近44年来我国西北地区干湿特征分析

Aridity-wetness Characteristics over Northwest China in Recent 44 Years

利用我国西北地区1960—2003年131个测站降水和小型蒸发皿蒸发量资料,综合考虑降水和蒸发这两个水分平衡最关键的分量构造了降水蒸发均一化干湿指数,进而研究了西北地区干湿的时空演变特征。结果表明:一致性异常是西北地区近44年干湿特征的最主要空间分布模态;西北地区干湿异常特征主要分为西风带气候区型,高原气候区型和季风气候区型;整个西北地区及其西风带气候区、高原气候区年干湿特征呈较为显著的变湿趋势,大约在20世纪70年代中期均发生了由干向湿的突变,而季风气候区表现为变干趋势,并且在90年代前期发生了由湿向干的突变;整个西北地区及各分区近44年来主要以年代际周期振荡为主。

Northwest（NW） China covers Xinjiang, Qinghai, Ningxia, Shaanxi and the western part of Inner Mongolia; it is located to the north and northeast of the Qinghai-Tibetan Plateau, far away from oceans. This extensive region is one of the aridest areas in the world and also a principal arid and semi-arid expanse in China, including totally 85 % of such land in China. This region is under the impacts of westerly, plateau and monsoon climates so that rainfall undergoes great variability and there is a high frequency of drought, serving as a zone sensitive to climate change and ecologically vulnerable. The inference is presented by Shi Yafeng that the NW climate is changing from a dry, warm one to a moist, warm stage one, which is awaited for further studies with more climate elements. Whether climate pattern changes or not depends completely on the change in hydrological cycle whose critical ingredient is evaporation, by which, in combination with rainfall and runoff, a regional hydrological equilibrium is determined. Rainfall is focused on by previous studies on NW China climate change and the pattern conversion and it is considered by few researchers whether the climate is changing from a warm, dry one to a warm, moist pattern by means of rainfall and evaporation in combination, which are two no negligible aspects of water equilibrium on a regional basis. It is apparent that drought is led to by deficient precipitation and evaporation would increase such that it is feasible to take into account the budget of rainfall and precipitation in the study on transformation of arid-moist climate for the NW China, which is of far-reaching strategic and prac- tical significance to NW China socio-economic development. Based on 1960--2003 rainfall and small-sized evapo ration pan measurements from 131 stations in NW China, an aridity-wetness homogenized index of rainfall and evaporation is proposed as the crucial components of hydrological equilibrium, with EOF, REOF, tendency analysis, M-K sudden change check and Morlet wavelet analysis, the aridity-wetness evolution characteristic is analyzed over northwest China in recent 44 years. Results show that a regional consistent anomaly serves as the paramount mode of the 1960-2003 yearly dry and wet features, as well as the opposite feature in the NW （NE） to the SE （SW） which is also the important mode for the annual dry and wet abnormality. The space patterns for the arid and moist anomaly include the westerly, tableland and monsoon climates. The annual arid and wet features display greatly humidification trends in the whole NW, westerly and tableland climate zones, with the westerly climate humidification stronger than the trend of the tableland sub-zone, their abrupt change is from arid to moist in the mid-1970s. While the area on the fringe of monsoon climate in the southeast of NW China shows a trend of turning aridity, their abrupt change is from moist to arid in the early 1990s. In spite of the pe- riod surge which is not the same as in NW and three key climate zones, inter-decadal oscillation of over 8-year is a main period in all regions, 3-5-year inter-annual surge is also shown in all regions, but the intensity of amplitude is weak.