Abstract
Soil moisture is a key variable in the terrestrial water and energy system. This study presents an hourly index that provides soil moisture estimates on a high spatial and temporal resolution (1 km × 1 km). The long established Antecedent Precipitation Index (API) is extended with soil characteristic and temperature dependent loss functions. The Soilgrids and ERA5 data sets are used to provide the controlling variables. Precipitation as main driver is provided by the German weather radar data set RADOLAN. Empiric variables in the equations are fitted in a optimization effort using 23 in-situ soil moisture measurement stations from the Terrestial Environmental Observatories (TERENO) and a separately conducted field campaign. The volumetric soil moisture estimation results show error values of 3.45 Vol% mean ubRMSD between RADOLAN_API and station data with a high temporal accordance especially of soil moisture upsurge. Further potential of the improved API algorithm is shown with a per-station calibration of applied empirical variables. In addition, the RADOLAN_API data set was spatially compared to the ESA CCI soil moisture product where it altogether demonstrates good agreement. The resulting data set is provided as open access data.
Highlights
Soil moisture plays a key role in the interaction of different land surface processes and energy fluxes [1,2,3]
This study introduces the hourly weather radar data, temperature and soil information based soil moisture data set RADOLAN_API
The utilized empirical variables in the Antecedent Precipitation Index (API) formula are once optimized to be used in the spatial API data set RADOLAN_API, and on a per-station basis to evaluate the adjustability of the improved API algorithm to given specific circumstances concerning interplay of soil characteristics and natural surroundings
Summary
Soil moisture plays a key role in the interaction of different land surface processes and energy fluxes [1,2,3]. It controls processes like evaporation, infiltration and runoff, the fundamentals of the hydrological cycle [4,5]. Soil moisture influences hazards of different sorts, e.g., the extent or magnitude of floods [6]. Temperature or precipitation extremes relate to soil moisture state and memory [7]. Soil moisture further is the main governing resource in relation to ecosystem function and form as it provides water for nutrient uptake and transpiration [8].
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