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

Abstract

Abstract. 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

Estimation of Aerodynamic Roughness Length over Oasis in the Heihe River Basin by Utilizing Remote Sensing and Ground Data

“…The HANTS is a method for time series analysis and reconstruction based on the principles of Fourier Transform by decomposing a periodical series into Fourier components and it is a reliable method commonly used by many researchers for time series reconstruction [36]. HANTS has multiple advantages: It can deal with time series with irregularly spaced observations, detect outliers automatically, and capture the complex phenology of land cover by estimating the amplitude and phase of the periodic components used to model the NDVI time series [37,38]. Figure 2 shows an example of the original and reconstructed time series of NDVI using the HANTS approach.…”

Monitoring of Evapotranspiration in a Semi-Arid Inland River Basin by Combining Microwave and Optical Remote Sensing Observations

“…For some time periods that cloud cover can persist longer than the compositing period; these compositing schemes cannot eliminate atmospheric contamination. Therefore a time series reconstruction algorithm proposed by Jia et al [55] based on the Harmonic Analysis of Time Series (HANTS) approach and the Temporal-Similarity-Statistics (TSS) method was implemented to obtain daily cloud-free NDVI time series being consistent at spatial and temporal scales.…”

Relating seasonal dynamics of enhanced vegetation index to the recycling of water in two endorheic river basins in north-west China

“…Kang et al, 1999;Gates et al, 2008a;Huo et al, 2008;Li et al, 2008;Jia et al, 2011;Ma et al, 2009Ma et al, , 2013Pang et al, 2011;Zhuang et al, 2011) make reference to the importance of orographic rainout and the role of oasis vegetation in supporting the water cycle in the Hexi Corridor. However, none of these studies explicitly connects in-mountain production of precipitation to the seasonal evolution of oasis vegetation.…”