Data on stable isotopic composition of δ18O and δ2H in precipitation in the Varaždin area, NW Croatia

The dataset in this article consists of one year of monthly observations of water stable isotopes in precipitation (July 2019 - May 2020). The samples were collected by rain gauge installed in the Hrašćica village in the Varaždin area, NW Croatia. The data presented in the article are raw isotope data of precipitation supplemented by calculated d-excess values, and local meteoric water lines (LMWL). The measured data is an extension to previous two year investigations (June 2017 – June 2019), which was published in the research article “Application of Stable Water Isotopes to Improve Conceptual Model of Alluvial Aquifer in the Varaždin Area” [1]. Local meteoric water lines (LMWL) are calculated for the entire period for which isotope analyses exist (June 2017 - May 2020). Presented data can be used as a background for investigation of precipitation, groundwater and surface water origin and their interrelationships.


a b s t r a c t
The dataset in this article consists of one year of monthly observations of water stable isotopes in precipitation (July 2019 -May 2020). The samples were collected by rain gauge installed in the Hrašćica village in the Varaždin area, NW Croatia. The data presented in the article are raw isotope data of precipitation supplemented by calculated d -excess values, and local meteoric water lines (LMWL). The measured data is an extension to previous two year investigations (June 2017 -June 2019), which was published in the research article "Application of Stable Water Isotopes to Improve Conceptual Model of Alluvial Aquifer in the Varaždin Area" [1] . Local meteoric water lines (LMWL) are calculated for the entire period for which isotope analyses exist (June 2017 -May 2020). Presented data can be used as a background for investigation of precipitation, groundwater and surface water origin and their interrelationships.
© 2020 The Author(s

Value of the Data
• Presented data provide an insight into seasonality of stable isotope ratios in precipitation, which is highly important component of the hydrological cycle, and associated local meteoric water lines serve as background for determination of the groundwater and/or surface water origin. In addition, the relationship between ratios δ 18 O, δ 2 H, and d-excess enables the determination of air masses from which the rainfall originates [1] . • Researchers working on hydrology/hydrogeology related problems can use the data for identifying the origin of precipitation, groundwater and surface water and determination of their interrelationships. • The data can be used as input for regional studies, e.g. investigation of isotope effects (seasonal, altitude, continental effect) in modern precipitation [3] .

Data Description
The data presented include water stable isotope ratios ( δ 18      isotope diagram, together with calculated local meteoric water lines and their equations ( Fig. 2 ). The calculated LMWL for the period from June 2017 to May 2020 is:

Experimental Design, Materials and Methods
Monthly composite precipitation samples ( N = 10) were collected using by a special designed rain gauge for collection of precipitation samples for stable isotope analysis, which was installed in the village Hrašćica (46.32516 °N, 16.29311 °E, 177 m a.s.l), near the town Varaždin -Varaždin County, NW Croatia. Field sampling was conducted on a monthly basis in duration of one year, from July 2019 to May 2020. The special designed rain gauge (which is used by IAEA) collected precipitation into 3 L HDPE container which is installed in the gauge. The last day of the month, composite sample was poured into 10 0 0 mL or in smaller or bigger HDPE plastic bottles with a tight-fitting cap (depending on how much sample was collected during the month), and preserved at 4 °C in the portable refrigerator until analysis. To remove impurities, all samples were filtered through 0.45 μm sterile syringe filters (Chromafil Xtra PET-45/25) before isotope analyses. Analyses were done upon arrival of the sample into the laboratory.