Abstract
The study uses 30 years of the third generation of Advanced Very-High-Resolution Radiometer (AVHRR) NDVI3g monthly data from 1982 to 2012 to identify the natural clusters and important driving factors of the upstream watersheds in Taiwan through hierarchical cluster analysis (HCA) and redundancy analysis (RDA), respectively. Subsequently, as a result of HCA, six clusters were identified based on the 30 years of monthly NDVI data, delineating unique NDVI characteristics of the upstream watersheds. Additionally, based on the RDA results, environmental factors, including precipitation, temperature, slope, and aspect, can explain approximately 52% of the NDVI variance over the entire time series. Among environmental factors, nine factors were identified significantly through RDA analysis for explaining NDVI variance: average slope, temperature, flat slope, northeast-facing slope, rainfall, east-facing slope, southeast-facing slope, west-facing slope, and northwest-facing slope, which reflect an intimate connection between climatic and orthographic factors with vegetation. Furthermore, the rainfall and temperature represent different variations in all scenarios and seasons. With consideration of the characteristics of the clusters and significant environmental factors, corresponding climate change adaptation strategies are proposed for each cluster under climate change scenarios. Thus, the results provide insight to assess the natural clustering of the upstream watersheds in Taiwan, benefitting future sustainable watershed management.
Highlights
Upstream watersheds play a critical role in the regional hydrologic system and are sensitive to climate change [1]
As upstream watersheds are relatively unaffected by human interventions, the changes observed in upstream watersheds indicate effects of climate change [4]
Apart from the drought between 1993 and 1995, another severe drought occurred in Taiwan during 2002 and 2004, as Hsu et al [69] reported
Summary
Upstream watersheds play a critical role in the regional hydrologic system and are sensitive to climate change [1]. The upstream watersheds usually comprise high mountains containing the headwater zone in a river system [2]. A hydrological event in an upstream watershed may directly influence downstream areas many hundreds of kilometers away, highlighting the crucial ecological role of the upstream watersheds [2]. Compared with downstream areas, upstream watersheds generally comprise high mountains, steep gradients, and high ridges, resulting in low accessibilities and less human interventions. As upstream watersheds are relatively unaffected by human interventions, the changes observed in upstream watersheds indicate effects of climate change [4]
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