Characteristics of the Nujiang River runoff for a long term and its response to climate change

The Nujiang River runoff increases obviously from May each year, and the runoff dominated 81.9% of the gross annual columns during the period from May to October, which is the rainy season over the region. So the mean runoff accounts for 13.65% of the annual columns in each month during the rainy season but only 3% during the dry season. In another word, the menstrual runoff in rainy season is as much as 4.5 times that in other month. It shows that runoff varies greatly with season and the runoff in the rainy season takes the dominant role in annual columns. The analysis of the relationship between the river runoff and precipitation results in that the synchronous correlation coefficient is significant from January to April but the correlation with 1 month lag in the other months except in July. Based on the analyses of precipitation effecting on the river runoff, it is noticed that the precipitation in May affects annual runoff greatly and has a close relationship to the dry season. The annual, rainy season and dry season runoff and precipitation are analyzed by wavelet transform. The results show that the change of precipitation and runoff exhibits the dominant periods with low frequency fluctuation (about 2-4 years), decadal (about 8 years) and interdecadal (about 16 years) oscillations. The change of the annual, rainy season and dry season runoff are consistent with an increased trend, which is evident with 0.05 confidence level except in June and August. The data indicate that the average runoff is increased by 57.6, 28.1 and 85.7 m(3)/s in every 10 years respectively for annual columns, dry season and rainy season. The most obvious change is in October, which increased 111.3 m(3)/s every 10 years. The variation of runoff, temperature and precipitation in Nujiang River drainage basin is primarily consistent. It is revealed that the climate change has resulted in the runoff change in Nujiang. It is increased maximally in October, secondly in May and the increase amount of yearly runoff can achieve about 60 m(3)/S. In the future 20 years, the runoff will decrease in the early phase, but increase in later phase.