[Application of wavelet transform to monthly runoff time serial analysis in Zagunao watershed, the upper Minjiang...

Runoff is an important component of regional water resources, and its dynamics is to some extent an indicator of water resources dynamics in a region. To know the runoff dynamics and water resources in a region is essential for the sustainable utilization and planning of water resources, and for the research on hydrological response of vegetation change at watershed scale. To disclose the water resources dynamics in Upper Minjiang River, one of the large reaches of Yangze River in southwest China, this paper analyzed the runoff dynamic features of Zagunao watershed, an important watershed in Minjiang River basin. Multi-Resolution Analysis (MRA) and periodicity analysis were conducted with Dmey wavelet function on the monthly runoff data from 1962 to 2002 observed by Zagunao hydrological station, which provided a data-based approximation on the evolution of monthly runoff in Zagunao watershed. It was found that the runoff dynamics in Zagunao watershed was relatively stable during 1962 - 1978, despite that this period was just in correspondence with the term of intensive deforestation activities in Upper Minjiang River basin. It was also clear that the runoff in Zagunao watershed was increased from 1986 to 1997, which was inconsistent with the commonly accepted viewpoint that the runoff decreased with increasing vegetation cover in forest watershed. However, the increasing trend from 1986 - 1997 was consistent with the research results in Yichang by Wang Wensheng and with the global warming at global and continent scale, which meant that global climate change plays a big role in runoff dynamics in Upper Minjiang River. Periodicity analysis showed that the rich-short water periodicity at the scale of 10 years (120 months) and 5 years (60 months) was 3 and 7 times, respectively, which could provide invaluable information for the eco-hydrological function research of forest landscape in Minjiang river basin and the sustainable utilization of water resources. The results from the case study highlighted that sometimes, it was very necessary to consider the role of global climatic warming in disclosing the hydrological response of land use/cover change at watershed scale, otherwise, it would be difficult to explain some hydrological phenomena.