Abstract:

Atmospheric precipitation is considered an important hydrological resource in arid and semiarid areas because it can recharge runoff and affect the spatial and temporal distribution of regional water resources, which in turn affect the regional ecological environment. Temperature is considered to affect many aspects of the region’s water cycle, ecology, and vegetation. However, few studies have been conducted on the trend analysis of precipitation and temperature in steppe watersheds. Therefore, the main purpose of this article is to determine the precipitation and temperature trends in a semiarid steppe watershed of north China (the Xilinhe River Basin located in Inner Mongolia). Using the gridded monthly precipitation data of the China Meteorological Data Service Centre and the daily temperature data of the Xilinhot Meteorological Station, we used the cumulative anomaly method to briefly analyze the variation characteristics of precipitation and the average temperature in the basin. Further, the innovative trend analysis (ITA) and innovative trend analysis-change boxes (ITA-CB) methods were used to detect precipitation and temperature trends in the selected area. The results showed that precipitation in the Xilinhe River Basin was unevenly distributed, with significant annual seasonal characteristics and interannual strong undulation. Precipitation in a year was mainly concentrated in summer and autumn (about 83.1% of the total annual value). Precipitation was less during 1961—1973, increased significantly during 1990—1998, decreased significantly during 1999—2011, and was close to or greater than the average level after 2012. The average temperature of the basin had a large difference in winter and a small difference in summer; it decreased from 1961 to 1987 and increased from 1988 to 2016. The results also showed that the annual precipitation presented a decreasing trend during the recent 56 years (1961—2016). On a seasonal scale, there was an increasing precipitation trend in winter and spring and a decreasing trend in summer and autumn. In particular, precipitation in winter rose significantly and steadily compared with that in spring. For precipitation in summer, its high-value areas showed an increasingly upward trend, and its low-value areas showed an increasingly downward trend. Thus, the possibility of extreme weather becomes greater. In autumn, the average change rate of precipitation decline was small, and there was an increasing trend in the low- and high-value areas. Although the increasing trend of precipitation in winter and spring was significant, it had little effect on the change in total precipitation for the whole year because of its limited total amount. With 1987 as the turning point, overall, the average temperature first fell and then rose on an annual scale. The results of ITA and ITA-CB further reflected that the overall increasing trend of the average annual temperature in 56 years was slowing down. The average temperature rise rate in spring and autumn was greater than that in summer and winter. During the coldest winter of the year, the average temperature rose at an accelerating rate. On the contrary, the temperature rise slowed down during the hottest summer. Therefore, it could be concluded that the temperature difference between seasons showed a decreasing trend.

Key words: innovative trend analysis (ITA), innovative trend analysis-change boxes (ITA-CB), trend, Xilinhe River Basin, precipitation, average temperature