Northwestern China has an extremely complex climate due to the varied terrain and complexities of climate change where the environment is sensitive to both regional and global climate change. We employed the Mann-Kendal test to investigate trends of precipitation distributions using annual, seasonal, and monthly data records from 1960 to 2008. On the whole, the variations in precipitation patterns are more complex than those for temperature. The trends of annual, seasonal, and monthly precipitation have shown remarkable differences between the east and west. In the west such as in northern Xinjiang and western Qinghai, the variation is a significant increase, consistent with the temperature change, whereas in the east such as in eastern Gansu, and southern Shaanxi, the variation is a remarkable decrease, opposite to the change observed in temperatures.
The climate warming trend has been well documented at many locations around the world during the last several decades. This trend is projected to accelerate in the future and has great implications for hydrological cycle and water resources planning [
Precipitation is one of the most important indicators of the availability of water resources in a region. Changes to precipitation due to, for example, climate change, may vary greatly from region to region [
The aim of this study is to examine long-term trends of precipitation using the Mann-Kendall trend test [
The present study focuses on northwestern China, covering the provinces of Shaanxi, Gansu, and Qinghai, the autonomous regions of Ningxia and Xinjiang, and a portion of Inner Mongolia (Figure
Locations of temperature and precipitation recording stations in northwestern China.
To investigate the general trends in climatic conditions for locations in Northwest China, monthly temperature and precipitation data records for 1960–2008 from 204 stations (Figure
The time series of temperature and precipitation were analyzed using the Mann-Kendall nonparametric trend test. This test enables the investigation of long-term precipitation tendencies, without assuming that a given dataset follows a normal distribution.
The Mann-Kendall test was applied to annual, seasonal, and monthly precipitation data. The test statistic,
With the null hypothesis that
The standardized test statistic,
A nonparametric robust estimate of the magnitude of the slope of linear trend,
To support the analysis of annual, seasonal, and monthly precipitation trends, the precipitation concentration index was first calculated on a monthly basis for each station. The distribution of the precipitation concentration indices provides insight into regional heterogeneities in precipitation trends. On the whole, annual precipitation was affected much more by variations in monthly precipitation in regions including most of Xinjiang, Qinghai, western Gansu, and Inner Mongolia. In contrast, annual precipitation was affected most by variations of seasonal precipitation in locations such as Altay in Xinjiang, southeast of Gansu, and Shaanxi.
Due to topography, elevation, and other factors, the annual mean precipitation change is not consistent with annual mean temperature changes. Figure
Spatial distribution of
The distribution of seasonal precipitation is generally concentrated in spring, summer, and fall, accounting for 20%, 40%, and 35%, respectively, whereas only 5% annual precipitation arrives in the winter. Thus, variations of the seasonal precipitation in spring, summer, and fall can affect the annual precipitation in the study area significantly. Through
Spatial distribution of
Variations in monthly precipitation have obvious direct impact on seasonal and annual precipitation. So, the same spatial analysis was carried out using monthly precipitation figures. The result shows the two most remarkable months, which have the most significant variation. The precipitation trend in most regions has increased in July, generally in excess of 5 mm per decade; for example, observe most of Xinjiang and north and central Qinghai. Contrasting this, precipitation trends in most regions show a decrease in September, for example, northern Xinjiang, southern Qinghai and Ningxia, eastern Gansu, and Shaanxi, where the largest decrease is below −13 mm per decade, for example, in northern Shaanxi.
The aim of this study has been to catalog the spatial distribution of precipitation trends in Northwest China during 1960–2008. The results have shown that the spatial distribution of annual mean precipitation has clearly changed over nearly the last 50 years. Elevation has had a remarkable influence on temperature, whereas precipitation has been affected significantly by topography, hydraulic transport, and geographic position. The trends of annual, seasonal, and monthly precipitation appear to be distinctly polarized by geography; in the west, the increasing trend is significant, and in the east, a remarkable decrease is found. Thus, the trends of temperature and precipitation show a weak positive correlation in parts of Northwest China such as Xinjiang and Qinghai and a negative correlation in regions such as eastern Gansu, Shaanxi, and southern Ningxia.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors are grateful to the two anonymous reviewers for their very useful suggestions and comments. This study was supported by Major National Science Research Program (973 Program) (no. 2013CBA01806), the National Natural Science Foundation of China (41361013 and 31300388), State Key Laboratory of Cryosphere Open Fund (SKLCS 2012-10), and Lanzhou City University Ph.D. Research Fund (LZCU-BS2013-09 and LZCU-BS2013-12).