Elaboration of 3D Soil Hydraulic Databases in Hungary

Spatially detailed quantitative data regarding soil hydraulic properties is in high demand for a range of modeling applications. EU-SoilHydroGrids has demonstrated its utility at the European level, contributing to ecological forecasts, geological and hydrological hazard evaluations, and agri-environmental modeling, among other studies. Building on this continental precedent, comparable but larger-scale, 3D soil hydraulic databases have been targeted within the frame of National Laboratory for Water Science and Water Safety to be utilized at national and regional/watershed level in Hungary. First, HU-SoilHydroGrids, has been developed for the whole area of the country at 100 m spatial resolution with several enhancements (compared to EU-SoilHydroGrids) in its elaboration process.Pedotransfer functions (PTFs) were developed using advanced machine learning techniques, both independently and as part of ensemble models. These models were trained using the national soil hydrophysical dataset called MARTHA (acronym for Hungarian Detailed Soil Hydrophysical Database), ensuring the derivation of region-specific PTFs. The set of predictors utilized in the PTFs was augmented by additional environmental variables with comprehensive spatial coverage, including DEM-derived geomorphometric indices, climatic parameters, OE provided surface reflectance and derived data products, LULC. To spatially apply the resulting models, 100 m resolution information on primary soil properties was obtained from DOSoReMI.hu (Digital Optimized Soil Related Maps and Spatial Information in Hungary). Finally, based on a detailed accuracy assessment, the spatial predictions (map products) were complemented with co-layers representing the 5% and 95% quantiles. HU-SoilHydroGrids provides nationwide information on the most frequently required soil hydraulic properties (water content at saturation, field capacity and wilting point, saturated hydraulic conductivity and van Genuchten parameters for the description of the moisture retention curve) at a spatial resolution of 100 meters, down to 2 meters soil depth for six GSM standard layers. In comparison to EU-SoilHydroGrids, the description of soil moisture retention curves and hydraulic conductivity has significantly reduced squared error in the case of HU-SoilHydroGrids.A further step toward larger spatial resolution is based on NATASA (Hungarian acronym for Profile-level Database of Hungarian Large-Scale Soil Mapping) initiative for the conservation and digital processing of the still available soil observation legacy data originating from large-scale surveys carried out in Hungary between the 60s and 90s. Digitization of the soil observation records is in progress, firstly concentrating on the watershed of the Lake Balaton. The partly processed area contains already almost 37.000 soil observations in the three counties neighbouring the lake, which will be used in digital mapping of primary soil properties at a scale of 25 meters. These DSM products then will be similarly adapted as the 100 m resolution DOSoReMI.hu products for the derivation of soil hydraulic property predictions down to 2 meters for six standard GSM soil depth layers, thus providing watershed-level, large-scale 3D Soil Hydraulic Databases (LS-HU-SoilHydroGrids). Acknowledgement: This work has been carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF 2.3.1 21 2022 00008 project and the Sustainable Development and Technologies National Programme of the Hungarian Academy of Sciences (FFT NP FTA).