Comparison of meteoric water lines at different temporal scales and regression methods in inland monsoon region, Northwest China.

The local meteoric water line (LMWL) is an important basis for tracing the regional hydrological processes with stable isotopes. The establishment of LMWL, which can represent the overall characteristics of stable isotopes of local precipitation, is crucial for accurately revealing the hydrological processes. The influences of different temporal scales and regression methods on the established LMWL were analyzed and compared based on nine years of stable isotopic data of precipitation in Changwu Tableland, a typical area of the inland monsoon region of Northwest China. The results showed that, for different regression methods, the LMWL established by stable isotopes of annual precipitation was basically stable, whereas the LWML established by each precipitation event and the monthly precipitation data showed significant differences with different regression methods. The LMWL from the ordinary least squares regression (OLSR), major axis regression (MA) and reduced major axis regression (RMA) methods were significantly different based on the data of precipitation event, monthly precipitation data, and annual precipitation data, respectively. Only when OLSR, MA and RMA considering precipitation weighting were used, the LMWL established by these scale data was relatively close. This suggested that special attention should be paid to the selection of precipitation stable isotope data scale and regression method when LMWL was established in areas with temporal heterogeneity of precipitation and stable isotopic characteristics. For regions where stable isotope observations of precipitation were difficult and data were limited, the precipitation weighted major axis regression or reduced major axis regression methods are recommended during the establishment of representative LMWL.

Anomalous stable hydrogen-oxygen isotope characteristics and water vapor sources of autumn precipitation in the Weihe River basin, Northwest China.

The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.