Abstract.We analyzed the seasonal variations of energy balance components over three different surfaces: irrigated cropland (Yingke, YK), alpine meadow (A'rou, AR), and spruce forest (Guantan, GT). The energy balance components were measured using eddy covariance (EC) systems and a large aperture scintillometer (LAS) in the Heihe River Basin, China, in 2008 and 2009. We also determined the source areas of the EC and LAS measurements with a footprint model for each site and discussed the differences between the sensible heat fluxes measured with EC and LAS at AR. The results show that the main EC source areas were within a radius of 250 m at all of the sites. The main source area for the LAS (with a path length of 2390 m) stretched along a path line approximately 2000 m long and 700 m wide. The surface characteristics in the source areas changed with the season at each site, and there were characteristic seasonal variations in the energy balance components at all of the sites. The sensible heat flux was the main term of the energy budget during the dormant season. During the growing season, however, the latent heat flux dominated the energy budget, and an obvious "oasis effect" was observed at YK. The sensible heat fluxes measured by LAS at AR were larger than those measured by EC at the same site. This difference seems to be caused by the so-called energy imbalance phenomenon, the heterogeneity of the underlying surfaces, and the difference between the source areas of the LAS and EC measurements.

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Drought has been a concern of global and regional water, carbon and energy cycles. From 1999 to 2011, North China experienced a multiyear precipitation reduction, which decreased significantly water availability as indicated by decreased soil moisture and Palmer Drought Severity Index. In this study, three light use efficiency models (CASA, MODIS-GPP and EC-LUE) and one dynamic vegetation model (IBIS) were used to characterize the impacts of long-term drought on terrestrial carbon fluxes over the North China. All of four models showed the reduction in averaged GPP of 0.026–0.047 Pg C yr⁻¹ from 1999 to 2011 compared to 1982–2011. Based on IBIS model, simulated ecosystem respiration fell from 1999 to 2011 by 0.016 Pg C yr⁻¹. Multiple precipitation reduction changed the regional carbon uptake of 0.0014 Pg C yr⁻¹ from 1982 to 1998 to a~net source of 0.018 Pg C yr⁻¹. Moreover, a pronounced decrease of maize yield was found ranging from 1999 to 2011 versus the average of 1978–2011 at almost all provinces over the study region. The largest reduction of maize yield occurred in the Beijing (2499 kg ha⁻¹ yr⁻¹), Jilin (2180 kg ha⁻¹ yr⁻¹), Tianjing (1923 kg ha⁻¹ yr⁻¹) and Heilongjiang (1791 kg ha⁻¹ yr⁻¹), and maize yield anomaly was significantly correlated with the precipitation through May and September over the entire study area. Our results revealed that recent climate change, and especially drought-induced water stress, is the dominant cause of the reduction in the terrestrial carbon sink

Abstract. Validation of remote sensing land products is a fundamental issue for Earth observation. Ministry of Science and Technology of the People’s Republic of China (MOST) has launched a high-tech R&D Program named ‘Development and experimental verification of key techniques to validate remote sensing products’ in 2011. This paper introduces the background, scientific objectives, research contents of this project and research result already achieved. The objectives of this project include (1) to build a technical specification for the validation of remote sensing products; (2) to investigate the performance, we will carry out a comprehensive remote sensing experiment on satellite - aircraft - ground truth and then modify Step 1 until reach the predefined requirement; (3) to establish a validation network of China for remote sensing products. In summer 2012, with support of the Heihe Watershed Allied Telemetry Experimental Research (HiWATER), field observations have been successfully conducted in the central stream of the Heihe River Basin, a typical inland river basin in northwest China. A flux observation matrix composed of eddy covariance (EC) and large aperture scintillometer (LAS), in addition to a densely distributed eco-hydrological wireless sensor network have been established to capture multi-scale heterogeneities of evapotranspiration (ET), leaf area index (LAI), soil moisture and temperature. Airborne missions have been flown with the payloads of imaging spectrometer, light detection and ranging (LiDAR), infrared thermal imager and microwave radiometer that provide various scales of aerial remote sensing observations. Satellite images with high resolution have been collected and pre-processed, e.g. PROBA-CHRIS and TerraSAR-X. Simultaneously, ground measurements have been conducted over specific sampling plots and transects to obtain validation data sets. With this setup complex problems are addressed, e.g. heterogeneity, scaling, uncertainty, and eventually to fulfill the purpose of validation of remote sensing land products at pixel scale over heterogeneous surfaces.