Abstract
Abstract. Large-scale hydrological drought studies have demonstrated spatial and temporal patterns in observed trends, and considerable difference exists among global hydrological models in their ability to reproduce these patterns. In this study a controlled modeling experiment has been set up to systematically explore the role of climate and physical catchment structure (soils and groundwater systems) to better understand underlying drought-generating mechanisms. Daily climate data (1958–2001) of 1495 grid cells across the world were selected that represent Köppen–Geiger major climate types. These data were fed into a conceptual hydrological model. Nine realizations of physical catchment structure were defined for each grid cell, i.e., three soils with different soil moisture supply capacity and three groundwater systems (quickly, intermediately and slowly responding). Hydrological drought characteristics (number, duration and standardized deficit volume) were identified from time series of daily discharge. Summary statistics showed that the equatorial and temperate climate types (A- and C-climates) had about twice as many drought events as the arid and polar types (B- and E-climates), and the durations of more extreme droughts were about half the length. Selected soils under permanent grassland were found to have a minor effect on hydrological drought characteristics, whereas groundwater systems had major impact. Groundwater systems strongly controlled the hydrological drought characteristics of all climate types, but particularly those of the wetter A-, C- and D-climates because of higher recharge. The median number of droughts for quickly responding groundwater systems was about three times higher than for slowly responding systems. Groundwater systems substantially affected the duration, particularly of the more extreme drought events. Bivariate probability distributions of drought duration and standardized deficit for combinations of Köppen–Geiger climate, soil and groundwater system showed that the responsiveness of the groundwater system is as important as climate for hydrological drought development. This urges for an improvement of subsurface modules in global hydrological models to be more useful for water resources assessments. A foreseen higher spatial resolution in large-scale models would enable a better hydrogeological parameterization and thus inclusion of lateral flow.
Highlights
Drought, desertification and other forms of water shortage are anticipated to affect as many as one-third of the world’s population
Drought duration and standardized deficit volume (DDSDV) for each drought event were derived from the simulated time series of discharge for each of the selected grid cells (Table 1)
First this was done for grid cells with a soil of medium soil moisture supply capacity (Soil II) and an intermediately responding groundwater system (j = 250 day), hereafter called the reference situation
Summary
Desertification and other forms of water shortage are anticipated to affect as many as one-third of the world’s population. Over 0.5 billion people in regions in China and India are annually exposed to droughts that seriously affect economic development and environment. In western African countries, where on average over 30 % of the people are exposed to drought every year, the livelihood of the people is seriously threatened (e.g., ISDR, 2009; WWDR, 2009). In 2011, a severe drought affected the entire East Africa region and contributed to a severe food crisis across Djibouti, Ethiopia, Kenya and Somalia. It threatened the livelihood of more than
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