2020 Volume 50 Issue 2 Pages 85-94
Monthly precipitation sampling for stable isotopes (δ2H, δ18O) has been undertaken since 2005 in Miyakonojo City of southern Japan to investigate their seasonal variability and controlling factors. Long-term monthly mean precipitation values are higher than 250 mm in the rainy season (June–September) and lower than 200 mm in the non-rainy season (October–May). Monthly mean δ18O values are lower than and higher than −7‰ in rainy and non-rainy seasons, except for August. Likewise, monthly mean δ2H values are lower than and higher than −40‰ in rainy and non-rainy seasons. Monthly mean d-excess values are lower than and higher than 15‰ in warm (April–October) and cold (November–March) seasons, showing a strong negative correlation with monthly mean temperature. A negative correlation occurs between monthly isotopic compositions and monthly precipitation amounts over the entire year, with effects on δ18O and δ2H of −0.29‰/100 mm and −3.86‰/100 mm. A positive correlation occurs between monthly isotopic compositions and monthly temperatures only in the non-rainy season, with effects on δ18O and δ2H of 0.42‰/°C and 2.98‰/°C. Slopes and intercepts of Local Meteoric Water Lines ranged from 8.30 to 8.67 and from 12.85 to 22.07, yielding slopes close the Global Meteoric Water Line, but with much higher intercepts.
