Hydrological simulation of ungauged basins via forcing by large‐scale hydrology models

Abstract

The established watershed's hydrologic simulation process, involving the calibration and validation of a model through spatiotemporal streamflow observations, has recently been adapted to encompass ungauged watersheds. The research introduces a methodology for simulating ungauged hydrosystems, suggesting the calibration and validation of regional rainfall‐runoff models using large‐scale hydrological models (LSMs) in the absence of in situ streamflow measurements. For doing so, LSM's 30‐years simulated discharges at various basins and subbasins of the case study River Basin District are assessed for their accuracy against the limited available observations. Subsequently, the rectified time series tunes the optimal parametrization of a regional lumped hydrologic model that is triggered by precipitation and temperature data from a partially dense meteorological network. The validated regional model is then applied in selective ungauged neighbouring subbasins employing the regionalization concept used in LSMs, that is in basins with similar physiographic characteristics to those where the regional model was set up. The performance of the research is assessed using statistical metrics. In cases where observations are available, the results show very satisfactory indexes (e.g., coefficient of determination: 0.654 < R2 < 0.949, Kling‐Gupta efficiency: 0.759 < KGE <0.790, Nash–Sutcliffe efficiency: 0.649 < NSE <0.745 for all the cases). In completely ungauged basins and in an order of magnitude index, the comparison of the simulated discharges with those from the LSM also indicates the satisfactory performance of the proposed approach. To sum up, the methodology underscores the alternate use of large and regional scale hydrological modelling coupling as an asset across various basin scales globally, offering reliable water quantity information.

Large-Scale Hydrological Models and Transboundary River Basins

“…The literature indicates that only a very limited number of scholars have utilized and validated the performance of these models in Greece and in its international waters. For instance, Skoulikaris and Piliouras [9], and Skoulikaris [36], evaluated E-HYPE's performance solely for the Vardar/Axios river basin, while Mentzafou et al [61] used the specific model's simulated discharges as those that occur in seven national rivers, but without any validation. Notably, although LISFLOOD outputs form part of the EU Climate Data Store produced by the European Flood Awareness System (EFWS) as part of the Copernicus Programme [62], the model has yet to be utilized and evaluated in Greece.…”

“…Focusing on the two LSMs, although they are well-established and validated models, as clearly indicated in the Section 2, e.g., [9,35,41,42], none of the Greek national or international basin gauges, along with their relative gauges, have been utilized for validation during their development phase. Specifically, that of LISFLOOD uses only a station (out of the 693 utilized stations) in the upper part of the Struma basin for its validation [62], while E-HYPE validation does not include sub-Danubian basins [31].…”

“…The calibration of E-HYPE is based on numerous discharge stations, while independent stations are used for its validation [33]. The literature review demonstrates that the E-HYPE model has been reviewed and validated at various spatiotemporal scales [9,35,36].…”

“…However, WFD's primary aim is water quality rather than quantity issues, resulting in limited knowledge about the available river runoffs in several EU Member States. For instance, in Greece, the transboundary rivers and their tributaries are not regularly monitored, making them either completely or partially ungauged [9]. Moreover, and despite the emergence of spatiotemporal coverage from remote sensing water-related products, their validation and ground truth rely on observations [10,11].…”

“…The use of large-scale hydrological models (LSMs) is an emerging advancement in Earth system modeling and climate impact assessment [12], since they address water management challenges, such as global water security, by expanding the scope of modeling from the catchment scale to continental and global domains [13]. Initially designed for flood predictions and early warning systems across large geographical areas [14], LSMs have seen their utility expand to include long-term simulations across diverse environments when provided with relevant long-term input time series [9]. LSMs, much like traditional catchment-scale models, rely on a variety of input parameters, such as topographic characteristics, meteorological variables, and land uses, which are sourced from global datasets [15].…”