Vegetation NDVI Linked to Temperature and Precipitation in the Upper Catchments of Yellow River
Hao, F. ; Zhang, X. ; Ouyang, W. ; Skidmore, A.K. ; Toxopeus, A.G. - \ 2012
Environmental Modeling and Assessment 17 (2012)4. - ISSN 1420-2026 - p. 389 - 398.
land-cover changes - qinghai-xizang plateau - net primary production - central new-mexico - tibetan plateau - modis - china - soil - climate - basin
Vegetation in the upper catchment of Yellow River is critical for the ecological stability of the whole watershed. The dominant vegetation cover types in this region are grassland and forest, which can strongly influence the eco-environmental status of the whole watershed. The normalized difference vegetation index (NDVI) for grassland and forest has been calculated and its daily correlation models were deduced by Moderate Resolution Imaging Spectroradiometer products on 12 dates in 2000, 2003, and 2006. The responses of the NDVI values with the inter-annual grassland and forest to three climatic indices (i.e., yearly precipitation and highest and lowest temperature) were analyzed showing that, except for the lowest temperature, the yearly precipitation and highest temperature had close correlations with the NDVI values of the two vegetation communities. The value of correlation coefficients ranged from 0.815 to 0.951 (p <0.01). Furthermore, the interactions of NDVI values of vegetation with the climatic indicators at monthly interval were analyzed. The NDVI of vegetation and three climatic indices had strong positive correlations (larger than 0.733, p <0.01). The monthly correlations also provided the threshold values for the three climatic indictors, to be used for simulating vegetation growth grassland under different climate features, which is essential for the assessment of the vegetation growth and for regional environmental management.
Parameterization of heat fluxes at heterogeneous surfaces by integrating satellite measurements with surface layer and atmospheric boundary layer observations
Ma, Y.M. ; Menenti, M. ; Feddes, R.A. - \ 2010
Advances in atmospheric sciences 27 (2010)2. - ISSN 0256-1530 - p. 328 - 336.
remote-sensing parameterization - balance system sebs - land-surface - tibetan plateau - reflectance - temperature - meteorology - climate - area
The regional heat flux exchange between heterogeneous landscapes and the nearby surface layer (SL) is a key issue in the study of land-atmosphere interactions over arid areas such as the Heihe River basin in northwestern China and in high elevation areas such as the Tibetan Plateau. Based on analysis of the land surface heterogeneity and its effects on the overlying air flow, the use of SL observations, atmospheric boundary layer (ABL) observations, and satellite remote sensing (RS) measurements along with three parameterization methodologies (here, termed as the RS, tile, and blending approaches) have been proposed to estimate the surface heat flux densities over heterogeneous landscapes. The tile and blending approaches have also been implemented during HEIhe basin Field Experiment (HEIFE), the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project on the Tibetan Plateau (CAMP/Tibet), the Arid Environment Comprehensive Monitoring Plan’ 95 (AECMP'95), and the DunHuang Experiment (DHEX). The results showed that these two proposed parameterization methodologies can be accurately used over heterogeneous land surfaces
Vegetation response to 30 years hydropower cascade exploitation in upper stream of Yellow River
Ouyang, W. ; Skidmore, A.K. ; Hao, F.H. ; Zhao, C. ; Lin, C. - \ 2010
Communications in Nonlinear Science and Numerical Simulation 15 (2010)7. - ISSN 1007-5704 - p. 1928 - 1941.
land-use - dam construction - tibetan plateau - sediment load - impacts - china - landscape - climate - basin - area
The accumulated response of vegetation successive dam constructions and operations is an important concern, but the systematic assessment of impacts induced by cascade hydropower exploitation over long periods are seriously lacking. Using remote sensing data, the variations in grassland, the principal land cover in the upper catchment of the Yellow River, were investigated for eight dams constructed during the period 1977-2006. Two different scales-watershed scale and on-site area-were used to compare the changes in grassland and water area. Correlation coefficients from regression analyses showed that grassland area had more significant interactions with hydropower exploitation indicators in on-site scale than in watershed scale. The hydropower exploitation indicators had a more complex correlation with water area in watershed scale than in on-site scale. Consequently, observations of grassland area responses to successive hydropower exploitations were focused on the on-site region. The Normalized Difference Vegetation Index (NDVI) and the standardized NDVI, which can be used to analyze inter-annual climatic differences, were applied to identify the most heavily influenced vegetation zones. For different hydrological and micro-climatic conditions, the vegetation zones around reservoirs and along the main stream of Yellow River were analyzed, respectively. Two NDVI spatial principles at varied distances from the water demonstrated that the vegetation NDVI was recovering from 1994 to 2006. For distance of less than 10 km from water, the vegetation around reservoirs was better as the higher NDVI in 2006 than in 1977. The inter-annual NDVI comparison demonstrated that the critically affected vegetation zone was concentrated at distances of 0.1-0.4 and 1-6 km from the water. In on-site region, the grassland was further analyzed with elevation and aspect information, which indicated that grassland in sunny aspects was much disturbed. Detailed information about grassland response with water distance and the degradation characteristics provide the comprehensive assessment by cascade hydropower exploitation
Evaluating parameterizations of aerodynamic resistance to heat transfer using field measurements
Liu, S. ; Lu, L. ; Mao, D. ; Jia, L. - \ 2007
Hydrology and Earth System Sciences 11 (2007)2. - ISSN 1027-5606 - p. 769 - 783.
atmospheric surface-layer - flux-profile relationships - boundary-layer - tibetan plateau - evapotranspiration - stability - models
Parameterizations of aerodynamic resistance to heat and water transfer have a significant impact on the accuracy of models of land - atmosphere interactions and of estimated surface fluxes using spectro-radiometric data collected from aircrafts and satellites. We have used measurements from an eddy correlation system to derive the aerodynamic resistance to heat transfer over a bare soil surface as well as over a maize canopy. Diurnal variations of aerodynamic resistance have been analyzed. The results showed that the diurnal variation of aerodynamic resistance during daytime (07:00 h-18:00 h) was significant for both the bare soil surface and the maize canopy although the range of variation was limited. Based on the measurements made by the eddy correlation system, a comprehensive evaluation of eight popularly used parameterization schemes of aerodynamic resistance was carried out. The roughness length for heat transfer is a crucial parameter in the estimation of aerodynamic resistance to heat transfer and can neither be taken as a constant nor be neglected. Comparing with the measurements, the parameterizations by Choudhury et al. (1986), Viney (1991), Yang et al. (2001) and the modified forms of Verma et al. (1976) and Mahrt and Ek (1984) by inclusion of roughness length for heat transfer gave good agreements with the measurements, while the parameterizations by Hatfield et al. (1983) and Xie (1988) showed larger errors even though the roughness length for heat transfer has been taken into account.
An analytical algorithm for the determination of vegetation leaf area index from TRMM/TMI data
Wen, J. ; Su, Z. - \ 2004
International Journal of Remote Sensing 25 (2004)6. - ISSN 0143-1161 - p. 1223 - 1234.
soil-moisture retrieval - surface-temperature - microwave emission - tibetan plateau - polarization - field - ndvi - ghz
In this paper, an analytical algorithm for the determination of land surface vegetation Leaf Area Index (LAI) with the passive microwave remote sensing data is developed. With the developed algorithm and the Tropical Rainfall Measuring Mission/Microwave Imager (TRMM/TMI) remote sensing data collected during the Global Energy and Water Experiment (GEWEX) Asian Monsoon Experiment in Tibet (GAME/Tibet) Intensive Observation Period (IOP'98), the regional and temporal distributions of the land surface vegetation LAI have been evaluated. To validate the developed algorithm and the retrieval results, the maximum-composite Normalized Difference Vegetation Index (NDVI) data over the same study area and period are used in this study; the cloud contaminated NDVI values have been replaced by the cloud-free values reconstructed by the Harmonic ANnalysis of Time Series (HANTS) technique. The results show that the retrieved LAI is in good agreement with the cloud-free NDVI in regional and temporal distributions and in their statistical characteristics; the vegetation characteristics can be clearly assessed from the regional distribution of the retrieved LAI. As lower frequency microwave radiation can penetrate atmosphere and thin cloud layer, with the application of the passive microwave remote sensing data, the developed algorithm can be used to monitor the land surface vegetation condition more effectively.