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Toward Locally Relevant Global Hydrological Simulations

HBV para­me­ters

Glob­al high-res­o­lu­tion para­me­ter maps for HBV

All hydro­log­i­cal mod­els are sim­pli­fi­ca­tions of a com­plex real­i­ty and there­fore need to be cal­i­brat­ed to obtain sat­is­fac­to­ry stream­flow sim­u­la­tions. Here we present high-res­o­lu­tion (0.05°) opti­mized para­me­ter maps for the con­cep­tu­al hydro­log­i­cal mod­el HBV cov­er­ing the entire land sur­face includ­ing ungauged regions.

Glob­al maps of four key HBV mod­el para­me­ters derived using the new region­al­iza­tion approach.

The maps were pro­duced using a nov­el para­me­ter region­al­iza­tion approach that involves the opti­miza­tion of trans­fer equa­tions link­ing mod­el para­me­ters to cli­mate and land­scape char­ac­ter­is­tics. The opti­miza­tion was per­formed in a ful­ly spa­tial­ly dis­trib­uted fash­ion at high res­o­lu­tion (0.05°), instead of at lumped catch­ment scale, using an unprece­dent­ed data­base of dai­ly observed stream­flow from 4229 small catch­ments world­wide.

Schemat­ic dia­gram illus­trat­ing the main steps of the mod­el para­me­ter region­al­iza­tion approach.

The region­al­ized para­me­ters result­ed in a medi­an Kling-Gup­ta Effi­cien­cy (KGE) improve­ment of +0.29 (rel­a­tive to uncal­i­brat­ed para­me­ters) in 4229 ful­ly inde­pen­dent val­i­da­tion catch­ments. Improve­ments were obtained for 88 % of the val­i­da­tion catch­ments. Sub­stan­tial improve­ments were obtained even for val­i­da­tion catch­ments locat­ed far from the catch­ments used for opti­miza­tion, under­scor­ing the val­ue of the derived para­me­ters for poor­ly gauged regions.

The improve­ment in Kling-Gup­ta Effi­cien­cy (KGE) using the region­al­ized para­me­ters rel­a­tive to uncal­i­brat­ed para­me­ters for 4229 inde­pen­dent val­i­da­tion catch­ments.

For more info see the fol­low­ing open-access pub­li­ca­tion:

Down­load

The lat­est ver­sion (0.8) of the para­me­ter maps, includ­ing the HBV mod­el code used to derive the maps, can be down­loaded here. If the dataset forms a key com­po­nent of your research, we kind­ly ask that you give us the oppor­tu­ni­ty to com­ment on your results pri­or to pub­li­ca­tion. The data and code are released under the CC BY-NC 4.0 license and thus may not be used for com­mer­cial pur­pos­es. By using the data in any pub­li­ca­tion you agree to cite the above-men­tioned paper. The out­dat­ed glob­al 0.5° para­me­ters maps for HBV described in Beck et al. (2016) are avail­able here.

Fre­quent­ly asked ques­tions

Can the para­me­ter maps be used for cli­mate change impact assess­ments?

Runoff pro­jec­tions pro­duced using HBV with region­al­ized para­me­ters are prob­a­bly in most cas­es more reli­able than those pro­duced using HBV with unop­ti­mized para­me­ters. The fol­low­ing caveats should, how­ev­er, be kept in mind. First, since the region­al­ized para­me­ters were opti­mized to pro­duce bet­ter runoff sim­u­la­tions, they do not nec­es­sar­i­ly rep­re­sent hydro­log­i­cal process­es more real­is­ti­cal­ly. Sec­ond­ly, the valid­i­ty of the region­al­ized para­me­ters, which were opti­mized using his­toric cli­mate con­di­tions, may be reduced when the future cli­mate con­di­tions are sig­nif­i­cant­ly dif­fer­ent. See Vaze et al. (2010) and Fowler et al. (2020) for fur­ther dis­cus­sion.

Which of the ten sets of glob­al para­me­ter maps should I use?

The ten sets of glob­al para­me­ter maps rep­re­sent dif­fer­ent cross-val­i­da­tion folds, mean­ing they were derived from slight­ly dif­fer­ent (but over­lap­ping) sub­sets of catch­ments. All ten sets of para­me­ter maps are equal­ly uncer­tain and there­fore should pro­duce equal­ly “good” sim­u­la­tions. Ide­al­ly, all ten sets of para­me­ter maps are used in an ensem­ble mod­el­ing frame­work to obtain an ensem­ble of out­puts, the spread of which pro­vides an indi­ca­tion of the uncer­tain­ty in the para­me­ters. See McIn­tyre et al. (2005) and Yang et al. (2011) for more dis­cus­sion on ensem­ble mod­el­ing.

Can I use the para­me­ter maps at anoth­er spa­tial res­o­lu­tion or only 0.05°?

The inter­ac­tions between mod­el para­me­ters and sim­u­la­tion results are gen­er­al­ly high­ly com­plex and non­lin­ear. The out­puts of a low-res­o­lu­tion mod­el with resam­pled para­me­ter maps will there­fore like­ly sig­nif­i­cant­ly dif­fer from the resam­pled out­puts of a high-res­o­lu­tion mod­el with 0.05° para­me­ter maps. Thus, we do not rec­om­mend using the para­me­ter maps at oth­er spa­tial res­o­lu­tions. See Beven (1995), Kling and Gup­ta (2009), and Fre­und et al. (2020) for fur­ther dis­cus­sion.

Acknowl­edge­ments

The para­me­ter maps were pro­duced by Hylke Beck (Prince­ton Uni­ver­si­ty). The fol­low­ing orga­ni­za­tions are thanked for pro­vid­ing stream­flow and/​or catch­ment bound­ary data: the Unit­ed States Geo­log­i­cal Sur­vey (USGS), the Glob­al Runoff Data Cen­tre (GRDC), the Brazil­ian Agen­cia Nacional de Aguas, EURO-FRIEND-Water, the Euro­pean Com­mis­sion Joint Research Cen­tre (JRC), the Water Sur­vey of Cana­da (WSC), the Aus­tralian Bureau of Mete­o­rol­o­gy (BoM), and the Chilean Cen­ter for Cli­mate and Resilience Research (CR2).

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