| Yarlung Zangbo River is located in the Qinghai-Tibet Plateau. The basin is extremely sensitive and fragile to the global climate change, due to the impact of special topographical features and high altitude plateau. As the Tibet's most important economic region, the runoff change of Yarlung Zangbo River basin has a significant impact on the national economy around and people's lives. Thus, in the global context of climate change, the study of water resources change characters and its response to the global climate change in the Qinghai-Tibetan Plateau will provide insights into the water circulation and the evolution law of water resources in the alpine area, has deep significance for the maintenance of water and land resources balance, but also has practical significance and long-term significance for the rational exploitation of water resources in the Yarlung Zangbo River basin.Choosing the Yarlung Zangbo River basin as the study area, through the analysis of hydrological elements change law and spatial and temporal patterns change of the land use/land over, in the paper, the impact of climatic factors such as the precipitation, temperature, evaporation and driver factor of LUCC on the runoff is discussed. The main results and conclusions of the study are drawn as follows:(1)The annual mean temperature of 1960-2009 in the Yarlung Zangbo River basin had a significant upward trend, which increased with the ascent of the altitude. In addition, the minimum temperature tendency rate was much higher than the maximum one, and the rising rate of minimum temperature was about two times more than the maximum one. It showed that the warming of temperature occurred mainly at night in the Qinghai-Tibetan Plateau. The general distribution trend of annual mean temperature in the Yarlung Zangbo River basin was approximately fit for the terrain, with a decreasing trend from southeast to northwest. Jiali was the smallest temperature boost area with the range of 0.18-0.20℃/10a. Lhasa was the largest temperature boost region with the range of 0.55-0.58℃/10a. Mutation testing for mean temperature time series of the basin showed that the abrupt change points of mean temperature series emerged in 1987 and 1997.(2)The annual precipitation of 1960-2009 in the basin had an upward trend, but not significant, and the precipitation change showed complex. The trend of precipitation spatial distribution was decreasing from southeast to northwest which was similar with the mean temperature change of the basin. With the center of Bomi, the precipitation tendency rate of the basin had a gradually decreasing outward trend. Bomi was the area with the largest increase range of precipitation, while Heyuan was the area with the most obvious decrease range of precipitation. Compared with the mean temperature mutation signals, precipitation in the basin was obviously weaker. After further analysis, it was shown that the precipitation of the Yarlung Zangbo River basin was in the process of slow rising with two mutations in 1982 and in 1995, and experienced three stages of decrease, increase and decrease again.(3)The precipitation was covariant with the temperature. Use the product of temperature and precipitation change trends Z values after standardization to describe the regions where the two variables had significant simultaneous change trend. It was shown that, the middle reach of the basin had a warm and wet in the annual scale. In the dry season scale, when the basin had a trend of warm and wet monsoon, the product distribution of temperature and precipitation change Z Values was even and with a main warm-dry trend as a whole, due to the spatial distribution difference of precipitation.(4) ETo has obvious characteristics of annual distribution, changes of a year showing a double peak.The mean ET0 of the basin was increasing from southeast to northwest trend. It also means the ET0 was decreasing from upstream to downstream. ET0 was in a universal decreases trend, with the reduced rate of 0.949mm/a for ET0(year),0.546mm/a for ET0(dry season) and 0.403mm/a for ET0(rainy),by the method of linear fitting for the ET0 of the 27 sites and significance tests. That was mainly to say, ETo(year) changes were impacted by the joint function of ETo(dry season) and ETo(rainy).By the analysis of multiple regression, K-means classification and partial correlation, a conclusion that the wind speed was the dominant factor for ET0 changes in the Yarlung Zangbo River basin was taken.(5)After the linear fit of natural runoff in the basin, it was shown that there was a decreasing trend as a whole in the Yarlung Zangbo River Basin, but not obvious. Decadal variation of runoff had cyclical fluctuations, and the annual distribution was extremely imbalance. Through the Mann-Kendall mutation, it was found that, there was a mutation in the early 1970s.The wavelet analysis showed that the four hydrological stations of Yarlung Zangbo River main stream had the same periodicity, the first main period of 19-20a, the second main period of 5-6a.(6) The main types of land use in the basin was grass, secondly unused land and forest land, and the sum areas of these three types reached 94%. Land use dynamic degree and land use transfer matrix were adopted to analyze the characters of LUCC, and it was shown that the land use changed relatively slowly in the past 10 years and the area belonged to the stable Qinghai-Tibet region. Land use types were characterized by transformation from grassland, water area and barren land to forest land, from arable land to construction land. The most significant conversion was the increase of woodland, secondly the reduction of grassland and water area, thirdly the increase of construction land and the decrease of arable land.(7)Through the analysis of the runoff affecting factors, it was shown that the changes of temperature and precipitation were the most direct factors affecting the natural runoff of the Yarlung Zangbo River. Precipitation change was the most important factor of the natural runoff, controlled the evolution of river runoff to a certain degree. In addition, the rising of temperature, increasing of evaporation and retreating of glacier affected the evolution of runoff to a certain extent. The increase of forest, barren lands and construction land area promoted the growth of runoff, but the hydrological effect was relatively small, resulting from the small conversation area of land use.
|
PDF Full Text Request