Using SIMGRO for drought analysis – as demonstrated for the Taquari Basin, Brazil

Tools were developed and tested to quantify space–time development of droughts at the river basin scale. The spatial development of a hydrological drought in river basins brings different challenges to describe drought characteristics, such as: area in a drought and areal expressions for onset, duration and severity. We used the regional hydrological model SIMGRO in a GIS framework to generate the spatially-distributed time series for the drought analysis. Droughts in different hydrological variables (recharge and groundwater discharge) were identified by applying the fixed threshold concept to the time series. The method captures the development of both the duration and the severity of the area in a drought. The GIS helps to better understand the link between areal drought characteristics and spatially-distributed catchment characteristics. Functions, like agriculture, nature or navigation in a region, need to be considered more in defining the appropriate threshold levels. It is also important to take into account varying hydrological conditions like regions with deep or shallow groundwater levels, resulting in periods with capillary rise in the unsaturated zone in the latte

Drought and Water Scarcity in Europe: past and future (Secheresse et déficit d’eau en Europe: passé et perspective)

Low river flows and droughts are increasingly being observed over the last decades in Europe. Moreover, in vast areas drought will likely increase due to climate change? The increasing trends to more severe drought are explained in the context of growing water scarcity that also is reported in many European regions. Water scarcity often enhances drought impacts. First, trends in historic European drought events are discussed. Then understanding of transformation of meteorological drought into soil moisture and hydrological drought (groundwater, streamflow), which is called drought propagation, is described. Knowledge on drought propagation is essential for water resources management. Water scarcity in Europe and its spatial distribution is touched upon, incl. an observational-modelling framework that is being proposed to distinguish between water scarcity and drought. We conclude with an assessment of future drought and water scarcity due to global change and implication of the use of modeling chain approaches, incl. uncertainty

On the spatio-temporal analysis of hydrological droughts from global hydrological models

The recent concerns for world-wide extreme events related to climate change have motivated the development of large scale models that simulate the global water cycle. In this context, analysis of hydrological extremes is important and requires the adaptation of identification methods used for river basin models. This paper presents two methodologies that extend the tools to analyze spatio-temporal drought development and characteristics using large scale gridded time series of hydrometeorological data. The methodologies are classified as non-contiguous and contiguous drought area analyses (i.e. NCDA and CDA). The NCDA presents time series of percentages of areas in drought at the global scale and for pre-defined regions of known hydroclimatology. The CDA is introduced as a complementary method that generates information on the spatial coherence of drought events at the global scale. Spatial drought events are found through CDA by clustering patterns (contiguous areas). In this study the global hydrological model WaterGAP was used to illustrate the methodology development. Global gridded time series of subsurface runoff (resolution 0.5°) simulated with the WaterGAP model from land points were used. The NCDA and CDA were developed to identify drought events in runoff. The percentages of area in drought calculated with both methods show complementary information on the spatial and temporal events for the last decades of the 20th century. The NCDA provides relevant information on the average number of droughts, duration and severity (deficit volume) for pre-defined regions (globe, 2 selected hydroclimatic regions). Additionally, the CDA provides information on the number of spatially linked areas in drought, maximum spatial event and their geographic location on the globe. Some results capture the overall spatio-temporal drought extremes over the last decades of the 20th century. Events like the El Niño Southern Oscillation (ENSO) in South America and the pan-European drought in 1976 appeared clearly in both analyses. The methodologies introduced provide an important basis for the global characterization of droughts, model inter-comparison of drought identified from global hydrological models and spatial event analyse

Qualitative and quantitative physical land evaluation : an operational approach

Physical land evaluation methods are crucial for evaluating potentials and constraints of land for intended land use. Physical resources, such as soil, climate, hydrology, and topography are evaluated. Different technical procedures are used for physical land evaluation ranging from simple methods based on expert knowledge to more complex methods based on simulation models. The expert knowledge is derived from farmers' experiences. The methods using expert knowledge provide broad descriptive answers regarding land qualities and suitability and, therefore, they are described as qualitative evaluation methods. Qualitative physical land evaluation methods are developed and applied to screen possibilities of Dutch land for injection of slurry from animal manure, and to assess the growth potential of sugar-beet in the European Communities. Quick answers are obtained if the knowledge is captured into expert models in a computer system and when they are linked to a geographical information system.The more complex methods are based on computer models simulating transient soilwater flow and crop growth. These methods are described as quantitative because they produce specific expressions in quantitative terms, such as occurrence probabilities of soilwater deficits, average crop yields, and temporal variabilities of crop yields. Quantitative methods are elaborated and their abilities are illustrated with the assessment of growth potential of potatoes in the Netherlands, and of sugar-beet and wheat in the European Communities. The impact of some land use options on crop production is explored, such as set-aside of land. Quantitative evaluation yields more specific results than qualitative evaluation, but it is more time-consuming and requires more specific input data. Because of these higher demands, a mixed qualitative/quantitative evaluation approach is introduced. In this approach expert models are used to screen land for severe restrictions for a defined use, and, subsequently, simulation models are applied to the remaining potentially suited land. An analysis of required efforts for various evaluation approaches is presented.Finally, a quantitative physical land evaluation is elaborated to assess the effects of soil management on soil structure degradation and regeneration on farm scale. The major role of the land characteristic "soil macrostructure" is described. Several soil-structure types resulting from different soil management systems are recognized in sandy loam and clay loam soils, and characterized quantitatively in soil-morphological and soil-physical terms. The data are used as input for a soil- water flow model to calculate water-associated land qualities for land units with different soil- structure types. Differences in land qualities are interpreted as effects of soil-structure change. The modifications of the soil-water flow model to account for bypass flow and internal catchment (subsurface infiltration) are described