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| Titel |
Phenological response of vegetation to upstream river flow in the Heihe Rive basin by time series analysis of MODIS data |
| VerfasserIn |
L. Jia, H. Shang, G. Hu, M. Menenti |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 15, no. 3 ; Nr. 15, no. 3 (2011-03-25), S.1047-1064 |
| Datensatznummer |
250012700
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| Publikation (Nr.) |
 copernicus.org/hess-15-1047-2011.pdf |
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| Zusammenfassung |
| 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. |
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