Jaeil Cho

Incorporating Anthropogenic Water Regulation Modules into a Land Surface Model

AbstractAnthropogenic activities have been significantly perturbing global freshwater flows and groundwater reserves. Despite numerous advances in the development of land surface models (LSMs) and global terrestrial hydrological models (GHMs), relatively few studies have attempted to simulate the impacts of anthropogenic activities on the terrestrial water cycle using the framework of LSMs. From the comparison of simulated terrestrial water storage with the Gravity Recovery and Climate Experiment (GRACE) satellite observations it is found that a process-based LSM, the Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO), outperforms the bucket-model-based GHM called H08 in simulating hydrologic variables, particularly in water-limited regions. Therefore, the water regulation modules of H08 are incorporated into MATSIRO. Further, a new irrigation scheme based on the soil moisture deficit is developed. Incorporation of anthropogenic water regulation modules significantly improves river di...

Testing the hypothesis on the relationship between aerodynamic roughness length and albedo using vegetation structure parameters

Surface albedo (α) and aerodynamic roughness length (z0), which partition surface net radiation into energy fluxes, are critical land surface properties for biosphere–atmosphere interactions and climate variability. Previous studies suggested that canopy structure parameters influence both α and z0; however, no field data have been reported to quantify their relationships. Here, we hypothesize that a functional relationship between α and z0 exists for a vegetated surface, since both land surface parameters can be conceptually related to the characteristics of canopy structure. We test this hypothesis by using the observed data collected from 50 site-years of field measurements from sites worldwide covering various vegetated surfaces. On the basis of these data, a negative linear relationship between α and log(z0) was found, which is related to the canopy structural parameter. We believe that our finding is a big step toward the estimation of z0 with high accuracy. This can be used, for example, in the parameterization of land properties and the observation of z0 using satellite remote sensing.

Application of temperature, water stress, CO2 in rice growth models

In recent decades, numerous studies have attempted to project the impact of hypothesised anthropogenic climate change on rice production. In this study, we offer a comprehensive review of our current understanding related to temperature, CO2, and water-demand parameters in rice growth models. As to future rice yield, night time temperature should be focused in the models as well as day time temperature owing to the contribution of temperature on the night time respiration. Furthermore, although CO2-enhanced photosynthesis is critical for the accurate prediction of rice production in a higher CO2 atmosphere, we found that recent well-developed photosynthesis-stomatal model cannot realize the variation of CO2 stomatal sensitivity with humidity conditions. To estimate water stress under projected climate-change conditions, rice growth model should be required to link with water resource model, which includes natural processes and anthropogenic regulations. The understanding of abilities and limitations in the models is important not only to improve the schemes that models employ, but to also critically review the simulated results.

On the relationship between the Bowen ratio and the near-surface air temperature

The sensitivity of land surface energy partitioning to near-surface air temperature (Ta) is a critical issue to understand the interaction between land surface and climatic system. Thus, studies with in situ observed data compiled from various climates and ecosystems are required. The relations derived from such empirical analyses are useful for developing accurate estimation methods of energy partitioning. In this study, the effect of Ta on land surface energy partitioning is evaluated by using flux measurement data compiled from a global network of eddy covariance tower sites (FLUXNET). According to the analysis of 25 FLUXNET sites (60 site-years) data, the Bowen ratio is found to have a linear relation with the bulk surface resistance normalized by aerodynamic and climatological resistance parameters in general, of which the slope and intercept are dependent on Ta. Energy partitioning in warmer atmosphere is less sensitive to changes in land surface conditions. In addition, a negative relation is found between Bowen ratio and Ta, and this relation is stronger above less vegetated surface and under low vapor pressure deficit and low received radiative energy condition. The empirical results obtained in this study are expected to be useful in gaining better understanding of alternating surface energy partitioning under increasing Ta.

Detecting wildfires with the Korean geostationary meteorological satellite

Satellite remote sensing is a useful tool for monitoring wildfire by analysing the brightness temperature of medium and thermal infrared bands. This letter described a wildfire detection algorithm developed for the COMS (communication, ocean and meteorological satellite) and evaluated the applicability of the proposed method by comparing the detection results with the KFS (Korea Forest Service) wildfire survey data and ASTER (advanced spaceborne thermal emission and reflection radiometer) image. We detected various size of wildfires occurred in South Korea on 9 March 2013, which is a remarkable outcome when considering the limited channels of the COMS. For a more reliable algorithm, the characterization of subpixel fires using Dozier’s method or the multiple endmember spectral mixture analysis will be necessary as future work. In addition, more wildfire cases should be experimented for statistical assessment of the accuracy.

Assessment of the relationship between thermal-infrared-based temperature−vegetation dryness index and microwave satellite-derived soil moisture

Soil moisture (SM) is an important parameter in terrestrial ecological and hydrological processes, particularly in arid and semi-arid regions. However, a highly accurate SM grid data set, which is used as a reference for the data quality, is not really suitable for the validation of other SM products. Thus, a more effective method may be necessary for evaluation of SM grid data. The temperature−vegetation dryness index (TVDI), which is estimated by the relationship between land surface temperature and vegetation index data, has been developed to assess regional water stress. Based on previous studies, we assumed a negative linear relationship between SM and the TVDI to establish the evaluation method of SM grid data. Although a highly accurate measure of SM obtained by use of microwave sensors may not always exhibit a negative linear correlation with the TVDI, the pixels of strong negative linear correlation between them signifies at least a higher accuracy of the two data at that position. The negative relationships between microwave satellite sensor-derived SM and the TVDI were tested by application of 16-day scaled satellite data in the Sahel. We determined that the correlations differ spatially according to vegetation distribution. That is, when compared with a lower correlation in the arid Sahara to the north, a higher correlation (−0.9 < r < −0.7) was observed in the savannas, shrublands, and grasslands to the south. Our comparison results will be useful in developing validation methodologies for SM grid data in an alternative way under conditions of insufficient in situ measurements.

Satellite-based assessment of large-scale land cover change in Asian arid regions in the period of 2001–2009

Abstract Arid regions in Asia are commonly characterized by rapidly growing populations with limited land resources and varying rainfall frequencies under climatic change. Despite being one of the most important environmental challenges in Asia, the changing aridity in this region, particularly due to large-scale land cover change, has not been well documented. In this study, we used rainfall data and a new land heterogeneity index to identify recent trend in land cover changes in the Asian arid regions. The result indicates a significant decreasing trend of barren lands and an increasing trend of vegetated lands. Although the potential land cover change is commonly believed to be strongly sensitive to rainfall change, such sensitivity has not been observed during the nine-year period (2001–2009) analyzed. Through the analyses of two separate periods (2001–2005 and 2005–2009), the sensitivity of rainfall to land cover change in arid regions is found to be dependent on the initial spatial heterogeneity of vegetated land cover. The approach used and the findings in this study represent an important step toward better understanding of large-scale land cover change in the Asian arid regions, and have the potential to predict future land cover change under various climate change scenarios.

First retrieval of fire radiative power from COMS data using the mid-infrared radiance method

ABSTRACT Fire radiative power (FRP), which is the power radiated by fire within a unit area, is a fundamental component for estimation of fire emissions. Successive information of FRP is provided by instruments on geostationary satellites, such as the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board Meteosat, and the Imager on board Geostationary Operational Environmental Satellite (GOES) for Europe, Africa and America. In East Asia, however, the geostationary satellites such as Multifunctional Transport Satellite, Himawari, Fengyun, and Communication, Ocean and Meteorological Satellite (COMS) do not provide official FRP products yet. This article describes the first retrieval of COMS FRP using the mid-infrared radiance method with an optimal sensor coefficient derived from our experimental simulations. The COMS FRP retrievals were compared with Moderate Resolution Imaging Spectroradiometer (MODIS) FRP products in East Asia for each April during 2011–2014. The mean absolute percentage difference was approximately 17%, which is comparable with the results of SEVIRI (30%) and GOES (17%) against MODIS FRP even if their experiment conditions were slightly different. The retrieval accuracies of the COMS FRP had almost no dependence on land-cover types and the size of fire, which can be interpreted a stable outcome covering most wildfire situations, although parts of the pixels showed somewhat low accuracies according to viewing and solar zenith angles. The results of our study can be useful to understand spatiotemporal variations of wildfire emissions. Furthermore, it can be a reference for FRP retrievals of the next-generation geostationary satellites such as the latest Himawari-8 and the forthcoming Geostationary Korean Multipurpose Satellite 2A.

Satellite-based assessment of Amazonian surface dryness due to deforestation

ABSTRACT Intensive deforestation due to human activities has been occurring in the Amazon over the last several decades, leading to a projected decrease in precipitation due to reduced evapotranspiration (ET) according to the prediction by climate model experiments. Such hydrological and climatic changes are closely related to the drying of soil moisture (SM) as a source of atmospheric water vapour via evaporation. We used a satellite-observed index, temperature-vegetation dryness index (TVDI), to assess the impact of deforestation on SM during the dry season. Thirteen-year (2002-2014) data for three representative areas (forest, deforesting and deforested) in the Rondônia, southwest (SW) of Amazon were used to evaluate the relative changes in SM corresponding to the extent of deforestation. We found the increase in dryness in the deforested Amazon using the moderate resolution imaging spectroradiometer (MODIS) satellite sensor. Furthermore, given that the impact of forest removal on surface SM can be distinguished from the associated changes in precipitation and vegetation conditions, it is found that the relative proportion of deforested areas is linearly correlated with that of SM. The results from this study are useful to validate climate model simulations of deforestation and to improve our understanding on the biophysical controls of Amazon deforestation.

On the relationships between satellite-based drought index and gross primary production in the North Korean croplands, 2000–2012

ABSTRACT Drought is one of the main constraints on vegetation growth and crop yields, although land ecosystems differ in their sensitivity to drought. Satellite-based vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), have been used in many drought studies, but they may not sufficiently represent the water content of vegetated land. Alternatively, the Normalized Difference Drought Index (NDDI) has been developed by integrating the NDVI and Normalized Difference Water Index (NDWI). In this letter, we examine how drought affects crop growth by quantifying the relationships between NDDI and the Gross Primary Production (GPP) derived from the moderate-resolution imaging spectroradiometer. In the North Korean croplands, NDDI had a strong negative correlation with GPP during 2000–2012. The relationships were more significant under relatively dry conditions (e.g., dry seasons or dry regions). The impacts of NDDI on GPP was greater in summer than in spring, which indirectly shows summer drought may be more critical to crop productivity. The NDDI–GPP relationship was slightly time-lagged in spring, which indicates that vegetation productivity may not always respond instantly to surface dryness. The NDDI can be a viable option for measuring the impacts of drought on vegetation and agriculture over a wide area.