Spatial distribution and temporal trends of extreme temperature and precipitation events on the Loess Plateau of China during 1961-2007

Authors: LI, ZHI - Northwest Agricultural & Forestry University; ZHENG, FENLI - Northwest Agricultural & Forestry University; LIU, WENZHAO - Northwest Agricultural & Forestry University; Flanagan, Dennis

Submitted to: International Union for Quaternary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2010
Publication Date: 10/15/2010
Citation: Li, Z., Zheng, F., Liu, W., Flanagan, D.C. 2010. Spatial distribution and temporal trends of extreme temperature and precipitation events on the Loess Plateau of China during 1961-2007. International Union for Quaternary Research. 226(2010):92-100.

Interpretive Summary: Weather, including air temperatures and amount of rainfall, in some locations has been changing over the past 50 years, as a result of overall global warming. While average temperatures or rainfall may change somewhat, the occurrence of extreme climate events may experience greater changes. Extreme climate events, such as high temperatures, heat waves, frost days, and very large intense rain storms can have large impacts on both agriculture and the environment. For example, extended high temperatures can damage crops and decrease yields, while large intense rainfall can result in large runoff, high soil erosion, sediment yield, and flooding. In this paper we used 47 years of observed weather data from 50 weather stations across the Loess Plateau of China to determine if extreme climate events have been changing (increasing or decreasing). This was done by using the data to assess change in a number of indicator variables (heavy rainfall threshold, greatest 5-day total rainfall, simple daily rainfall intensity, longest dry period, heavy rainfall days, hot-day threshold, cold-night threshold, number of frost days, and longest heatwave). The information from 1961 to 1990 was used as the base period and averages computed, and then values from 1991 to 2007 were compared to these base period averages. Overall, we found that in general there was little noticeable change in the extreme precipitation events from 1960 to 2007. However, there was significant change in the extreme temperature events, with indicators at most station locations showing that temperatures and extreme temperatures and time periods had increased. These research findings impact other scientists as well as agency personnel assessing impacts of global climate change on regional environmental and agricultural systems. The techniques used here could also be applied to other locations around the world. Where large changes in extreme events are indicated, forward planning needs to be conducted to adapt agricultural systems to minimize negative impacts on productivity and the environment.

Technical Abstract: Extreme climate events often cause catastrophic damage to nature and human society. Therefore, regional assessments in various climate and geographic regions are needed for understanding the uncertainties in the changing trends for extreme climate events. The objective of this study was to assess the spatial distribution and temporal trends of extreme precipitation and temperature events in the Loess Plateau of China during 1961-2007. Nine indicators (pq90, px5d, pint, pxcdd, pnl9, txq90, tnq10, tnfd, txhw90) were chosen to quantify extreme climate events, the Mann-Kendall method and linear trend analysis were used to test the change in trend and the magnitude, and inverse distance weighted interpolation was used to interpolate the spatial patterns. Results showed that the most extreme climate indicators were spatially distributed with obvious gradients from the southeast to the northwest. Heavy rain threshold (pq90), greatest 5-day total rainfall (px5d), heavy rainfall days (pnl9), and cold-night threshold (tnq10) decreased from the southeast to the northwest, while simple daily rainfall intensity (pint), longest dry period (pxcdd) and number of frost days (tnfd) increased from the southeast to the northwest. Most stations had monotonic trends in extreme indicators during 1961-2007. However, the number of stations with significant trends varied greatly. Precipitation-based indicators showed more mixed patterns of change and few stations had significant trends. However, temperature-based indicators had more uniform changes and most stations had significant trends. Hot-day threshold (txq90) and cold-night threshold (tnq10), and the longest heatwave (txhw90) tended to increase while the number of frost days decreased since the 1960s on the Loess Plateau. Overall, extreme precipitation events did not change significantly; however, extreme temperature events became more severe and frequent. These results implied that extreme climate events on the Loess Plateau will continue to have adverse impacts, and adaptive measures should be considered for future ecological construction and agriculturally sustainable development.