scholarly journals Competing Effects of Vegetation on Summer Temperature in North Korea

2021 ◽  
Author(s):  
Jieun Oh ◽  
Eungul Lee
Keyword(s):  
Surface Energy ◽  
North Korea ◽  
Large Scale ◽  
Vegetation Index ◽  
Bowen Ratio ◽  
Summer Temperature ◽  
Heat Fluxes ◽  
Cooling Effect ◽  
Western Region ◽  
The Western Region

Abstract Vegetation reduction could affect regional climate by perturbing the surface energy and moisture balances via changes in albedo and evapotranspiration. However, it is unknown whether vegetation effects on climate occur in North Korea, where a severe reduction in forest cover has been observed. This study aimed to identify the biogeophysical processes in vegetation and climate interactions in North Korea, using Normalized Difference Vegetation Index (NDVI) and climate reanalysis data over the period 1982‒2015. As per the NDVI regression trend results, the highest rates of decreasing NDVI were detected in the western region of North Korea during summer. Based on the detrended correlation analysis of NDVI with surface energy variables at each grid point, including solar radiation, sensible and latent heat fluxes, Bowen ratio, and temperature, we identified a cooling effect of vegetation in the western region (with lower NDVI and lower elevation), but a warming effect of vegetation in the northern region (with higher NDVI and higher elevation). The different biogeophysical effects were induced by the increasing and decreasing Bowen ratio with increasing vegetation in the northern and western regions, respectively. In the western region of North Korea, where large-scale human-induced forest loss has been observed, the increasing summer temperature caused by the decreasing cooling effect of vegetation would be up to 1.5 ℃ by the end of this century, if the current rate of deforestation continues. Thus, we urgently suggest that sustainable management and restoration of forests are needed in North Korea, which is among the countries most vulnerable to climate change now and in the future.

scholarly journals An Approach to the Temporal and Spatial Characteristics of Vegetation in the Growing Season in Western China

2020 ◽  
Vol 12 (6) ◽  
pp. 945 ◽  
Author(s):  
Junfang Yuan ◽  
Zhengfu Bian ◽  
Qingwu Yan ◽  
Zhiyun Gu ◽  
Haochen Yu
Keyword(s):  
Standard Deviation ◽  
Vegetation Index ◽  
Growing Season ◽  
Western China ◽  
Vegetation Coverage ◽  
Western Region ◽  
Spatial Characteristics ◽  
Temporal And Spatial ◽  
The Western Region ◽  
Temporal And Spatial Characteristics

Since the implementation of the great western development strategy in 2000, the ecological environment in the western region of China has been significantly improved. In order to explore the temporal and spatial characteristics of vegetation coverage in the western region, this paper adopted the method of Maximum Value Composite (MVC) to obtain the mean Normalized Difference Vegetation Index (NDVI) of vegetation on the basis of the Moderate-resolution Imaging Spector audiometer (MODIS) data of 2000/2005/2010/2015/2018. Thereafter, the spatio-temporal differentiation characteristics of vegetation in western China were analyzed. The results show that: (1) According to the time characteristics of vegetation coverage in the western region, the average annual NDVI value of vegetation coverage in the growing season in the western region fluctuated between 0.12 and 0.15, among which that of 2000 to 2010 fluctuated more greatly but did not show obvious change trend. (2) Based on Sen trend and Mann-Kendall test analysis, the area of vegetation coverage improvement in the western region from 2000 to 2018 was larger than that of significant vegetation degradation. (3) From the perspective of global autocorrelation coefficient, Moran’s I values were all positive from 2000 to 2018, which indicates that the vegetation coverage in the west showed strong positive autocorrelation in each period. According to the average value and coefficient of variation of vegetation coverage, the vegetation coverage was lower in 2000, its internal variation was smaller, and the vegetation coverage increased with time. According to the local spatial autocorrelation analysis, the vegetation coverage levels in different regions varied greatly. (4) The standard deviation ellipse method was used to study the spatial distribution and directional transformation of vegetation. It makes the result more intuitive, and the three levels of gravity center shift, direction shift, and angle shift were considered: the vegetation growth condition in the spatial aggregation area improved in 2015; the standard deviation ellipses in 2000 and 2018 overlapped and shifted eastward, which indicates that the vegetation coverage conditions in the two years were similar and got ameliorated.

scholarly journals Components of near-surface energy balance derived from satellite soundings – Part 2: Noontime latent heat flux

2014 ◽  
Vol 11 (24) ◽  
pp. 7369-7382 ◽  
Author(s):  
K. Mallick ◽  
A. Jarvis ◽  
G. Wohlfahrt ◽  
G. Kiely ◽  
T. Hirano ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Vegetation Index ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Simple Method ◽  
Near Surface ◽  
Available Energy

Abstract. This paper introduces a relatively simple method for recovering global fields of latent heat flux. The method focuses on specifying Bowen ratio estimates through exploiting air temperature and vapour pressure measurements obtained from infrared soundings of the AIRS (Atmospheric Infrared Sounder) sensor onboard NASA's Aqua platform. Through combining these Bowen ratio retrievals with satellite surface net available energy data, we have specified estimates of global noontime surface latent heat flux at the 1°×1° scale. These estimates were provisionally evaluated against data from 30 terrestrial tower flux sites covering a broad spectrum of biomes. Taking monthly average 13:30 data for 2003, this revealed promising agreement between the satellite and tower measurements of latent heat flux, with a pooled root-mean-square deviation of 79 W m−2, and no significant bias. However, this success partly arose as a product of the underspecification of the AIRS Bowen ratio compensating for the underspecification of the AIRS net available energy, suggesting further refinement of the approach is required. The error analysis suggested that the landscape level variability in enhanced vegetation index (EVI) and land surface temperature contributed significantly to the statistical metric of the predicted latent heat fluxes.

scholarly journals Satellite Psychrometric Formulation of the Operational Simplified Surface Energy Balance (SSEBop) Model for Quantifying and Mapping Evapotranspiration

2018 ◽  
Vol 34 (3) ◽  
pp. 555-566 ◽  
Author(s):  
Gabriel B Senay
Keyword(s):  
Remote Sensing ◽  
Energy Balance ◽  
Surface Energy ◽  
Land Surface ◽  
Vegetation Index ◽  
Surface Energy Balance ◽  
Heat Fluxes ◽  
Weather Data ◽  
Time Calibration ◽  
Reference Et

Abstract.Remote sensing-based evapotranspiration (ET) can be derived using various methods, from soil moisture accounting to vegetation-index based approaches to simple and complex surface energy balance techniques. Due to the complexity of fully representing and parameterizing ET sub-processes, different models tend to diverge in their estimations. However, most models appear to provide reasonable estimations that can meet user requirements for seasonal water use estimation and drought monitoring. One such model is the Operational Simplified Surface Energy Balance (SSEBop). This study presents a formulation of the SSEBop model using the psychrometric principle for vapor pressure/relative humidity measurements where the “dry-bulb” and “wet-bulb” equivalent readings can be obtained from satellite-based land surface temperature estimates. The difference in temperature between the dry (desired location) and wet limit (reference value) is directly correlated to the soil-vegetation composite moisture status (surface humidity) and thus producing a fractional value (0-1) to scale the reference ET. The reference ET is independently calculated using available weather data through the standardized Penman-Monteith equation. Satellite Psychrometric Approach (SPA) explains the SSEBop model more effectively than the energy balance principle because SSEBop does not solve all terms of the surface energy balance such as sensible and ground-heat fluxes. The SPA explanation demonstrates the psychrometric constant for the air can be readily adapted to a comparable constant for the surface, thus allowing the creation of a “surface” psychrometric constant that is unique to a location and day-of-year. This new surface psychrometric constant simplifies the calculation and explanation of satellite-based ET for several applications in agriculture and hydrology. The SPA formulation of SSEBop was found to be an enhancement of the ET equation formulated in 1977 by pioneering researchers. With only two key parameters, improved model results can be obtained using a one-time calibration for any bias correction. The model can be set up quickly for routine monitoring and assessment of ET at landscape scales and beyond. Keywords: Dry-bulb, ET fraction, ET modeling, Remote sensing, Satellite psychrometry, Wet-bulb.

scholarly journals Observations of daytime surface energy balance in cloudy tropical conditions at Ile-Ife, Nigeria

MAUSAM ◽  
2022 ◽  
Vol 53 (3) ◽  
pp. 359-366
Author(s):  
O. O. JEGEDE
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Cloud Amount ◽  
Soil Surface ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Average Value ◽  
Tropical Conditions

Daytime energy balance at the surface in cloudy tropical conditions for Ile-Ife; Nigeria (7°33'N, 4°34'E) is investigated based on a series of micrometeorological measurements performed in October/November of 1998. For the humid environment that it is (mixing ratio, 17 -25 g / kg), magnitudes of the latent heat flux were much larger than the values for the sensible heat. Of the morning hours the average value for the Bowen ratio obtained was 0.36, while for the afternoons it was 0.74. As the soil surface became dried up in the afternoons, magnitudes of both sensible heat and ground heat fluxes were found to be comparable.   Fluctuations in the magnitudes of the terms of the surface energy balance correlated well to the cloud amount, degree of soil wetness, air temperature and humidity. But of all these factors, the variation in the amount of cloudiness appeared most dominant.

scholarly journals Surface Energy Components and Land Characteristics of a Rice Paddy

2007 ◽  
Vol 46 (11) ◽  
pp. 1879-1900 ◽  
Author(s):  
Jeng-Lin Tsai ◽  
Ben-Jei Tsuang ◽  
Po-Sheng Lu ◽  
Ming-Hwi Yao ◽  
Yuan Shen
Keyword(s):  
Air Quality ◽  
Surface Energy ◽  
Bowen Ratio ◽  
Rice Paddy ◽  
Carbon Dioxide Flux ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Canopy Resistance ◽  
Rice Paddies ◽  
Quality Models

Abstract Many meteorological and air-quality models require land characteristics as inputs. A field experiment was conducted to study the surface energy budget of a rice paddy in Taiwan. During the day, the energy balance ratio measured by an eddy covariance (EC) system was found to be 95% after considering the photosynthetic and local advected heat fluxes. The observations by the EC system suggest that the Bowen ratio was about 0.18 during the daytime. The EC system also measured the daytime absorbed carbon dioxide flux. The equivalent photosynthetic energy flux was about 1% of the net solar radiation. A reference table describing the land characteristics of rice paddies for use in meteorological and air-quality models is listed that shows that the albedo and the Bowen ratio measured over rice paddies were lower than those listed in many state-of-the-art models. This study proposes simulating latent heat flux by assigning proper values for canopy resistance rather than by assigning constant values for Bowen ratio or surface moisture availability. The diurnal pattern of the canopy resistance of the rice paddy was found to be “U” shaped. Daytime canopy resistance was observed to be 87 s m−1, and a high canopy resistance (∼900 s m−1) should be assigned during nighttime periods.

scholarly journals Evaporation from cultivated and semi-wild Sudanian Savanna in west Africa

2017 ◽  
Vol 21 (8) ◽  
pp. 4149-4167 ◽  
Author(s):  
Natalie C. Ceperley ◽  
Theophile Mande ◽  
Nick van de Giesen ◽  
Scott Tyler ◽  
Hamma Yacouba ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Cover ◽  
West Africa ◽  
Large Scale ◽  
Vegetation Index ◽  
Cultural Beliefs ◽  
Heat Fluxes ◽  
Remotely Sensed Data ◽  
Evaporative Fraction ◽  
Semi Arid

Abstract. Rain-fed farming is the primary livelihood of semi-arid west Africa. Changes in land cover have the potential to affect precipitation, the critical resource for production. Turbulent flux measurements from two eddy-covariance towers and additional observations from a dense network of small, wireless meteorological stations combine to relate land cover (savanna forest and agriculture) to evaporation in a small (3.5 km2) catchment in Burkina Faso, west Africa. We observe larger sensible and latent heat fluxes over the savanna forest in the headwater area relative to the agricultural section of the watershed all year. Higher fluxes above the savanna forest are attributed to the greater number of exposed rocks and trees and the higher productivity of the forest compared to rain-fed, hand-farmed agricultural fields. Vegetation cover and soil moisture are found to be primary controls of the evaporative fraction. Satellite-derived vegetation index (NDVI) and soil moisture are determined to be good predictors of evaporative fraction, as indicators of the physical basis of evaporation. Our measurements provide an estimator that can be used to derive evaporative fraction when only NDVI is available. Such large-scale estimates of evaporative fraction from remotely sensed data are valuable where ground-based measurements are lacking, which is the case across the African continent and many other semi-arid areas. Evaporative fraction estimates can be combined, for example, with sensible heat from measurements of temperature variance, to provide an estimate of evaporation when only minimal meteorological measurements are available in remote regions of the world. These findings reinforce local cultural beliefs of the importance of forest fragments for climate regulation and may provide support to local decision makers and rural farmers in the maintenance of the forest areas.

scholarly journals Cytomegalovirus seroprevalence in pregnant women in the western region of Romania: A large‑scale study

2020 ◽  
Author(s):  
Florin Gorun ◽  
Sorin Motoi ◽  
Daniel Malita ◽  
Dan Navolan ◽  
Dragos Nemescu ◽  
...  
Keyword(s):  
Pregnant Women ◽  
Large Scale ◽  
Western Region ◽  
Large Scale Study ◽  
The Western Region

scholarly journals Environmental Controls on the Surface Energy Budget over a Large Southern Inland Water in the United States: An Analysis of One-Year Eddy Covariance Flux Data

2012 ◽  
Vol 13 (6) ◽  
pp. 1893-1910 ◽  
Author(s):  
Heping Liu ◽  
Qianyu Zhang ◽  
Gordon Dowler
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Large Scale ◽  
The United States ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Vertical Temperature ◽  
Mechanical Mixing ◽  
Air Masses ◽  
Environmental Controls

Abstract The authors analyzed the surface energy fluxes that were measured by an eddy covariance system over the Ross Barnett Reservoir in Mississippi for a 1-yr period in 2008. On a monthly basis over the course of the year, positive vertical temperature and vapor pressure differences were observed, though negative vertical temperature differences occurred occasionally during some short periods when overwater air masses were warmer than the water surface. Consequently, the unstable atmospheric surface layer (ASL) and sufficient mechanical mixing led to positive sensible H and latent λE heat fluxes. The quantities H and λE were distinctively out of phase with the net radiation Rn. The H and λE from the water to the ASL was still substantial on nights with a negative Rn and in winter when Rn was very small. From February to August, approximately 60%–91% of the Rn was used for H and λE, with the remainder being stored in the water. Fueled by the previously stored heat in the water, H and λE exceeded Rn by almost 3 times from September to January. Nighttime evaporation represented a large loss of water (i.e., λE = 82.8 W m−2 at night versus 91.4 W m−2 during the daytime). Intraseasonal and seasonal variations in H and λE were strongly affected by frequent passages of large-scale air masses that were brought in by different synoptic weather systems (e.g., cyclones or anticyclones). The authors’ analysis suggested that this southern reservoir responded to atmospheric forcings on both diurnal and seasonal scales in the same ways as northern lakes of comparable sizes and depths.

Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia

2003 ◽  
Vol 12 (4) ◽  
pp. 333 ◽  
Author(s):  
J. Beringer ◽  
L. B. Hutley ◽  
N. J. Tapper ◽  
A. Coutts ◽  
A. Kerley ◽  
...  
Keyword(s):  
Surface Energy ◽  
Ecosystem Respiration ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Radiative Energy ◽  
Moderate Intensity ◽  
Fire Intensity ◽  
Monsoon Circulation ◽  
Radiative Balance ◽  
Low Intensity

Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post-fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes. These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation.

Surface energy balance closure – the role dispersive fluxes induced by submesoscale secondary circulations

2021 ◽  
Author(s):  
Matthias Mauder
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Eddy Covariance ◽  
Large Scale ◽  
Surface Energy Balance ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Energy Balance Closure ◽  
Secondary Circulations ◽  
Dispersive Fluxes

<p>Quantitative knowledge of the surface energy balance is essential for the prediction of weather and climate. However, a multitude of studies from around the world indicates that the turbulent heat fluxes are generally underestimated using eddy-covariance measurements, and hence, the surface energy balance is not closed. This energy balance closure problem has been heavily covered in the literature for more than 25 years, and as a result, several instrumental and methodological aspects have been reconsidered and partially revised. Nevertheless, a non-negligible energy imbalance remains, and we demonstrate that a major portion of this imbalance can be explained by dispersive fluxes in the surface layer, which are associated with submesoscale secondary circulations. Such large-scale organized structures are a very common phenomenon in the convective boundary layer, and depending on static stability, they can either be roll-like or cell-like and occur even over homogeneous surfaces. Over heterogeneous surfaces, thermally-induced mesoscale circulations can occur in addition to those. Either way, the associated dispersive heat fluxes can inherently not be captured by single-tower measurements, since the ergodicity assumption is violated. As a consequence, energy transported non-turbulently will not be sensed by eddy-covariance systems and a bias towards lower energy fluxes will result. The objective of this research is to develop a model that can be used to correct single-tower eddy-covariance data. As a first step towards this goal, we will present a parametrisation for dispersive fluxes, which was developed based on an idealized high-resolution LES study for homogeneous surfaces, as a function of non-local scaling variables. Secondly, we explore how well this parametrisation works for a number of real-world eddy-covariance sites.</p>

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