Climatic Variability And Impact On Hydrology In Recent 50 Years In Northwest China

Water resources is the major factor acting on the development of the local economy, society and evolves of the eco-environment in Northwestern China. The variety of water resources system was always impacted intensely by climatic change. Taking the water problems as the link, this dissertation studies the impacts of climatic change on water resources system in Northwest China. The research results can be used to provide the scientific basis for the basin comprehensive planning, the productive forces rational distribution, the water resources development and protection, the disaster mitigation, and formulating the sustainable development pattern of the social economy under the global climate change background. Moreover, it may supply the choice reference to the relative departments for formulating the policy and the decision-making to serve for the national economy construction and the sustainable development.This dissertation, taking the climatic change in Northwest China in recent 50 year and the hydrological factors, monthly or annual temperature (T), precipitation (P), actual areal evapotranspiration (ETa), potential evapotranspiration (ETp), Surface Wetness Index (SWI), and net precipitation/runoff depth (NP) as an object, has conducted more thorough research to the impacts of climatic change to the hydrological components with the methods of Mann-Kendall, Standardized Precipitatin Index (SPI) and Morton CRAE. The main results show as follow:1. The patterns of hydro-meteorological factors status quo: (1) The trend of mean annual P is descending from the southeast to the northwest of Northwest China. There are two "wet island" in Qilian Mountain and weast Tianshan Mountain in the northwestern interior region. They has the special significance to the supplies of the moisture content in the interior arid region; (2) The mean annual T of the southeasten of Northwest China and west part of Tarim Basin is high, and middle part, especially north edge of the Qinghai-Tibet Plain, is low; (3) The ETp is dominated by the temperature and precipitation. Because of the low temperature or rich rainfall, the ETp is relatively small in the northwest and southeast area of Northwest China. On the other hand, there is high ETp in the Tarim Basin and the west part of Inner Mongolia; (4) Decided by the moisture content condition, the ETa has the consistent distributed pattern with that of the precipitation in Northwest China; (5) The distribution of SWI presents the pattern which that of the north and south part is high, southwesten, northeast and middle part (Tarim basin, west part of Gansu, and western Inner Mongolian) low; (6) The NP is distributed with the pattern of high value in the south part and low in the north part of Northwest China. The pattern of the distribution of NP has also reflected the human activity in the different location.2. The trend of temperature and precipitation: (1) The area of presenting upward trend of T is bigger than other months in Northwest China in February and October, but in March, April and July through September, it is small. The increasing trend of T is significant in the north part of Hetao district in Inner Mongolian in all of months except August. On the other hand, the trend of T is not significant in south part of Shan'xi Province; (2) The trend of P is not significant in May through August in Northwest China, which dominated the trend of the annual precipitation. The trend of P is downward but not significant in the southeast part of Northwest China, and climate change has a limited affection to this region than west part.3. Calculation of hydrological factors and trend analysis: (1) It was show that the modified CRAE can be used for estimating the ETa in the Northwest China. The results of CRAE not only reflect the characteristic of the regional hydrology, and to some extent reflect the impact of human activities on the local hydrological circulation; (2) Affected by climate change, ETp is increasing in a small area only in February and April. The trend of ETp is downward significantly in July through October and December in centre part of Xinjiang and the west part of Hexi Corridor. There is no significant trend in other months and regions in Northwest China.; (3) For every month's ETa, there are no significant upward trend in Northwest Chnia, but there are some extremely significant decreasing area, which include the centre and south part of Xinjiang, the centre and west of Qinghai, and west of Inner Mongolian. There also have significant downward trend in some region, such as southeast of Gansu and southwest of Shanxi. The trend of ETa is resulted from the annual P and ETp; (4) Related to the change of the local P and ETp, there is a dryer trend in eastrn part of Northwest China in the recent 50 years; (5) The region affected by the change of NP include the north of Hetao in Inner Mongolian and the south area of Shanxi, where this situation will have the influence to the future diversion works' construction and its operation. 4. Analysis of wetness and dryness of the climate: (1) As a reconstruction method of drought indicators, Standardized Precipitation Index (SPI) is applicable as indicators of climate change monitoring in Northwest China; (2) The change of drought frequency is corresponding to the trend of precipitation. That is, to some extent, climate change mitigate the frequency of drought in the northern part of Xinjiang and western Qinghai, but increase the drought frequency in the central and southern region of Shaanxi and southeasten part of Gansu; (3) Relative to the climate change, Frequency of drought has a general downward trend in the whole region of Northwest China, despite the location is continuing to change.5. Analysis of the responses of hydrological elements to climate change: (1) The NP in northeast part of Northwest China is more vulnerable to climate change than that in west part of Qinghai and the eastern section of the Tianshan Mountains in Xinjiang, and this situation caused the NP increase in these region in future. The NP is not as vulnerable as that in other district of Northwest China; (2) Mean monthly T and P have a synergetic effect to the contemporaneous NP, so it is not comprehensive to analyze the response of temperature or precipitation to water resources system; (3) In different climatic zones, the extent of impact of mean monthly temperature and precipitation to the hydrological factors is different. T is a main impact factor to hydrological factors in the arid inland regions, desert margins and large irrigation district, and precipitation plays an important role in the semi-arid areas. P becomes to a relatively strong factors to hydrological factors in the higher elevation areas. Temperature's impact to hydrological factors is not obvious in the relatively moist regions in the southeast part of Northwest China. For the NP, Precipitation is the main factor in Northwest China. (4) The impact of mean annual T is weaker than tnat of P on hydrological factors. The NP is affected by P more than T. The trend of precipitation is a main factor to the impact on water resources system in the future. (5) After analysis of sensentivity of runoff in the Taohe River Basin and upstream of Heihe River, the result show that the T has small effect on surface runoff than P. The increase of T results in decrease of runoff and P affects the runoff singnificantly. The effect of climate change on groundwater table is due to the increase of evaporation after T increasing.