Environmental Engineering Reference
location with Alborz Mountains in its north and the central desert in the south. It can
be generally described as mild in spring and autumn, hot and dry in the summer, and
cold in the winter. As the city is large with significant differences in elevation for
various zones, the weather is often cooler in the hilly north than in the flat southern
part of Tehran. Average annual amount of precipitation recorded at the meteorologi-
cal station is approximately 227 mm. Monthly rainfall is strongly influenced by
season (month and moisture). The maximum and minimum recorded temperatures
are approximately 39 °C in July and −1 °C in January. Tehran's main moisture
source of precipitation is due to the Atlantic and the Eastern Mediterranean rain-
falls. It has 12 meteorological stations, where measurements of meteorological data
are available since 1951-2012.
New Delhi is located in the north of India (lat. 77°12′N; long. 28°36′E) with an
average elevation of 216 m above msl. New Delhi's version of a humid subtropical
climate is noticeably different from many other cities with this climate classifica-
tion. In other words, it features long and very hot summers, relatively dry and cool
winters, a monsoonal period, and dust storms. Summers are long, from early April
to October, with the monsoon season in the middle of summer. Winter starts in
November and peaks in January. New Delhi's highest temperature ever recorded is
47.2 °C, while the lowest recorded temperature is −0.6 °C. The average annual
rainfall is approximately 714 mm, most of which occurs during the monsoons in
July and August.
In the Tehran and New Delhi stations, precipitation samples were collected to moni-
tor oxygen, deuterium, and tritium isotopes in precipitation.
In Iran, precipitation samples were collected from 1960 to 1987 in Mehrabad
station located at 35.41°N, 51.19°E and 1,200 m above msl. Tehran has 12 meteo-
rological stations, among which Mehrabad meteorological station is the nearest one
to Tehran GNIP station.
Since 1960, 40 meteorological stations in India are monthly collecting precipita-
tion samples for the GNIP. The data has been derived from New Delhi station
(N:28.58°, E:77.7° and 212 m above msl). The isotope and meteorological data
have been recorded from 1960 to 2009 at New Delhi station.
This research contains two main initial objectives: firstly, the local meteoric
water lines (LMWLs) were derived by using regression models of these cities and
secondly, an investigation was conducted to examine the effects of variations in
temperature on oxygen isotope value (ʴ 18 O). The time-series variation of the ʴ 18 O,
ʴD and D-excess values of precipitation with the observed monthly amount of pre-
cipitation (mm) and temperature (°C), which were collected at the same time, are
presented in Table 1 (IAEA 2012 ).