, especially in the south subtropical PRD (with an annual mean intensity of 5.5 °C), and the highest do not occur in the core cities. The crop-dominated lands also warm the daytime LST dramatically, especially in the temperate semi-humid JJJ (with an annual mean intensity of 3.9 °C). The daytime warming effects increase significantly from 2003 to 2018 mainly due to urban expansion in crop-dominated and mixed lands. The two land uses continue to warm the LST at night though in a lower magnitude in the PRD. However, the urban-dominated lands warm the LST slightly and the crop-dominated lands cool the LST substantially at night in the JJJ and YRD. Overall, the crop-dominated and/or mixed lands dominate the regional LST changes owing to their large areas. We further show that the daytime warming effects of the two land uses are likely caused by the changes of evapotranspiration, whereas the nighttime cooling effects might be mainly due to the changes in surface albedo and roughness. Our results highlight the importance of considering the urbanization in small-medium sized satellite cities and the more widespread agricultural activities in rural areas when assessing the regional climate change and formulating the mitigation strategies.

Reconstruction of Historical Land Surface Albedo Changes in China From 850 to 2015 Using Land Use Harmonization Data and Albedo Look‐Up Maps

AbstractLand surface albedo is a critical parameter of the Earth's energy budget and has been greatly altered by climate change and human activities. To improve our understanding of historical land surface albedo changes and their climatic effects before the satellite remote sensing era, we reconstructed land surface albedo in China from 850 to 2015 using the historical land use harmonization version 2 (LUH2) data set and albedo look‐up maps, and estimated the radiative forcing induced by land surface albedo changes using atmospheric radiative kernels. The reconstruction results showed that the annual‐mean land surface albedo in China increased by 0.00110 during 850–2015, and the rate of increase was accelerated by the expansion of croplands during recent centuries. The most significant increases in land surface albedo were found in the Huang‐Huai‐Hai (HHH; +0.00646) and Northeast China (NE; +0.00501), which were primarily driven by anthropogenic land cover transformations (e.g., land reclamation, deforestation, and urbanization) and can be enhanced by the vegetation masking effect on snow cover. The radiative forcing induced by land surface albedo changes in China during 850–2015 and 1750–2015 was −0.09 ± 0.04 and −0.06 ± 0.02 W m−2, respectively, which indicated that the land surface albedo changes produced a slight climate cooling effect, helping to offset the warming effect caused by greenhouse gas emissions.

Croplands intensify regional and global warming according to satellite observations

Croplands, occupying approximately 13% of the Earth's land surface, can dramatically alter surface temperature via multiple biophysical processes. However, it remains unclear whether and to what extent croplands warm or cool the land surface globally. Here we present new evidence of the temperature effects of global croplands based on high-resolution satellite observations of land surface temperature (LST). We find general daytime warming and nighttime cooling of crop-dominated lands (cropland intensity ≥90%) relative to other vegetation cover, with net daily cooling in the arid zone and net daily warming in all other areas. On a per-pixel basis, however, nearly half of the crop-dominated lands cool daytime LST and/or warm nighttime LST. The temperature effects vary greatly by location and season. The per-pixel intensity can exceed 10 °C likely due to the changes in surface evapotranspiration, albedo, and background climate. By extending the LST changes of crop-dominated lands to the full land surface, we find that croplands make large contributions to regional and global land surface warming. Daytime warming can reach 0.56 °C in Europe during spring. Nationally, China, India, and Brazil lead the warming due to their large cropland areas and strong local climate effects. Our results highlight the importance of accounting for the biophysical effects of croplands for projecting climate change and formulating adaptation and mitigation strategies.

CO<sub>2</sub>-equivalence metrics for surface albedo change based on the radiative forcing concept: a critical review

Abstract. Management of Earth's surface albedo is increasingly viewed as an important climate change mitigation strategy both on (Seneviratne et al., 2018) and off (Field et al., 2018; Kravitz et al., 2018) the land. Assessing the impact of a surface albedo change involves employing a measure like radiative forcing (RF) which can be challenging to digest for decision-makers who deal in the currency of CO2-equivalent emissions. As a result, many researchers express albedo change (Δα) RFs in terms of their CO2-equivalent effects, despite the lack of a standard method for doing so, such as there is for emissions of well-mixed greenhouse gases (WMGHGs; e.g., IPCC AR5, Myhre et al., 2013). A major challenge for converting Δα RFs into their CO2-equivalent effects in a manner consistent with current IPCC emission metric approaches stems from the lack of a universal time dependency following the perturbation (perturbation “lifetime”). Here, we review existing methodologies based on the RF concept with the goal of highlighting the context(s) in which the resulting CO2-equivalent metrics may or may not have merit. To our knowledge this is the first review dedicated entirely to the topic since the first CO2-eq. metric for Δα surfaced 20 years ago. We find that, although there are some methods that sufficiently address the time-dependency issue, none address or sufficiently account for the spatial disparity between the climate response to CO2 emissions and Δα – a major critique of Δα metrics based on the RF concept (Jones et al., 2013). We conclude that considerable research efforts are needed to build consensus surrounding the RF “efficacy” of various surface forcing types associated with Δα (e.g., crop change, forest harvest), and the degree to which these are sensitive to the spatial pattern, extent, and magnitude of the underlying surface forcings.

Influence of past vegetation changes on estimates of ground surface temperature histories GSTH obtained by inversion of borehole temperature logs: Example from the Western Canadian Sedimentary Basin

Functional space inversions (FSI) of precise temperature logs from 43 wells, located in low conductivity clastic sediments of the Western Canadian Sedimentary Basin, (WCSB), reveal evidence of extensive, recent ground surface temperature (GST) warming. Simultaneous inversion of log data acquired during the period of 1987-2005, as well as averaging of the individual site reconstructions of subsurface temperature signals, indicate evidence of high magnitude of warming of about 2°C (with standard deviations of 0.7°C). Magnitudes of such warning events exceeds 3-4 times that of globally averaged continental GST’s for the 20th century and is significantly higher than that of changes in surface air temperatures (SAT) based on instrumental records in the WCSB. Within this region, GST warming in the 20th century could have been at least partially caused by changes in vegetation cover. The temporary or permanent removal of vegetation, through deforestation, forest fires, and grassland conversion for agriculture occurred in the relatively young provinces of WCSB, during centennial long settlement and development programs. This might have significantly changed the surface properties of the area, since changes in surface albedo affects the radiation budget, while changes in the thermal, moisture and aerodynamic characteristics affect the energy balance. The results of our modelling for typical range of bedrock thermal diffusivities and assumed surface warming history for studied areas in WCSB show that a possible jump in ground surface temperature can easily be interpreted in the FSI results as a gradual warming event of large amplitude and attributed to SAT.

Minimum levels of atmospheric oxygen from fossil tree roots imply new plant−oxygen feedback

The appearance and subsequent evolution of land plants is among the most important events in the earth system. Plant resulted in a change of earth surface albedo and the hydrological cycle, as well as increased rock weatherability thereby causing a persistent change in atmospheric CO2 and O2. Land plants are, however, themselves dependent on O2 for respiration and long‐term survival, something not considered in current geochemical models. In this perspective, we highlight two aspects of land plants’ dependency on O2 relevant for the geobiological community: (a) fossil root systems can be used as a proxy for minimum levels of past atmospheric O2 consistent with a given fossil root depth; and (b) by identifying a positive feedback mechanism involving atmospheric O2, root intensity, terrestrial primary production and organic carbon burial. As an example, we consider archaeopterid fossil root systems, resembling those of modern mature conifers. Our soil–plant model suggest that atmospheric O2 with 1 SD probably reached pressures of 18.2 ± 1.9 kPa and 16.8 ± 2.1 kPa by the Middle and Late Devonian, respectively, that is 86 ± 9% and 79 ± 10% of the present‐day 21.2 kPa.

Time-series snowmelt detection over the Antarctic using Sentinel-1 SAR images on Google Earth Engine

The Antarctic ice sheet is an important mass of glacier ice. It is particularly sensitive to climate change, and the flow of Antarctica's inland glaciers into the sea, accelerated by collapsing ice shelves, threatens global sea level rise. The amount of snowmelt on the surface of the ice sheet is an important metric for accurately assessing surface material loss and albedo change, which affect the stability of the ice sheet. This study proposes a framework for quickly extracting time-series freeze-thaw information at the continental scale and 40 m resolution by taking advantage of the huge amount of synthetic aperture radar (SAR) data acquired by Sentinel-1 satellites over the Antarctic, available for rapid processing on Google Earth Engine. Co-orbit normalization is used in the proposed framework to establish a unified standard of judgement by reducing the variations in the backscattering coefficient introduced by observation geometry, terrain fluctuations, and melt conditions between images acquired at different times. We implemented the framework to produce a massive dataset of both monthly freeze-thaw information over the Antarctic and higher temporal resolution freeze-thaw information for the Larsen C ice shelf from 2015 to 2019, with overall accuracies of 93% verified by a manual visual interpretation method and 84% evaluated from automatic weather station temperatures. Due to its effectiveness and robustness, the framework can be used to analyse the spatiotemporal distribution of snowmelt, the change in melt area, and anomalous melt events in Antarctica, especially those in Larsen C caused by foehn wind.

Impact of Quasi‐Idealized Future Land Cover Scenarios at High Latitudes in Complex Terrain

AbstractAfforestation is gaining popularity as a climate mitigation policy in many countries, including high latitude regions such as Norway. However, the impacts of afforestation on local‐to‐regional climate is poorly understood. This study uses the Weather Research and Forecasting model to investigate the biogeophysical impacts of different forestry scenarios on the local‐to‐regional climate of Norway. The forestry scenarios considered are the conversion of open spaces to either evergreen forest by active afforestation or to mixed forest by natural succession. Results show both forestry scenarios lead to additional warming of surface temperatures in winter and spring (between 1.0°C and 1.5°C) and cooling in summer (between −1.6°C and −1.3°C). A temperature decomposition analysis shows that the warming in winter and spring is driven by surface albedo changes while summer cooling is driven by changes in sensible heat fluxes for afforestation and surface albedo for natural succession. Maximum 2 m air temperature increases considerably in spring in both forestry scenarios (∼0.8°C to 1.0°C). Analysis of precipitation, multiple climate indices and extremes, reveal little or no response to the different forestry scenarios. The largest societally relevant response to the forestry scenarios is the partial mitigation of the reduction in snow days expected from global warming by 10–20 days. This suggests that implementing current afforestation policies for climate mitigation in Norway may adversely exacerbate some effects of global warming locally while mitigating others. As such, the impacts of afforestation on the local‐to‐regional climate at high latitudes are complex and cannot support or dismiss afforestation as a climate mitigation policy.

Assessment of Optimum Installation and Power Injection Parameters for a Bifacial Rooftop System

Bifacial Photovoltaics has gained significant traction in recent years due to a combination of superior radiation capture capabilities and reducing costs. This study builds on a prior 1.07 MW (DC) solar system analysis for Effat University Campus in Jeddah, Saudi Arabia, by adding a Bifacial system. The paper describes a modeling methodology focusing on critical parameters that affect bifacial gains, such as the solar system's tilt angle, surface albedo, and shading. The results have been summarized as sensitivities to changes in input variables such as the surface albedo with ceteris paribus assumption. This case study showed a change in surface albedo to increase the specific production from 1771 kWh/kW to 1829 kWh/kW suggesting an increase in bifacial gain of more than 3%. https://dorl.net/dor/20.1001.1.13090127.2021.11.2.23.2

Sensitivity of surface albedo derived from METEOSAT data to drought episodes in a semi-arid region (M’Sila, north center of Algeria)

Drought is a natural phenomenon that affects ecological processes, land productivity, and human life. The phenomenon is slow to settle down and its impacts are not instantaneous, requiring an early monitoring of their signs of appearance. In order to track the effect drought on the land surface dynamics by means of surface albedo changes, we intend to exploit the VIS-channel reference image from the METEOSAT satellite data, which is an associated product of the new version of the Infrared Difference Dust Index (IDDI). The surface albedo is retrieved from the calibrated VIS-channel reference radiance, atmospherically corrected by the radiative transfer code 6S (Second Simulation of a Satellite Signal in the Solar Spectrum). In this study, we inspect the sensitivity of monthly surface albedo to drought events over a semi-arid region (M’Sila, center of northern Algeria) during the period covered by three METEOSAT satellites (5, 6, and 7). Two drought indices, SPI (Standardized Precipitation Index) and SPEI (Standardized Precipitation Evapotranspiration Index), were calculated at multiple timescales and were correlated with surface albedo over the study region. The results show that the correlation of surface albedo with the two drought indices at the timescale of 1 month (current month) is not necessarily the best indicator of the installation of a drought event. Additionally, we find that the sensitivity of surface albedo to drought indices at a medium timescales class (average of correlation coefficient at 6, 9, and 12 months), is more sensitive to SPEI index (principally 6-month timescale), during the growing season (April to September). It is also more sensitive to SPI index (principally 12-month timescale), during the supplying and charging period of water resources (October to March).

Biases in the albedo sensitivity to deforestation in CMIP5 models and their impacts on the associated historical radiative forcing

Abstract. Climate model biases in the representation of albedo variations between land cover classes contribute to uncertainties on the climate impact of land cover changes since pre-industrial times, especially on the associated radiative forcing. Recent publications of new observation-based datasets offer opportunities to investigate these biases and their impact on historical surface albedo changes in simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Conducting such an assessment is, however, complicated by the non-availability of albedo values for specific land cover classes in CMIP and the limited number of simulations isolating the land use forcing. In this study, we demonstrate the suitability of a new methodology to extract the albedo of trees and crops–grasses in standard climate model simulations. We then apply it to historical runs from 17 CMIP5 models and compare the obtained results to satellite-derived reference data. This allows us to identify substantial biases in the representation of the albedo of trees and crops–grasses as well as the surface albedo change due to the transition between these two land cover classes in the analysed models. Additionally, we reconstruct the local surface albedo changes induced by historical conversions between trees and crops–grasses for 15 CMIP5 models. This allows us to derive estimates of the albedo-induced radiative forcing from land cover changes since pre-industrial times. We find a multi-model range from 0 to −0.17 W m−2, with a mean value of −0.07 W m−2. Constraining the surface albedo response to transitions between trees and crops–grasses from the models with satellite-derived data leads to a revised multi-model mean estimate of −0.09 W m−2 but an increase in the multi-model range. However, after excluding one model with unrealistic conversion rates from trees to crops–grasses the remaining individual model results vary between −0.03 and −0.11 W m−2. These numbers are at the lower end of the range provided by the IPCC AR5 (-0.15±0.10 W m−2). The approach described in this study can be applied to other model simulations, such as those from CMIP6, especially as the evaluation diagnostic described here has been included in the ESMValTool v2.0.

Plants with less chlorophyll: A global change perspective.

The necessary reduction of greenhouse gas (GHG) emissions may lead in the future to an increase in solar irradiance (solar brightening). Anthropogenic aerosols (and their precursors) that cause solar dimming are in fact often co‐emitted with GHGs. While the reduction of GHG emissions is expected to slow down the ongoing increase in the greenhouse effect, an increased surface irradiance due to reduced atmospheric aerosol load might occur in the most populated areas of the earth. Increased irradiance may lead to air warming, favour the occurrence of heatwaves and increase the evaporative demand of the atmosphere. This is why effective and sustainable solar radiation management strategies to reflect more light back to space should be designed, tested and implemented together with GHG emission mitigation. Here we propose that new plants (crops, orchards and forests) with low‐chlorophyll (Chl) content may provide a realistic, sustainable and relatively simple solution to increase surface reflectance of large geographical areas via changes in surface albedo. This may finally offset all or part of the expected local solar brightening. While high‐Chl content provides substantial competitive advantages to plants growing in their natural environment, new plants with low‐Chl content may be successfully used in agriculture and silviculture and be as productive as the green wildtypes (or even more). The most appropriate strategies to obtain highly productive and highly reflective plants are discussed in this paper and their mitigation potential is examined together with the challenges associated with their introduction in agriculture.

In-situ spectroscopy and shortwave radiometry reveals spatial and temporal variation in the crown-level radiative performance of urban trees

In conventional microclimate environment modelling, and the development of tree planning strategies for urban heat mitigation, tree crown surface albedo for any given species is assumed to be a constant. However, our recent research into urban tree radiative performance at the crown level implied that tree crown surface albedo changes over time. Based on the in-situ spectroscopy protocols established previously to measure tree crown transflectance, variation in the characteristics of tree crown surface albedo was explored combining spectroscopy and solar shortwave radiometry. Three commonly planted native UK tree species, Carpinus betulus, Acer campestre, and Taxus baccata, were sampled. Spatial distribution profiles of tree crown transflectance measured at fixed solar altitudes were normalised by in-situ spectroradiometry. Tree crown transflectance in the near infrared (NIR) region was found to be proportionally linked to tree crown surface albedo. Within each species, mean tree crown transflectance in the NIR region of 800–900 nm was approximately 2.5 times tree crown surface albedo. It was further found that infrared radiation (700–2500 nm) accounted for more than 90% of the total transflected shortwave radiation from tree crowns. The results demonstrate that tree crown surface albedo linearly increases with momentary solar altitude and the maximum tree crown surface albedo corresponds to maximum solar altitude at solar noon on sunny days in summer. Tree crown surface albedo across species tends to be strongly dependent on leaf size if considering visibly dense crown foliage. Our findings provide important insights into tree radiative shading effects resulting from temporal variation in tree crown surface albedo, with consequences for urban microclimate modelling and the development of urban heat mitigation strategies.

Divergent trends of urban thermal environmental characteristics in China

Due to the rapid urbanization in China, urban expansion has gradually shifted from large cities to small cities, causing spatiotemporal changes in the urban thermal environment. The differential thermal environmental characteristics of 334 cities at different hierarchy caused by urbanization are investigated in this study. Then, the spatiotemporal changes of land surface temperature (LST), albedo, and emissivity among urban areas and their surrounding buffer areas are analyzed during 2000–2015. We found that the urban warming effect is usually prominent in the daytime, with an obvious seasonal differentiation between 0.32 °C[0.27,0.38] in summer and -0.14 °C[-0.20,-0.07] in winter. The nighttime warming effect during summer resembles that in winter, in the range 0.23–0.25 °C. In addition, the number of cities with intensifying trends of the warming effect in summer daytime account for 50% of the total cities, but only 9% in winter nighttime, 23% in summer nighttime, and 25% in winter daytime. Large cities usually have obvious warming effects compared with small cities. But the highest warming effect is found in megacities during the daytime and in medium cities during the nighttime. In southern subtropical cities, the warming of urban zones is high in the daytime and low in the nighttime, while it is opposite in arid and semiarid regions, especially in winter. The negative correlations between the difference of surface albedo (emissivity) and LST in megacities and metropolitan areas emphasize that nighttime warming primarily results from radiation absorption and release affected by urbanization. This study may advance the understanding of the heterogeneity in the warming effects of different cities in China and support policy formulation and regulation to adapt to urban warming.

Assessing land degradation induced by recreational activities in the Algodones Dunes, California using MODIS satellite imagery

This research investigated spatial and temporal environmental changes associated with climatic variability and off-highway vehicle (OHV) activity in the Algodones Dunes, California, using time-series analysis of Moderate Resolution Imaging Spectroradiometer imagery from 2001 to 2016. We compared changes in land cover, surface albedo, and surface temperatures between the Imperial Sand Dunes Recreation Area (ISDRA) and areas with no OHV activity in the North Algodones Dunes Wilderness area (NADW). Both areas showed a decreasing normalized difference vegetation index (NDVI) and an increasing albedo from 2001 to 2016; however, ISDRA had a lower NDVI value and higher albedo compared to the adjacent NADW. Transects across these adjoining areas revealed substantial differences in daytime and nighttime land surface temperatures. ISDRA had an appreciably higher mean daytime temperature and a lower mean nighttime temperature compared to those within NADW. Results suggest direct association between increasing OHV activity and reduced vegetation cover, increased soil exposure, and higher daytime temperatures in the Algodones Dunes. We recommend enhanced monitoring of ecosystem and land use changes coupled with enhanced land use management to reduce the contributions of recreational OHV activity on land degradation and to maintain habitat for key species and ecosystems of interest in the dune field.

Influence of two management practices in the Canadian Prairies on radiative forcing

Surface albedo and soil carbon sequestration are influenced by agricultural management practices which impact the Earth's radiation budget and climate change. In this study we investigate the impact of reduced summer fallowing and reduced tillage in the Canadian Prairies on climate change by estimating the change in radiative forcing due to albedo and soil carbon sequestration. Seasonal variations of albedo, which are dependent on agricultural management practices and soil colour in three soil zones, were derived from 10-day composite 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) data. Using this information, we found an overall increase of surface albedo due to the conversion from summer fallowing to continuous cropping and from conventional tillage (CT) to either no-tillage (NT) or reduced tillage (RT). The increase was dependent on soil brightness, type of vegetation and snow cover. Using data from the Census of Agriculture and taking into consideration both albedo and soil carbon changes, we estimated that from 1981 to 2016, the total radiative forcing for the cropland area in the Canadian Prairies was −405 μW m−2 due to the conversion of CT to either NT or RT and about 70% was due to the change in albedo. During the same period, the total radiative forcing was −410 μW m−2 due to a reduction in the area under summer fallow and about 62% was due to the change in albedo. The equivalent atmospheric CO2 drawdown from these two management changes from albedo change was about 7.8 and 8.7 Tg CO2 yr−1, respectively. These results demonstrate that it is important to consider both the changes of soil carbon and surface albedo in evaluating climate change impacts due to agricultural management practices.

Investigation of Spatial and Temporal Changes in the Land Surface Albedo for the Entire Chinese Territory

Currently, global climate change (GCC) and the urban heat island (UHI) phenomena are becoming serious problems, partly due to the artificial construction of the land surface. When sunlight reaches the land surface, some of it is absorbed and some is reflected. The state of the land surface directly affects the surface albedo, which determines the magnitude of solar radiation reflected by the land surface in the daytime. In order to better understand the spatial and temporal changes in surface albedo, this study investigated and analyzed the surface albedo from 2000 to 2016 (2000, 2008, and 2016) in the entire Chinese territory, based on the measurement database obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, aboard NASA’s Terra satellite. It was shown that the Northeast China exhibited the largest decline in surface albedo and North China showed the largest rising trend of surface albedo from 2000 to 2016. The correlation between changes in surface albedo and the Normalized Difference Vegetation Index (NDVI) indicated that the change trend of surface albedo was opposite to that of NDVI. In addition, in order to better understand the distribution of surface albedo in the entire Chinese territory, the classifications of surface albedo in three years (2000, 2008, and 2016) were implemented using five classification methods in this study.

The Saharan convective boundary layer structure over large scale surface heterogeneity: A large eddy simulation study

Extreme atmospheric and surface conditions over the vast Saharan desert result in the development of one of the deepest atmospheric boundary layers (Saharan Atmospheric Boundary Layer, SABL) on the planet. The land cover in the Sahara mainly consists of wide interchanging areas of stony and sandy desert intercepted by narrower bare rock formations. Significant changes in surface albedo, surface temperature, turbulence fluxes and wind speed have been observed with remote measurement platforms like aircraft and satellites. This was a motivation to simulate the convective boundary layer (CBL) that develops over the heterogeneous Saharan surface with a two-way coupled system of a large eddy simulation code (LES) and a land surface model (LSM). Initial and boundary conditions are provided by airborne observations and mesoscale atmospheric simulations. In order to investigate the effect of surface heterogeneity on the vertical structure of the SABL, a large scale (larger than 10 km) idealized warm surface anomaly is simulated and analyzed. A land strip with a low surface albedo produces almost doubled fluxes in density and stronger convergence near the ground than over the surrounding brighter surfaces. First and second order turbulence statistics reveal that strong thermals penetrate the inversion layer above the CBL producing a vigorous exchange between unstable and overlying stable air. Furthermore, a convective internal boundary layer (CIBL) is formed over the warm strip. The downwind development of the CIBL is studied and CBL depth equations from literature are revised. The average turbulent structure of the SABL reveals flow changes locally and downwind of the surface heterogeneity (strip), which can be more significant than the dispersive fluxes due to surface heterogeneity, and may have an important effect on processes such as dust uplift and its long range transport that influence weather and climate globally.