Comparison of different threshold level methods for drought propagation analysis in Germany

2016 ◽  
Vol 48 (5) ◽  
pp. 1311-1326 ◽  
Author(s):  
B. Heudorfer ◽  
K. Stahl
Keyword(s):  
Threshold Level ◽  
Propagation Characteristics ◽  
Variable Threshold ◽  
Drought Characteristics ◽  
Mountainous Catchments ◽  
Propagation Analysis ◽  
Synoptic Assessment ◽  
Level Method ◽  
A Minor ◽  
Variable Versus

The Threshold Level Method is an approach that enables comparability across all hydrological levels. This advantage is used especially in studies on drought propagation. There are different calculation procedures for this method. The effect that the choice of a variable versus a constant threshold level method has on drought characteristics and drought propagation patterns has not been fully explored yet. Also, most drought propagation studies have analyzed modelled data, suggesting that applicability to observations be tested. We tested the Constant and the Variable Threshold Level Method for the 10th, 20th and 30th percentile on observed precipitation, streamflow, and groundwater data from Germany, and compared drought characteristics and drought propagation patterns by means of statistical analysis and synoptic assessment. The characteristic effects of choosing a variable versus a constant threshold are: (1) a substantial increase in short droughts, (2) a moderate decrease in intermediate droughts and (3) a minor increase in long droughts. Furthermore, in slow-reacting lowland catchments, theoretical propagation characteristics could mostly be confirmed. In faster-reacting upland catchments, this was not always the case and considerable differences arose. Sources of ambiguity were predominantly groundwater in lowlands and streamflow in the mountainous catchments. In conclusion, there is potential of diverging inference from the same data, depending on the chosen methodology.

scholarly journals A generic method for hydrological drought identification across different climate regions

2012 ◽  
Vol 16 (8) ◽  
pp. 2437-2451 ◽  
Author(s):  
M. H. J. van Huijgevoort ◽  
P. Hazenberg ◽  
H. A. J. van Lanen ◽  
R. Uijlenhoet
Keyword(s):  
Land Surface ◽  
Threshold Level ◽  
Global Scale ◽  
Hydrological Drought ◽  
Dry Period ◽  
Drought Duration ◽  
Variable Threshold ◽  
The World ◽  
Level Method ◽  
Zero Runoff

Abstract. The identification of hydrological drought at global scale has received considerable attention during the last decade. However, climate-induced variation in runoff across the world makes such analyses rather complicated. This especially holds for the drier regions of the world (both cold and warm), where, for a considerable period of time, zero runoff can be observed. In the current paper, we present a method that enables to identify drought at global scale across climate regimes in a consistent manner. The method combines the characteristics of the classical variable threshold level method that is best applicable in regions with non-zero runoff most of the time, and the consecutive dry days (period) method that is better suited for areas where zero runoff occurs. The newly presented method allows a drought in periods with runoff to continue in the following period without runoff. The method is demonstrated by identifying droughts from discharge observations of four rivers situated within different climate regimes, as well as from simulated runoff data at global scale obtained from an ensemble of five different land surface models. The identified drought events obtained by the new approach are compared to those resulting from application of the variable threshold level method or the consecutive dry period method separately. Results show that, in general, for drier regions, the threshold level method overestimates drought duration, because zero runoff periods are included in a drought, according to the definition used within this method. The consecutive dry period method underestimates drought occurrence, since it cannot identify droughts for periods with runoff. The developed method especially shows its relevance in transitional areas, because, in wetter regions, results are identical to the classical threshold level method. By combining both methods, the new method is able to identify single drought events that occur during positive and zero runoff periods, leading to a more realistic global drought characterization, especially within drier environments.

scholarly journals The challenges of hydrological drought definition, quantification and communication: an interdisciplinary perspective

2020 ◽  
Vol 383 ◽  
pp. 291-295
Author(s):  
Kerstin Stahl ◽  
Jean-Philippe Vidal ◽  
Jamie Hannaford ◽  
Erik Tijdeman ◽  
Gregor Laaha ◽  
...  
Keyword(s):  
Paradigm Shift ◽  
Threshold Level ◽  
Hydrological Drought ◽  
Low Flow ◽  
Drought Indices ◽  
Drought Frequency ◽  
Variable Threshold ◽  
Group Members ◽  
Level Method ◽  
Identification And Characterization

Abstract. Numerous indices exist for the description of hydrological drought. The EURO FRIEND-Water Low flow and Drought Group has repeatedly discussed changing paradigms in the perception and use of existing and emerging new indices for hydrological drought identification and characterization. Group members have also tested the communication of different indices to stakeholders in several national and international transdisciplinary research projects. This contribution presents the experience gained with regard to the purpose and applicability of different classes of drought indices. A recent paradigm shift is the use of anomalies, traditionally from climatology, in hydrology. For instance, anomaly-based indices, such as the Standardized Streamflow Index (SSI) and the variable threshold level method to define streamflow deficiencies, are used increasingly for real-time monitoring. How these indices relate to low flows and their impacts may have become less clear as a result. Assessments of the severity of a particular drought may also differ depending on whether return periods based on traditional low flow or drought frequency analyses or whether SSI time series index values are used. These experiences call for a systematic comparison, classification and evaluation of different low flow and drought indices and their usages.

scholarly journals A generic method for hydrological drought identification across different climate regions

2012 ◽  
Vol 9 (2) ◽  
pp. 2033-2070 ◽  
Author(s):  
M. H. J. van Huijgevoort ◽  
P. Hazenberg ◽  
H. A. J. van Lanen ◽  
R. Uijlenhoet
Keyword(s):  
Land Surface ◽  
Threshold Level ◽  
Global Scale ◽  
Hydrological Drought ◽  
Dry Period ◽  
Drought Duration ◽  
Variable Threshold ◽  
The World ◽  
Level Method ◽  
Zero Runoff

Abstract. The identification of hydrological drought at global scale has received considerable attention during the last decade. However, climate-induced variation in runoff across the world makes such analyses rather complicated. This especially holds for the drier regions of the world (both cold and warm), where for a considerable period of time, zero runoff can be observed. In the current paper, we present a method that enables to identify drought at global scale across climate regimes in a consistent manner. The method combines the characteristics of the classical variable threshold level method that is best applicable in regions with non zero runoff most of the time, and the consecutive dry days (period) method that is better suited for areas where zero runoff occurs. The newly presented method allows a drought in periods with runoff to continue in the following period without runoff. The method was demonstrated by identifying droughts from discharge observations of four rivers situated within different climate regimes, as well as from simulated runoff data at global scale obtained from an ensemble of five different land surface models. The identified drought events obtained by the new approach were compared to those resulting from application of the variable threshold level method or the consecutive dry period method separately. Results show that, in general, for drier regions, the threshold level method overestimates drought duration, because zero runoff periods were included in a drought, according to the definition used within this method. The consecutive dry period method underestimates drought occurrence, since it cannot identify droughts for periods with runoff. The developed method especially shows its relevance in transitional areas, because in wetter regions, results were identical to the classical threshold level method. By combining both methods, the new method is able to identify single drought events that occur during positive and zero runoff periods, leading to a more realistic global drought characterization, especially within drier environments.

scholarly journals Development of streamflow drought severity–duration–frequency curves using the threshold level method

2014 ◽  
Vol 18 (9) ◽  
pp. 3341-3351 ◽  
Author(s):  
J. H. Sung ◽  
E.-S. Chung
Keyword(s):  
Water Deficit ◽  
Central Government ◽  
Threshold Level ◽  
Drought Severity ◽  
Total Water ◽  
Drought Duration ◽  
Variable Threshold ◽  
Daily Streamflow ◽  
Level Method ◽  
Yield Threshold

Abstract. This study developed a streamflow drought severity–duration–frequency (SDF) curve that is analogous to the well-known depth–duration–frequency (DDF) curve used for rainfall. Severity was defined as the total water deficit volume to target threshold for a given drought duration. Furthermore, this study compared the SDF curves of four threshold level methods: fixed, monthly, daily, and desired yield for water use. The fixed threshold level in this study is the 70th percentile value (Q70) of the flow duration curve (FDC), which is compiled using all available daily streamflows. The monthly threshold level is the monthly varying Q70 values of the monthly FDC. The daily variable threshold is Q70 of the FDC that was obtained from the antecedent 365 daily streamflows. The desired-yield threshold that was determined by the central government consists of domestic, industrial, and agricultural water uses and environmental in-stream flow. As a result, the durations and severities from the desired-yield threshold level were completely different from those for the fixed, monthly and daily levels. In other words, the desired-yield threshold can identify streamflow droughts using the total water deficit to the hydrological and socioeconomic targets, whereas the fixed, monthly, and daily streamflow thresholds derive the deficiencies or anomalies from the average of the historical streamflow. Based on individual frequency analyses, the SDF curves for four thresholds were developed to quantify the relation among the severities, durations, and frequencies. The SDF curves from the fixed, daily, and monthly thresholds have comparatively short durations because the annual maximum durations vary from 30 to 96 days, whereas those from the desired-yield threshold have much longer durations of up to 270 days. For the additional analysis, the return-period–duration curve was also derived to quantify the extent of the drought duration. These curves can be an effective tool to identify streamflow droughts using severities, durations, and frequencies.

scholarly journals Development of streamflow drought severity- and magnitude-duration-frequency curves using the threshold level method

2013 ◽  
Vol 10 (12) ◽  
pp. 14675-14704 ◽  
Author(s):  
J. H. Sung ◽  
E.-S. Chung ◽  
K. S. Lee
Keyword(s):  
Water Deficit ◽  
Threshold Level ◽  
Drought Severity ◽  
Drought Duration ◽  
Water Resources Systems ◽  
Variable Threshold ◽  
Threshold Levels ◽  
Level Method ◽  
Intensity Duration Frequency ◽  
Curve Severity

Abstract. This study developed a comprehensive method to quantify streamflow drought severity and magnitude based on a traditional frequency analysis. Two types of curve were developed: the streamflow drought severity-duration-frequency (SDF) curve and the streamflow drought magnitude-duration-frequency (MDF) curve (e.g., a rainfall intensity-duration-frequency curve). Severity was represented as the total water deficit volume for the specific drought duration, and magnitude was defined as the daily average water deficit. The variable threshold level method was introduced to set the target instream flow requirement, which can significantly affect the streamflow drought severity and magnitude. The four threshold levels utilized were fixed, monthly, daily, and desired yield for water use. The threshold levels for the desired yield differed considerably from the other levels and represented more realistic conditions because real water demands were considered. The streamflow drought severities and magnitudes from the four threshold methods could be derived at any frequency and duration from the generated SDF and MDF curves. These SDF and MDF curves are useful in designing water resources systems for streamflow drought and water supply management.

scholarly journals From meteorological to hydrological drought using standardised indicators

2016 ◽  
Vol 20 (6) ◽  
pp. 2483-2505 ◽  
Author(s):  
Lucy J. Barker ◽  
Jamie Hannaford ◽  
Andrew Chiverton ◽  
Cecilia Svensson
Keyword(s):  
Time Series ◽  
Hydrological Drought ◽  
Annual Rainfall ◽  
Strongly Correlated ◽  
Propagation Characteristics ◽  
The South ◽  
Drought Characteristics ◽  
The North ◽  
The Uk ◽  
Hydrological Droughts

Abstract. Drought monitoring and early warning (M & EW) systems are a crucial component of drought preparedness. M & EW systems typically make use of drought indicators such as the Standardised Precipitation Index (SPI), but such indicators are not widely used in the UK. More generally, such tools have not been well developed for hydrological (i.e. streamflow) drought. To fill these research gaps, this paper characterises meteorological and hydrological droughts, and the propagation from one to the other, using the SPI and the related Standardised Streamflow Index (SSI), with the objective of improving understanding of the drought hazard in the UK. SPI and SSI time series were calculated for 121 near-natural catchments in the UK for accumulation periods of 1–24 months. From these time series, drought events were identified and for each event, the duration and severity were calculated. The relationship between meteorological and hydrological drought was examined by cross-correlating the 1-month SSI with various SPI accumulation periods. Finally, the influence of climate and catchment properties on the hydrological drought characteristics and propagation was investigated. Results showed that at short accumulation periods meteorological drought characteristics showed little spatial variability, whilst hydrological drought characteristics showed fewer but longer and more severe droughts in the south and east than in the north and west of the UK. Propagation characteristics showed a similar spatial pattern with catchments underlain by productive aquifers, mostly in the south and east, having longer SPI accumulation periods strongly correlated with the 1-month SSI. For catchments in the north and west of the UK, which typically have little catchment storage, standard-period average annual rainfall was strongly correlated with hydrological drought and propagation characteristics. However, in the south and east, catchment properties describing storage (such as base flow index, the percentage of highly productive fractured rock and typical soil wetness) were more influential on hydrological drought characteristics. This knowledge forms a basis for more informed application of standardised indicators in the UK in the future, which could aid in the development of improved M & EW systems. Given the lack of studies applying standardised indicators to hydrological droughts, and the diversity of catchment types encompassed here, the findings could prove valuable for enhancing the hydrological aspects of drought M & EW systems in both the UK and elsewhere.

scholarly journals Origin of the galaxy H i size–mass relation

2019 ◽  
Vol 490 (1) ◽  
pp. 96-113 ◽  
Author(s):  
Adam R H Stevens ◽  
Benedikt Diemer ◽  
Claudia del P Lagos ◽  
Dylan Nelson ◽  
Danail Obreschkow ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Surface Density ◽  
Mass Relation ◽  
Local Pressure ◽  
Density Profiles ◽  
Hydrodynamic Simulation ◽  
Variable Threshold ◽  
The Galaxy ◽  
Analytical Argument ◽  
A Minor

ABSTRACT We analytically derive the observed size–mass relation of galaxies’ atomic hydrogen (H i), including limits on its scatter, based on simple assumptions about the structure of H i discs. We trial three generic profiles for H i surface density as a function of radius. First, we assert that H i surface densities saturate at a variable threshold, and otherwise fall off exponentially with radius or, secondly, radius squared. Our third model assumes the total gas surface density is exponential, with the H i fraction at each radius depending on local pressure. These are tested against a compilation of 110 galaxies from the THINGS, LITTLE THINGS, LVHIS, and Bluedisk surveys, whose H i surface density profiles are well resolved. All models fit the observations well and predict consistent size–mass relations. Using an analytical argument, we explain why processes that cause gas disc truncation – such as ram-pressure stripping – scarcely affect the H i size–mass relation. This is tested with the IllustrisTNG(100) cosmological, hydrodynamic simulation and the Dark Sage semi-analytic model of galaxy formation, both of which capture radially resolved disc structure. For galaxies with $m_* \ge 10^9\, {\rm M}_{\odot }$ and $m_{\rm H\, {\small {I}}} \ge 10^8\, {\rm M}_{\odot }$, both simulations predict H i size–mass relations that align with observations, show no difference between central and satellite galaxies, and show only a minor, second-order dependence on host halo mass for satellites. Ultimately, the universally tight H i size–mass relation is mathematically inevitable and robust. Only by completely disrupting the structure of H i discs, e.g. through overly powerful feedback, could a simulation predict the relation poorly.

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