title: Precipitation isoscapes for New Zealand: enhanced temporal detail using precipitation-weighted daily climatology.
abstract: Predictive understanding of precipitation δ(2)H and δ(18)O in New Zealand faces unique challenges, including high spatial variability in precipitation amounts, alternation between subtropical and sub-Antarctic precipitation sources, and a compressed latitudinal range of 34 to 47 °S. To map the precipitation isotope ratios across New Zealand, three years of integrated monthly precipitation samples were acquired from >50 stations. Conventional mean-annual precipitation δ(2)H and δ(18)O maps were produced by regressions using geographic and annual climate variables. Incomplete data and short-term variation in climate and precipitation sources limited the utility of this approach. We overcome these difficulties by calculating precipitation-weighted monthly climate parameters using national 5-km-gridded daily climate data. This data plus geographic variables were regressed to predict δ(2)H, δ(18)O, and d-excess at all sites. The procedure yields statistically-valid predictions of the isotope composition of precipitation (long-term average root mean square error (RMSE) for δ(18)O = 0.6 ‰; δ(2)H = 5.5 ‰); and monthly RMSE δ(18)O = 1.9 ‰, δ(2)H = 16 ‰. This approach has substantial benefits for studies that require the isotope composition of precipitation during specific time intervals, and may be further improved by comparison to daily and event-based precipitation samples as well as the use of back-trajectory calculations.
authors.affiliation: a National Isotope Centre , GNS Science , Lower Hutt , New Zealand.
authors.forename: W Troy
authors.initials: WT
authors.lastname: Baisden
authors.affiliation: a National Isotope Centre , GNS Science , Lower Hutt , New Zealand.
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Keller
authors.affiliation: b Department of Chemistry , Otago University , Dunedin , New Zealand.
authors.forename: Robert
authors.initials: R
authors.lastname: Van Hale
authors.affiliation: b Department of Chemistry , Otago University , Dunedin , New Zealand.
authors.forename: Russell D
authors.initials: RD
authors.lastname: Frew
authors.affiliation: c Isotope Hydrology Laboratory , International Atomic Energy Agency , Vienna , Austria.
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Wassenaar
mesh_terms: D002980:Climate; D003903:Deuterium / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D055904:Meteorology; D008962:Models, Theoretical; D009520:New Zealand; D010103:Oxygen Isotopes / Q000032:analysis; D011891:Rain / Q000737:chemistry*; D012621:Seasons; D012914:Snow / Q000737:chemistry*
chemical_list: D010103:Oxygen Isotopes; D003903:Deuterium
keywords: Hydrogen-2; New Zealand; isoscapes; isotope hydrology; oxygen-18; precipitation; spatial depiction