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The temperature effect

The temperature effect is predominantly rooted in the temperature dependence of isotopic fractionation during the condensation of precipitation and causes, for example, summer precipitation to exhibit higher δ18O values than winter precipitation (Clark and Fritz, 1997Craig, 1961Dansgaard, 1964Kohn and Welker, 2005Lee and Fung, 2008Mook, 2006Rozanski et al., 1993). The slope of the temperature effect varies geographically (Aggarwal et al., 2012Akers et al., 2017Dayem et al., 2010Gat, 2010Gourcy et al., 2005Sime et al., 2009) and seasonally (Akers et al., 2017Field, 2010Jacob and Sonntag, 1991Schmidt et al., 2005), but strong temperature effects and relatively consistent slopes are observed in many regions (Bowen, 2008Cole et al., 1999Field, 2010Kohn and Welker, 2005Noone et al., 2002Schmidt et al., 2005). At tropical latitudes, or other areas with temperatures consistently above 20°C, δ18O of precipitation decreases with increasing amounts of precipitation or high humidity at a set location (Dansgaard, 1964Rozanski et al., 1993). The amount effect is thought to be caused by reduced evaporation and equilibration in larger raindrops (Bony et al., 2008Dansgaard, 1964Risi et al., 2008Rozanski et al., 1993), increased relative humidity at the precipitation site (Araguás-Araguás et al., 2000Rozanski et al., 1993Salamalikis et al., 2016a) and recycling of re-evaporated moisture (Bony et al., 2008Cai et al., 2016Moore et al., 2014Risi et al., 2008). In monsoon regions, the amount effect may also partially be related to organised convection effects (Kurita, 2013Lekshmy et al., 2014Tharammal et al., 2017). The amount effect is most pronounced in coastal and island locations (Rozanski et al., 1993), in tropical regions and in areas characterised by monsoon activity, which creates a marked seasonal δ18Oprecip pattern (Aizen et al., 1996Araguás Araguás and Froehlich, 1998Liu et al., 2014Posmentier et al., 2004Vuille et al., 2005). Both temperature and amount effects are moderated by moisture source effects and by changes in atmospheric cycling