Phenological response of vegetation to upstream river flow in the Heihe Rive basin by time series analysis of MODIS data

Liquid and solid precipitation is abundant in the high elevation, upper reach of the Heihe River basin in northwestern China. The development of modern irrigation schemes in the middle reach of the basin is taking up an increasing share of fresh water resources, endangering the oasis and traditional irrigation systems in the lower reach. In this study, the response of vegetation in the Ejina Oasis in the lower reach of the Heihe River to the water yield of the upper catchment was analyzed by time series analysis of monthly observations of precipitation in the upper and lower catchment, river streamflow downstream of the modern irrigation schemes and satellite observations of vegetation index. Firstly, remotely sensed NDVI data acquired by Terra-MODIS are used to monitor the vegetation dynamic for a seven years period between 2000 and 2006. Due to cloud-contamination, atmospheric influence and different solar and viewing angles, however, the quality and consistence of time series of remotely sensed NDVI data are degraded. A Fourier Transform method – the Harmonic Analysis of Time Series (HANTS) algorithm – is used to reconstruct cloud- and noise-free NDVI time series data from the Terra-MODIS NDVI dataset. Modification is made on HANTS by adding additional parameters to deal with large data gaps in yearly time series in combination with a Temporal-Similarity-Statistics (TSS) method developed in this study to seek for initial values for the large gap periods. Secondly, the same Fourier Transform method is used to model time series of the vegetation phenology. The reconstructed cloud-free NDVI time series data are used to study the relationship between the water availability (i.e. the local precipitation and upstream water yield) and the evolution of vegetation conditions in Ejina Oasis from 2000 to 2006. Anomalies in precipitation, streamflow, and vegetation index are detected by comparing each year with the average year. The results showed that: the previous year total runoff had a significant relationship with the vegetation growth in Ejina Oasis and that anomalies in the spring monthly runoff of the Heihe River influenced the phenology of vegetation in the entire oasis. Warmer climate expressed by the degree-days showed positive influence on the vegetation phenology in particular during drier years. The time of maximum green-up is uniform throughout the oasis during wetter years, but showed a clear S-N gradient (downstream) during drier years

L2-L1 word association in bilinguals: Direct evidence

The Revised Hierarchical Model (Kroll and Stewart, 1994) assumes that words in a bilingual’s languages have separate word form representations but shared conceptual representations. Two routes lead from an L2 word form to its conceptual representation: the word association route, where concepts are accessed through the corresponding L1 word form, and the concept mediation route, with direct access from L2 to concepts. To investigate word association, we presented proficient late German-Dutch bilinguals with L2 non-cognate word pairs in which the L1 translation of the first word rhymed with the second word (e.g. GRAP (joke) – Witz – FIETS (bike)). If the first word in a pair activated its L1 equivalent, then a phonological priming effect on the second word was expected. Priming was observed in lexical decision but not in semantic decision (living/non-living) on L2 words. In a control group of Dutch native speakers, no priming effect was found. This suggests that proficient bilinguals still make use of their L1 word form lexicon to process L2 in lexical decision

Analysis of the land surface heterogeneity and its impact on atmospheric variables and the aerodynamic and thermodynamic roughness lengths

The land surface heterogeneity has a very significant impact on atmospheric variables (air temperature T-a, wind speed u, and humidity q), the aerodynamic roughness length z(0m), thermodynamic roughness length z(0h), and the excess resistance to heat transfer kB(-1). First, in this study the land surface heterogeneity has been documented through the comparison of surface reflectance r(0), surface temperature T-0, net radiation flux R-n, and sensible heat flux H partitioning over the different land cover types in the experimental areas of the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment on the Tibetan Plateau (GAME/Tibet), the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project on the Tibetan Plateau (CAMP/Tibet), the Heihe Basin Field Experiment (HEIFE), the Arid Environment Comprehensive Monitoring Plan, 95 (AECMP' 95), and the Dun Huang Experiment (DHEX). The results show that the surface heterogeneity was very significant in the areas of the HEIFE, the AECMP' 95, and the DHEX and that it was less significant in the areas of CAMP/Tibet and GAME/Tibet. Second, the vertical profiles of T-a, u, and q in the near-surface layer and above the blending height z(b) have been analyzed using the atmospheric boundary layer (ABL) tower data, radiosonde data, and tethered balloon data observed during the HEIFE, the DHEX, and the CAMP/Tibet. The results show that the land surface heterogeneity leads in the near-surface layer to different vertical profiles of u, T-a, and q overlying the surfaces of the Gobi and the oasis in the areas of the HEIFE and DHEX. The values of u, T-a, and q become well mixed above a height of about 300 m at the HEIFE and 150 m at the DHEX. z(0m), z(0h), and kB(-1) over the different land surfaces have also been determined in this study. The results show that the land surface heterogeneity leads to different aerodynamic and thermodynamic parameters over the areas of the HEIFE, the AECMP' 95, and the GAME/Tibe

Regional foliar phenology along a sw-ne climatic gradient in Argentina

Se caracteriza la fenología foliar regional de Argentina mediante parámetros diná- micos que describen una serie temporal de nueve años de imágenes mensuales de índice de vegetación NDVI. Se aplica la Transformada Rápida de Fourier. Se analizan las variaciones de los parámetros obtenidos a lo largo del gradiente climático en una transecta SW-NE. Las variaciones del NDVI medio responden a la disponibilidad hídrica. La amplitud a un año refleja la variación intraanual del NDVI: muy baja en condiciones de alta (clima subtropical muy húmedo) y baja (diagonal árida) disponibilidad hídrica, máxima en los bosques andino-patagónicos caducifolios e intermedia en oasis bajo riego y región semiárida. La amplitud a 0,5 año (variabilidad intraanual) caracteriza regiones agrícolas intensivas en secano (dos cosechas anuales). La fase es más corta en regiones húmedas y más largas en regiones áridas. La amplitud a nueve años caracteriza la variabilidad climática interanual de las zonas áridas.Argentina’s regional foliar phenology is characterized through parameters that describe a nine-year time series of monthly NDVI images. Fast Fourier Transform is applied. Variations in the obtained parameters are analyzed across the climatic gradient of a SW-NE transect. Variations in mean NDVI respond to water availability. Amplitude at one year reflects the intra-annual NDVI variation: the lowest amplitudes occur in conditions of high (very wet sub-humid climate) and low (arid diagonal) water availability, the highest amplitudes occur in deciduous Andean-Patagonian forests, and intermediate values in irrigated oasis and semiarid region. Amplitude at 0.5 years (intra-annual variability) characterizes rainfed areas under intensive agriculture. Phase is shorter in wet regions and longer in arid regions. Amplitude at nine years characterizes the inter-annual climate variability in arid zones.Fil: Gonzalez Loyarte, Maria Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Menenti, Massimo. University Of Delft; Países Bajo

Evaluation of algorithms to estimate daily evapotranspiration from instantaneous measurements under all-sky conditions

Instantaneous EvapoTranspiration (ET) can be estimated using a single set of instantaneous observations by polar orbiting satellites during the day. Daily, weekly or monthly total ET is required for hydrological studies and water resources assessment. This requires daily total ET regardless of cloud cover. The daily total ET is usually determined assuming that the evaporative fraction (EF) remains constant during at least the central hours of the day and that the product of EF times the daily total net radiation gives a satisfactory estimate of daily total ET. The impact of cloud cover is rarely discussed. In this paper, we used data collected at two experimental sites in the Heihe River basin in northwestern China: Arou with grassland in an alpine region and Yingke with agricultural crops in a semi-arid region. Two methods were evaluated to determine daily total ET with instantaneous observations: a) self-conservation of evaporative fraction (EF-const); b) assuming the diurnal course of ET is the same sinusoidal function of the time of the instantaneous observation as the solar irradiance (Rs) (ET-Rs). Daily ET calculated with the two methods were evaluated against observed daily values. The results showed that these assumptions did not hold and the accuracy of ET estimates obtained with either method was reduced by: a) diurnal variation of ET and b) the time lag between ET and net radiation under clear skies. Larger errors occurred when applying both methods under cloudy conditions during the growing season, while in the remaining part of the year the impact of cloud cover was lower.</p

Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

The potential of directional observations in the thermal infrared region for land surface studies is a largely uncharted area of research. The availability of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction. In the context of studies on heat transfer at heterogeneous land surfaces, multiangular thermal infrared (TIR) observations offer the opportunity of overcoming fundamental difficulties in modeling sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil. The first one included the use of multi-temporal field measurements at view angles of 0°, 23° and 52°. The second and third one were done with directional ATSR observations at view angles of 0° and 53° only. The first one was a contribution to the Inner-Mongolia Grassland Atmosphere Surface Study (IMGRASS) experiment in China, the second to the Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States. The IMGRASS experiment provided useful insights on the applicability of a simple linear mixture model to the analysis of observed radiance. The HEIFE case study was focused on the large oasis of Zhang-Ye and led to useful estimates of soil and vegetation temperatures. The SGP 1997 contributed a better understanding of the impact of spatial heterogeneity on the accuracy of retrieved foliage and soil temperatures. Limitations in the approach due to varying radiative and boundary layer forcing and to the difference in spatial resolution between the forward and the nadir view are evaluated through a combination of modeling studies and analysis of field data

Bioclimatic map for the travesías (vast plains) of Mendoza province (Argentina) based on foliar phenology

El objetivo fue generar un mapa bioclimático de la llanura de Mendoza que reflejara las diferencias climáticas expresadas por la actividad de la vegetación (fenología foliar) a escala regional. Se partió de la imagen digital del índice bioclimático de aridez P/ETP, generada en una etapa anterior a partir de una serie temporal de imágenes de índice verde (IVDN), y se recodificó en clases bioclimáticas. Se evaluó en cada clase la influencia antrópica y edáfica sobre las condiciones climáticas de aridez reflejadas por la vegetación. Se graficó la marcha fenológica anual media para cada bioclima a partir de una reconstrucción del IVDN. Las clases de clima húmedo y subhúmedo son de carácter edáfico debido al riego (oasis). Se proponen las clases: subdesértico (8,4%), árido inferior (15,3%), árido superior (24,2 %), semiárido inferior (25%) y semiárido superior (27,1%). Cada bioclima tiene una expresión vegetativa diferente en condiciones naturales. La marcha fenológica anual muestra que a mayor aridez menor es el contraste entre el IVDN mínimo y máximo, y que el momento de máxima cobertura vegetal varía de enero (semiárido) a abril (subdesértico). Esta propuesta permite extender y optimizar el conocimiento climático de las estaciones meteorológicas a través de toda la llanura mediante la expresión fenológica de la vegetación.The aim was to propose a bioclimatic map of the plain of Mendoza province reflecting the climatic differences expressed by vegetation activity (foliar phenology) at regional scale. The digital image of the bioclimatic aridity index P/ETP, resulting from a previous research on time series of NDVI images, was recoded into bioclimatic classes. Each class was analysed, assessing whether factors such as soil or human activities are influencing aridity, as expressed by vegetation. Mean annual phenological rhythm was graphed for each bioclimate by reconstructing the yearly NDVI curve. Results show that humid and subhumid classes are due to irrigation. The proposed map presents five classes: subdesert (8.4%), lower arid (15.3%), upper arid (24.2%), lower semiarid (25%) and upper semiarid (27.1%). Each climatic class has a different expression of vegetation activity under natural conditions, all year long. The phenological rhythm shows that aridity reduces the contrast between minimum and maximum NDVI and that time of maximal vegetation cover varies from January, under semiarid climate, to April, in subdesert climate. This proposal allows enhancement and optimization of meteorological data throughout the whole plain by means of vegetation phenology.Fil: González Loyarte, María Margarita. Instituto Argentino de Investigaciones de las Zonas Áridas Fil: Menenti, Massimo. Istituto per i Sistemi Agricoli e Forestali del Mediterraneo (Italia)Fil: Diblasi, Ángela. Universidad Nacional de Cuyo. Facultad de Ciencias Económica