Land Surface Net Radiation Research Articles

Biogeophysical and biogeochemical impacts of land-use change simulated by MIROC-ES2L

Land-use change is one of the focal processes in Earth system models because it has strong impacts on terrestrial biogeophysical and biogeochemical conditions. However, modeling land-use impacts is still challenging because of model complexity and uncertainty. This study examined the results of simulations of land-use change impacts by the Model for Interdisciplinary Research on Climate, Earth System version 2 for long-term simulations (MIROC-ES2L) conducted under the Land-Use Model Intercomparison Project protocol. In a historical experiment, the model reproduced biogeophysical impacts such as decreasing trends in land-surface net radiation and evapotranspiration by about 1970. Among biogeochemical impacts, the model captured the global decrease of vegetation and soil carbon stocks caused by extensive deforestation. By releasing ecosystem carbon stock to the atmosphere, land-use change shortened the mean residence time of terrestrial carbon and accelerated its turnover rate, especially in low latitudes. Future projections based on Shared Socioeconomic Pathways indicated substantial alteration of land conditions caused primarily by climatic change and secondarily by land-use change. Sensitivity experiments conducted by exchanging land-use data between different future projection baseline experiments showed that, at the global scale, the anticipated extent of land-use conversion would likely play a modest role in the future terrestrial radiation, water, and carbon budgets. Regional investigations revealed that future land use would exert a considerable influence on runoff and vegetation carbon stock. Further model refinement is required to improve its capability to analyze its complicated terrestrial linkages or nexus (e.g., food, bioenergy, and carbon sequestration) to climate-change impacts.

The trends in land surface heat fluxes over global monsoon domains and their responses to monsoon and precipitation

The climatology, trends and leading modes of land surface latent heat flux (LHF) and sensible heat flux (SHF) as well as their responses to monsoon and precipitation in global land monsoon domains are presented. During the past three decades, LHF and SHF have generally undergone a rising and decreasing trend (that is, (LHF+, SHF−)), respectively, in Asian, North African, Austrian, and South American monsoon domains. Moreover, the increasing rate of LHF was higher than the decreasing rate of SHF, which causes a decreased trend in Bowen ratio. Two other dominant trend patterns, (LHF−, SHF−) and (LHF+, SHF+), are observed in South African and South American monsoon domains, respectively. The trends in LHF and SHF are closely linked to increasing global monsoon intensity and precipitation, especially for the monsoon domain that has annual precipitation lower than 1300 mm yr−1. Singular value decomposition (SVD) analyses show that monsoon strength explains 25.2% and 22.2% total covariance of LHF and SHF respectively in the first modes, and that precipitation slightly raises the percentages up to 27.8% and 24% respectively. The increasing monsoon and precipitation on one hand favor more land surface available energy being converted into LHF; on the other hand they enhance the LHF by increasing the land surface net radiation. Moreover, remarkable phase shifts in LHF and SHF are observed for monsoon domains during late-1990s, which are in phase with those of precipitation and monsoon strength. The intensifying LHF and precipitation indicate the acceleration of hydrological cycle in global terrestrial monsoon domains.

Trends of land surface heat fluxes on the Tibetan Plateau from 2001 to 2012

ABSTRACTA parameterization approach of effective roughness length was introduced into the Surface Energy Balance System (SEBS) model to account for subgrid‐scale topographical influences. Regional distribution of land surface heat flux values (including net radiation flux, ground heat flux, sensible heat flux, and latent heat flux) was estimated on the Tibetan Plateau (TP) based on the SEBS model, and utilizing remote sensing products and reanalysis datasets. We then investigated annual trends in these fluxes for the period 2001–2012. It was found that land surface net radiation flux increased slightly, especially in high, mountainous regions and the central TP, and was influenced by glacial retreat and topsoil wetting, respectively. Sensible heat flux decreased overall, especially in the central and northern TP. In the Yarlung Zangbo River (YZR) Basin, the sensible heat flux increased because of a rise in the ground‐air temperature difference. The latent heat flux increased over the majority TP, except for areas in the YZR Basin. This can be attributed to increases in precipitation and vegetation greening.

Scenario Simulation of the Influence of Land Use Change on the Regional Temperature in a Rapidly Urbanizing Region: A Case Study in Southern-Jiangsu, China

It has been shown that land use change in urbanized region, especially urban land expansion, will influence regional climate. However, there has been very little research on the climate effects of the future land use change in a rapidly urbanizing region. Taking the southern part of Jiangsu province in China as the study area and through a scenario analysis, the influence of land use change on the regional temperature was analyzed from the perspective of land surface radiation budget and energy balance. The results indicated that (1) the monthly average temperature is significantly higher under the Rapid Economic Growth (REG) scenario than under the Cooperate Environmental Sustainability (CES) scenario in 2050, especially in the hottest month (July). (2) The range of high-temperature regions is much wider under the REG scenario than it is under the CES scenario in 2050. (3) The land surface net radiation and latent heat flux are two key factors through which land use change influences the regional temperature in the study area, and the latent heat flux plays a dominant role. (4) Land use change mainly influences the land surface net radiation by altering the land surface albedo and emissivity. These results are helpful to mitigate regional climate change effects caused by land use change.

Is Oklahoma getting drier?

Land surface hydrology is important to regional climate, ecosystem, agriculture, and even human activities. Changes in soil moisture can produce considerable impacts on socioeconomics. Analysis of assimilation model results, especially those from the Community Land Model, shows that soil moisture over Oklahoma region is continuously reduced from 1980 to 2009. The potential drying trend in the Oklahoma region is evaluated by observations taken during last three decades in this study. Satellite data from Global Precipitation Climatology Project exhibit a clear precipitation decrease in the Oklahoma region during the last decade or so compared with those of two or three decades ago. Accompanying with the precipitation variation, land surface net radiation and temperature over the region are found increases by satellite and/or in-situ measurements. These changes in regional climate conditions also likely result in reduction of regional evaporation and enhancement of sensible heat transport from land surface into the atmosphere as indicated in assimilated data. These observed and modeled evidences of the changes in regional water and energy cycles lead us to conclude that the soil moisture over the Oklahoma region was reduced during the last decade. This soil moisture drop could increase a risk in water shortage for agriculture in the Oklahoma state if the dry period continues. Further investigations on the drying in the Oklahoma State or even entire Southern Great Plains are needed to mitigate potential droughts, reductions in vegetation products, and other socioeconomic impacts.

A Remote Sensing Study of the NDVI– T s Relationship and the Transpiration from Sparse Vegetation in the Sahel Based on High-Resolution Satellite Data

This article proposes a new approach for estimation of the transpiration rate in sparse canopies. The method relies on a combination of techniques; some of which having a successful background of solid experimental and theoretical justification, while others having only recently been introduced as promising tools for the extraction of environmental information from satellite data. The transpiration rate (λ E v ) is calculated by applying an energy balance approach to the vegetation component of the land surface: λ E v=R n v−H v , where R n v is the net radiation absorbed by the vegetation, and H v is the sensible heat flux between the leaves and the air within the canopy. R n v is calculated through the use of remote sensing and standard meteorological data by combining a conventional method for estimation of the land surface net radiation with a ground-calibrated function of NDVI (normalized differential vegetation index). H v is assessed as a linear function of the temperature difference between vegetation ( T v ) and the mean canopy air stream ( T 0). Because the surface temperature ( T s ) recorded by satellite contains combined information of both soil and vegetation, T v is evaluated on the basis of the linear NDVI– T s relationship for individual surface types. T 0 is assessed utilizing recent evidence that ( T s−T 0) is linearly related to the difference in surface temperature and air temperature above the canopy ( T s−T a ), with the slope coefficient depending only on canopy structure. The method is tested using remote sensing data ranging from ground-based, airborne, and satellite recordings. The modeled transpiration rates compared well to measurements of sapflow data and latent heat fluxes recorded for a wide range of surface types (agricultural crops, natural vegetation, forest vegetation).