ORCHIDEE-ROUTING: A new river routing scheme using a high resolution hydrological database

Abstract

Abstract.This study presents a revised river routing scheme (RRS) for the Organising Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) land surface model. The revision is carried out to benefit from the high resolution topography provided the Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales (HydroSHEDS), processed to a resolution of approximately 1 kilometer. The RRS scheme of the ORCHIDEE uses a unit-to-unit routing concept which allows 5 to preserve as much of the hydrological information of the HydroSHEDS as the user requires. The evaluation focuses on 12 rivers of contrasted size and climate which contribute freshwater to the Mediterranean Sea. First, the numerical aspect of the new RRS is investigated, to identify the practical configuration offering the best trade-off between computational cost and simulation quality for ensuing validations. Second, the performance of the revised scheme is evaluated against observations at both monthly and daily timescales. The new RRS captures satisfactorily the seasonal variability of river discharges, although im-10 portant biases come from the water budget simulated by the ORCHIDEE model. The results highlight that realistic streamflow simulations require accurate precipitation forcing data and a precise river catchment description over a wide range of scales, as permitted by the new RRS. Detailed analyses at the daily timescale show promising performances of this high resolution RRS for replicating river flow variation at various frequencies. Eventually, this RRS is well adapted for further developments in the ORCHIDEE land surface model to assess anthropogenic impacts on river processes (e.g. damming for irrigation operation).

Assimilation of river discharge in a land surface model to improve estimates of the continental water cycles

“…The residence times are determined by multiplying a constant reservoir factor (g) with a slope index (k). The g for stream, overland and groundwater reservoirs are 0.24, 3 and 25 days km −1 , respectively (Ngo-Duc et al, 2007). The slope index is a function of distance (d) and slope (S) between a pixel and its downstream pixel (k = d/S 1/2 defined by Ducharne et al, 2003).…”

“…River discharge is an essential component of the earth's water cycles, which can be used as an indicator of the hydrological cycle intensification (Munier et al, 2012). It is important not only for water resources management, climate studies and ecosystem health over land (Syed et al, 2010;Sichangi et al, 2016) but also for providing freshwater inflow to ocean (Dai and Trenberth, 2002).…”

“…(e.g., the southern shores of the Mediterranean). Second, there are large discrepancies among models resulting from the differences in model inputs, parameterizations and atmospheric forcing data (Ngo-Duc et al, 2007;Wang et al, 2016;Liu et al, 2017).…”

“…This will allow us to compensate for model systematic errors or missing processes and provide estimates of the riverine input into the sea at high temporal and spatial resolutions. Although previous works exist on assimilation of river discharge (e.g., Li et al, 2015;Bauer-Gottwein et al, 2015;Pauwels and De Lannoy, 2009), these studies mainly focus on the stream flow prediction over individual catchments. They are difficult to extend to long-term timescales and large catchments due to the observations and computing time limitations.…”

Understanding the water cycle over the upper Tarim Basin: retrospecting the estimated discharge bias to atmospheric variables and model structure

“…Code and data availability. The land surface model is free to download on the website https://forge.ipsl.jussieu.fr/orchidee/ browser/branches/publications/ORCHIDEE_gmd-2018-57 (Nguyen-Quang et al, 2018). The WFD dataset can be obtained from http://www.waterandclimatechange.eu/about/ watch-forcing-data-20th-century (Weedon et al, 2010).…”