Conflicts of interest
This research was supported by an NSERC Discovery Grant held by Jan Adamowski.
As a basic meteorological variable, precipitation is an excellent indicator widely used in the fields of integrated water resources management, crop water requirements prediction, and ecological environment assessment. In the past century, global climate change (e.g., the significant increase in air temperature), which has greatly influenced the water circulation and hydrological processes (Garbrecht et al., 2004; Novotny and Stefan, 2007; IPCC, 2007), has drawn the attention of numerous researchers. In most regions, climate change indeed caused dramatic changes in precipitation (Liu et al., 2008; Chen and Chu, 2014; Zarch et al., 2015); however, the changing characteristics was quite different among regions. Several studies have indicated that precipitation generally presented an increasing trend in the Northern Hemisphere in the past several decades (Groisman et al., 2005; IPCC, 2007; Westra et al., 2013; Cao and Pan, 2014; Fan et al., 2014). The same trend has been found in most regions of China, including the western China, the Yangtze River basin, and the southeastern coast; however, precipitation has shown a decreasing trend over the north China and the Sichuan Basin (Zhai et al., 2005). Thus, it is necessary to investigate the spatial and temporal characteristics of precipitation for the designated region.
Specifically, the Three-River Headwaters (noted as TRH hereafter) region, a plateau mountainous region in the western China, is particularly sensitive to climate change, which may bring serious disturbances to the prostanoid receptors (Fan et al., 2010; Immerzeel et al., 2010; Zhang et al., 2013; Tong et al., 2014; Zhu et al., 2015). With reference to precipitation, Liang et al. (2013) reported an increasing trend in the annual precipitation across the TRH region during 1960–2009 using the observed data from 12 meteorological stations. Yi et al. (2013) reached a similar finding through analyzing the monthly data during 1961–2010; however, the seasonal precipitation presented the decreasing trends during the same period in some parts of the TRH region. Based on the observed data from 43 meteorological stations inside or around the TRH region, Tong et al. (2014) indicated that the annual precipitation generally showed an increasing trend from 1990 to 2012, and such trend was more obvious with significant fluctuations after 2004. Moreover, changes in precipitation extremes were investigated by using the daily data from 12 meteorological stations, and the results demonstrated that most of the selected indices exhibited the increasing trends during 1960–2012 (Cao and Pan, 2014).
It is worth noting that precipitation can be characterized by significant spatial variation for regions with large elevation variations (e.g., the TRH region in this study). Normally, the relationship between precipitation and elevation can be expressed by various functional forms, such as linear, logarithmic and exponential (e.g., Osborn, 1984; Daly et al., 1994; Naoum and Tsanis, 2004; Shi, 2013). Overall, the studies of the relationship between these two variables indicated that the dominant impact factor is the local climate. For example, precipitation may generally increase along with the increase of elevation in most regions, (e.g., Goovaerts, 2000; Chu, 2012); however, above a certain altitude, precipitation may decrease with elevation increase (e.g., Schermerhorn, 1967). Therefore, it is valuable to explore the relationship between precipitation and elevation. Moreover, precipitation can be influenced by a variety of related meteorological variables, such as air pressure, air temperature, wind speed, and so on (Singh, 1988; Benestad, 2013; Makarieva et al., 2014). In the past several decades, air temperature in the TRH region has presented a significant increasing trend (Liang et al., 2013), along with the global warming; and wind speed has been reducing worldwide (e.g., McVicar et al., 2008; Pryor et al., 2009). These meteorological variables may have great effects on the spatial and temporal characteristics of precipitation in the TRH region, which should be further studied.
Conflicts of interest