The Stable Isotope Characteristics of Precipitation in the Middle East Highlighting the Link between the Köppen Climate Classifications and the δ18O and δ2H Values of Precipitation

Abstract

The Middle East is faced with a water shortage crisis due to its semiarid and arid climate. In this paper, precipitation as an important part of the water cycle was evaluated in 43 stations across the Middle East using the stable isotope technique to study the parameters which influence the stable isotope content of precipitation. First, the stepwise regression model was applied to determine the main geographical and climatological factors affecting the stable isotopes in precipitation. Secondly, the stepwise model was also used to simulate the stable isotope values in precipitation. Furthermore, due to the notable climatic variations across the Middle East, the precipitation sampling stations were classified into six groups based on the Köppen climate zones. Significant variations in the stable isotope values of precipitation were observed in the stations of each climate zone. Finally, the Middle East meteoric water line was developed for the dry and wet periods based on the average stable isotopes in the studied stations. The developed lines showed a lower slope compared to the GMWL due to the higher air temperature and relative humidity in the Middle East compared to the average global conditions. To conclude, the stable isotope contents in precipitation showed significant temporal and spatial variations due to the notable climatic variations across the Middle East.

Stable isotope composition in precipitation and groundwater of Shwan Sub-Basin, Kirkuk governorate, northeast of Iraq

“…The high isotope composition (δ 2 H and δ 18 O) in precipitation of the study area gives good agreement with the high values observed in eastern tropical Africa and the Arabian Peninsula in previous studies (Leng 2006;Michelsen et al 2015;Heydarizad et al 2021). This indicates the climate conditions in these regions have a great influence on stable isotopes values in precipitation.…”

Stable Isotope Signatures in Tehran’s Precipitation: Insights from Artificial Neural Networks, Stepwise Regression, Wavelet Coherence, and Ensemble Machine Learning Approaches

“…It is the most populous metropolitan area in West Asia, and the Middle East's most populous metropolitan area (Figure 1a). The Köppen climate classification places Tehran in the BSk group with a cold se arid climate [24]. Tehran's climate is heavily influenced by the geographic features t separate the city's northern (Alborz Mountains) and southern (central desert) halv Mount Damavand located near Tehran, has the highest elevation in Iran and even Middle East region.…”

“…During the cold period (November to April), the monthly precipitat amount showed higher values, while the water vapour pressure and air temperat showed lower values, compared to the warm period (May to October) of the year. T The Köppen climate classification places Tehran in the BSk group with a cold semiarid climate [24]. Tehran's climate is heavily influenced by the geographic features that separate the city's northern (Alborz Mountains) and southern (central desert) halves.…”

“…Several models were developed, including stepwise regression, ANNs (including DNN and SNN), XGBoost, and RF. Stepwise modelling is a useful tool for developing statistical models that accurately predict outcomes or responses while minimizing the number of predictors required [4,19,20,24]. This technique is used to choose the most suitable predictor variables for a multiple linear regression model, which is generally expressed as Equation ( 2):…”

“…They presented maps of the spatial distribution of 18 O, 2 H, and d-excess in precipitation across Iran using the stepwise technique [4]. Additionally, Heydarizad and colleagues developed a spatial distribution map of stable isotope signatures in precipitation across the Middle East using the stepwise model [24].…”