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 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 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.

Global Overview of Tropical Dry Forests

2020 ◽  
pp. 1-23
Author(s):  
G. N. Tanjina Hasnat ◽  
Mohammed Kamal Hossain
Keyword(s):  
Climate Change ◽  
Endangered Species ◽  
Land Surface ◽  
Forest Type ◽  
Conservation Status ◽  
Tropical Dry Forests ◽  
Land Conversion ◽  
Dry Period ◽  
Dry Forests ◽  
The World

Forests cover almost one-third of the Earth's land surface. Tropical dry forests are the second-most-important forest type in the world covering approximately 42% of tropical and sub-tropical forest area. The main features of these forests are their deciduousness, a prolonged dry period extending 3-9 months, and little annual precipitation of 250-2,000 mm. Tropical dry forests are found in five of the eight realms in the world. More than half of the forests are distributed in the Americas, with other portions in Africa, Eurasia, Australia, and Southeast Asia. The forests are unique in nature, and provide shelter to a huge number of endemics and endangered species. Among woody plant species, about 40% are not found anywhere in the world. These forests are now the most threatened among all forest types. The conservation status of these forests is endangered. Deforestation, rapid civilization, land conversion, fire, and climate change are the major threats. Proper management with time-oriented policy could be helpful to restore these forests and protect the existing remnant areas.

scholarly journals Future discharge drought across climate regions around the world modelled with a synthetic hydrological modelling approach forced by three General Circulation Models

2013 ◽  
Vol 1 (6) ◽  
pp. 7701-7738 ◽  
Author(s):  
N. Wanders ◽  
H. A. J. van Lanen
Keyword(s):  
General Circulation ◽  
Reference Model ◽  
Control Period ◽  
General Circulation Models ◽  
Hydrological Drought ◽  
Severe Drought ◽  
Drought Duration ◽  
Increased Risk ◽  
The World ◽  
Drought Occurrence

Abstract. Hydrological droughts characteristics (drought in groundwater and streamflow) likely will change in the 21st century as a results of climate change. Magnitude and directionality of these changes and their dependency on climatology and catchment characteristics, however, is largely unknown. In this study a conceptual hydrological model was forced by downscaled and bias-corrected outcome from three General Circulation Models for the A2 emission scenario (GCM forced models), and the WATCH Forcing Data re-analysis dataset(reference model). The threshold level method was applied to investigate drought occurrence, duration and deficit volume. Results for the control period (1971–2000) show that the drought characteristics of each GCM forced model reasonably agree with the reference model for most of the climate types, suggesting that the climate model's results after post-processing produce realistic outcome for global drought analyses. For the near future (2021–2050) and far future (2071–2100) the GCM forced models show a decrease in drought occurrence for all major climates around the world and increase of both average drought duration and deficit volume of the remaining drought events. The largest decrease in hydrological drought occurrence is expected in cold (D-)climates where global warming results in a decreased length of the snow season and an increased precipitation. In the dry B-climates the smallest decrease in drought occurrence is expected to occur, which probably will lead to even more severe water scarcity. However, in the extreme climate regions (desert and polar), the analysis for the control period showed that projections are in these regions most uncertain. On a global scale the increase in hydrological drought duration and severity will lead to a higher impact of drought events, which urges water resources managers to timely anticipate on the increased risk on more severe drought in groundwater and streamflow and to design pro-active measures.

Analyzing the propagation of drought through water storages using global scale GRACE-based data assimilation

2021 ◽  
Author(s):  
Helena Gerdener ◽  
Kerstin Schulze ◽  
Olga Engels ◽  
Jürgen Kusche ◽  
Hannes Müller Schmied ◽  
...  
Keyword(s):  
Surface Water ◽  
Spatial Resolution ◽  
Land Surface ◽  
Hydrological Model ◽  
Crop Yields ◽  
Global Scale ◽  
Hydrological Drought ◽  
Time Lags ◽  
Satellite Mission

<p>The frequency and severity of drought increase in many regions of the world, which emphasizes the need for sufficient research to better monitor and trigger management plans. An important role hereby plays hydrological drought, because it affects water supply and crop yields that are necessary to ensure food security. Typically, hydrological drought detection is based on in-situ observations of fluxes or storages at the surface. However, this neglects the fact that drought might occur in multiple storages with different timing and severity.  The use of subsurface storage, e.g. groundwater, is rare because the available in-situ well level monitoring is irregularly distributed in space and time and access might be restricted, for example due to national security reasons or problems in converting them to storage estimates.</p><p>The satellite mission Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE-FO offer a great possibility to observe the total water storage, i.e. the sum of surface and subsurface storages, on a global scale from space. However, GRACE is restricted to monthly data on a spatial resolution of about 300 km and the vertical sum of the storages. Hydrological models present another possibility to derive global storage information with a finer spatial (~50km), temporal and vertical resolution than GRACE but they do not perfectly represent the reality because they are underlying assumptions and are affected by uncertainty of forcing data. Therefore, to enable downscaling of GRACE while improving the models realism, the GRACE measurements are assimilated into a hydrological model.</p><p>In previous works we used a framework that assimilates GRACE into the WaterGAP Global Hydrological Model (WGHM) regionally or basin-wise. In this work we present a new framework that globally assimilates GRACE on a 4 degree grid with full uncertainty information from 2003 to 2018. The framework enables to assimilate about 95% of the global WGHM land surface except Greenland. With regard to vertical and spatial resolution the performance of model, observation and assimilation is compared. Global GRACE based drought indicators are applied and its development in the different compartments of surface water, soil and groundwater is analyzed to identify new insights into the propagation of drought. We expect that by including GRACE we derive new information especially for groundwater droughts, which might reveal time lags and a different severity as compared to surface water droughts for some regions.</p>

scholarly journals Hydrological drought across the world: impact of climate and physical catchment structure

2013 ◽  
Vol 17 (5) ◽  
pp. 1715-1732 ◽  
Author(s):  
H. A. J. Van Lanen ◽  
N. Wanders ◽  
L. M. Tallaksen ◽  
A. F. Van Loon
Keyword(s):  
Large Scale ◽  
Hydrological Drought ◽  
Temperate Climate ◽  
Minor Effect ◽  
Hydrological Models ◽  
Drought Duration ◽  
Groundwater System ◽  
Drought Characteristics ◽  
The World ◽  
Groundwater Systems

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.

GRACE a witness to the Recovery of the Tigris-Euphrates Hydrologic System

2020 ◽  
Author(s):  
Mohamed Sultan ◽  
Karem Abdelmohsen ◽  
Himanshu Save
Keyword(s):  
Surface Water ◽  
Land Surface ◽  
Global Precipitation Climatology Project ◽  
Water Levels ◽  
Dry Period ◽  
The Past ◽  
Grace Data ◽  
Precipitation Record ◽  
The World ◽  
Precipitation Events

<p>Global warming is producing climatic changes across the world that affect in major ways the livelihood of major sectors of the world’s population. Over the past decade or two, an increase in the frequency and intensity of specific climatic phenomena (e.g., hurricanes, wet or dry periods, etc.) has been reported from many parts of the globe and is believed to be climate change-related. Over the past few years, the largest and most intense precipitation events were recorded over the Tigris and Euphrates watershed (TEW), a heavily engineered watershed (> 60 main dams) that is shared by Turkey, Iran, Syria, Saudi Arabia, and Iraq. Analysis of the Global Precipitation Climatology Project (GPCP) precipitation record over the past 40 year (1979-present) across the TEW revealed a prolonged dry period (2002- to 2017; Average Annual Precipitation [AAP]: 240 km<sup>3</sup>), followed by wet years (2018 to 2020; AAP: 425 km<sup>3</sup>). The recent extensive precipitation events during the wet period are reflected in GRACE and GRACE-FO data. Throughout the dry period there was a total decline in GRACE<sub>TWS</sub> of 212 km<sup>3</sup> (13.3 km<sup>3</sup>/yr) followed by an increase of 246 km<sup>3</sup> (82 km<sup>3</sup>/yr) during the wet period.  In other words, in the past 2.5 years, the TEW more than recovered its losses during the previous 15 years. This recovery was enabled in part by the impoundment of surface water behind the many dams in the riparian countries and by infiltration of precipitation that recharged the TEW aquifers. Using radar altimetry we observe an increase in surface water levels by 8 m in Lake Ataturk, 13 m in Lake Karakaya, 1.5 m in Lake Van in Turkey, 5 m in Lake Assad in Syria, and 16 m in Lake Tharthar, and 24 m in Lake Mosul in Iraq.  These translate to a volume increase of 21.7 km<sup>3</sup> in Turkey, 3.5 km<sup>3</sup> in Syria, and 34 km<sup>3</sup> in Iraq during the wet period. Using GRACE data and outputs of land surface models, we estimate that groundwater storage GRACE<sub>TWS</sub> declined at a rate of -7 km<sup>3</sup>/yr during the dry period and increased at a rate of 60 km<sup>3</sup>/yr during the wet years.</p>

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