Scholarly record
SPATIAL ANALYSIS OF MAXIMUM RUNOFF PROBABILITIES IN BULGARIA: A COMBINED APPROACH USING ERA5 AND LAND SURFACE MODELING
Abstract
This article presents a reproducible workflow for deriving gridded total runoff threshold layers for Bulgaria and the adjacent regional domain. ERA5-Land hourly runoff for 1981-2025 was first converted from accumulated fields to hourly increments following the ERA5-Land accumulation convention [4][7]. Annual maxima were then derived for 1 h, 3 h, 6 h and 24 h totals, and fixed annual exceedance probability (AEP) return levels were estimated for 1% and 5%. The fine resolution product uses D(Q) downscaling: return levels estimated on the native ERA5-Land grid are redistributed to an approximately 2 km grid by physically interpretable weights. SURFEX is used as a process-oriented land surface modelling with in-situ measurements reference for the focused 2013-2025 period, not as hydrometric validation. The resulting layers are suitable for regional threshold screening, GIS analysis and the design of preliminary runoff warning indicators, provided that their model origin and limitations are retained.
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References7
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