Can we use precipitation isotope outputs of isotopic general circulation models to improve hydrological modeling in large mountainous catchments on the Tibetan Plateau?

Abstract

Abstract. Issues related to large uncertainty and parameter equifinality have posed big challenges for hydrological modeling in cold regions where runoff generation processes are particularly complicated. Tracer-aided hydrological models that integrate the transportation and fractionation processes of water stable isotope are increasingly used to constrain parameter uncertainty and refine the parameterizations of specific hydrological processes in cold regions. However, the common unavailability of site sampling of spatially distributed precipitation isotopes hampers the practical applications of tracer-aided models in large-scale catchments. This study, taking the precipitation isotope data (isotopes-incorporated global spectral model – isoGSM) derived from the isotopic general circulation models (iGCMs) as an example, explored its utility in driving a tracer-aided hydrological model in the Yarlung Tsangpo River basin (YTR; around 2×105 km2, with a mean elevation of 4875 m) on the Tibetan Plateau (TP). The isoGSM product was firstly corrected based on the biases between gridded precipitation isotope estimates and the limited site sampling measurements. Model simulations driven by the corrected isoGSM data were then compared with those forced by spatially interpolated precipitation isotopes from site sampling measurements. Our results indicated that (1) spatial precipitation isotopes derived from the isoGSM data helped to reduce modeling uncertainty and improve parameter identifiability in a large mountainous catchment on the TP, compared to a calibration method using discharge and snow cover area fraction without any information on water isotopes; (2) model parameters estimated by the corrected isoGSM data presented higher transferability to nested subbasins and produced higher model performance in the validation period than that estimated by the interpolated precipitation isotope data from site sampling measurements; (3) model calibration forced by the corrected isoGSM data successfully rejected parameter sets that overestimated glacier melt contribution and gave more reliable contributions of runoff components, indicating the corrected isoGSM data served as a better choice to provide informative spatial precipitation isotope than the interpolated data from site sampling measurements at the macro scale. This work suggested plausible utility of combining isoGSM data with measurements, even from a sparse sampling network, in improving hydrological modeling in large high mountain basins.

Assessing the influence of water sampling strategy on the performance of tracer-aided hydrological modeling in a mountainous basin on the Tibetan Plateau

“…According to our previous evaluation of the isoGSM product, it overestimated precipitation δ 18 O in the YTR basin (Nan et al, 2021b). To correct bias in the isoGSM products, grab samples of precipitation were collected in the wet season of 2005 at four stations along the main channel of YTR, i.e., Nuxia (3691 m a.s.l.…”

“…REWs were extracted for the YTR basin and KR catchment, respectively (Tian et al, 2020;Nan et al, 2021aNan et al, , 2021b. Areal averages of the gridded estimates of meteorological variables, vegetation cover and soil property were calculated in each REW to drive the model.…”

“…Forced by the inputs of precipitation and glacier meltwater isotopic compositions, the model simulates the isotope evolution in all the water sources in the watershed, including stream water, soil water and snowpack. The iGCM isotope products properly corrected by δ 18 O measurements of precipitation samples have proved feasible to force the THREW-T model in large catchments like YTR on the TP (Nan et al, 2021b).…”

“…Tracer-aided hydrological models integrating environmental tracer (e.g., stable oxygen isotope, 18 O) modules into runoff generation processes have proved helpful for parameter calibration, model structure diagnosis and CRC quantification (Son and Sivapalan, 2007;Birkel et al, 2011), and are increasingly adopted in cold catchments (e.g., Ala-aho et al, 2017;He et al, 2019;Nan et al, 2021a). Recent researches indicated that estimates of precipitation δ 18 O from outputs of isotopic general circulation models (iGCMs) perform well on forcing traceraided models in large basins with a low cost of water sampling (Delavau et al, 2017;Nan et al 2021b). Similarly to the tracer-based end-member mixing methods that utilize the different tracer signatures of water sources to separate the hydrograph and quantify CRCs (Klaus and McDonnell, 2013;He et al, 2020), the tracer-aided hydrological models used the differed isotopic compositions of runoff components to constrain the water apportionments in runoff generation.…”

Validation and Bias Correction of Monthly δ18O Precipitation Time Series from ECHAM5-Wiso Model in Central Europe

“…The stable isotopic composition is expressed in δ-values (‰) with negative (positive) cases for isotopically depleted (enriched) samples. δ 18 O in precipitation is of principal importance in several hydrological, meteorological, and climatic applications. For a detailed description of the parameters and processes affecting 18 O/ 16 O ratio in precipitation, refer to [2,3].…”