Areal Drought Method

The Areal Drought Method provides forecasts of the area affected by drought, total drought duration of area in drought, and total deficit volume of area in drought based on precipitation, precipitation-evapotranspiration, soil moisture, groundwater, and runoff.

Description & Technical Information


The areal drought method gives a summary on the area affected by drought and its characteristic. Drought might cover the whole river basin affecting, for instance, groundwater, and river flow. Severe droughts usually have a transnational nature. Gridded time series from forecasted spatially-distributed drought indices are used as input to forecast the spatial behavior of drought in different variables, like precipitation, precipitation-evapotranspiration, soil moisture, groundwater, and runoff (Peters et al., 2006; Tallaksen et al., 2009; Corzo-Perez et al., 2011).

Outcome of the areal drought analysis is plotted as time series for the whole of Europe, regions, Pilot Sites, or as so-called Severity-Area-Frequency (SAF) curves. SAF curves present the relation between the severity e.g. areal deficit volume and the area in drought for various return periods (Hisdal and Tallaksen, 2003). Areal indices products give probabilistic forecasts of time series of areal indices for different variables (precipitation, precipitation-evapotranspiration, soil moisture, groundwater, and runoff). The specific areal drought indices are: (i) area in drought (percentage of grid cells in drought up to 7 months ahead), (ii) drought duration for 10th, 25th, 50th, 75th, and 90th percentiles for each ensemble member, and (iii) drought deficit volume for 10th, 25th, 50th, 75th, and 90th percentiles for each ensemble member. This will be done as seasonal forecasts for the standardized indices and the forecasts of the threshold indices; except for deficit volume only the threshold method is used.

In the area in drought, each grid cell represents a specific fraction u[i] of the total area. The area in drought of a drought event j at time t is defined as the sum of unit areas (grid cells) in a drought with: (i) standardized indices SPI, SPEI, SGI, SRI below a threshold (-1.0), or (ii) a flux or state variable below the threshold for one or more grid cells. The sum of total area in drought is divided by the total pan-European area and multiplied by 100 to give the percentage of area in drought in each month up to 7 months ahead. The areal drought duration is defined as the percentiles (10th, 25th, 50th, 75th, and 90th percentiles) of drought duration in all grid cells for each ensemble member. It is similar for areal drought deficit volume.

Technical information

References (1) Peters, E., G. Bier, H.A.J. Van Lanen, and P.J.J.F. Torfs, 2006: Propagation and spatial distribution of drought in a groundwater catchment. J. of Hydrol., 321, 257-275.
References (2) Tallaksen, L.M., H. Hisdal, and H.A.J. Van Lanen, 2009: Space-time modeling of catchment scale drought characteristics. J. of Hydrol., 375, 363-372, doi:10.1016/j.jhydrol.2009.06.032.
References (3) Corzo-Perez, G.A., M.H.J. Van Huijgevoort, F. Voss, and H.A.J. Van Lanen, 2011: On the spatio-temporal analysis of hydrological droughts from global hydrological models. Hydrol. Earth Syst. Sci., 15, 2963-2978, doi:10.5194/hess-15-2963-2011.
References (4) Hisdal, H., and L.M. Tallaksen, 2003: Estimation of regional meteorological and hydrological drought characteristics. J. Hydrol., 281(3), 230 –247.
Developer WUR
Development Stage TRL=5