Hydrological Drought Assessment Based on the Standardized Streamflow Index: A Case Study of the Three Cape Provinces of South Africa

Global impacts of drought conditions pose a major challenge towards the achievement of the 2030 Sustainable Development Goals. As a result, a clarion call for nations to take actions aimed at mitigating the adverse negative effects, managing key natural resources and strengthening socioeconomic development can never be overemphasized. The present study evaluated hydrological drought conditions in three Cape provinces (Eastern, Western and Northern Cape) of South Africa, based on the Standardized Streamflow Index (SSI) calculated at 3- and 6-month accumulation periods from streamflow data spanning over the 3.5 decades. The SSI features were quantified by assessing the corresponding annual trends computed by using the Modified Mann–Kendall test. Drought conditions were also characterized in terms of the duration and severity across the three Cape provinces. The return levels of drought duration (DD) and drought severity (DS) associated with 2-, 5-, 10-, 20- and 50-year periods were estimated based on the generalized extreme value (GEV) distribution. The results indicate that hydrological drought conditions have become more frequent and yet exhibit spatial contrasts throughout the study region during the analyzed period. To this end, there is compelling evidence that DD and DS have increased over time in the three Cape provinces. Return levels analysis across the studied periods also indicate that DD and DS are expected to be predominant across the three Cape provinces, becoming more prolonged and severe during the extended periods (e.g., 20- and 50-year). The results of the present study (a) contribute to the scientific discourse of drought monitoring, forecasting and prediction and (b) provide practical insights on the nature of drought occurrences in the region. Consequently, the study provides the basis for policy- and decision-making in support of preparedness for and adaptation to the drought risks in the water-linked sectors and robust water resource management. Based on the results reported in this study, it is recommended that water agencies and the government should be more proactive in searching for better strategies to improve water resources management and drought mitigation in the region.

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Uncertainties in runoff projection and hydrological drought assessment over Gharesu basin under CMIP5 RCP scenarios

Journal of Water and Climate Change ◽

10.2166/wcc.2020.088 ◽

2020 ◽

Vol 11 (S1) ◽

pp. 145-163 ◽

Cited By ~ 1

Author(s):

S. M. Ashrafi ◽

H. Gholami ◽

M. R. Najafi

Keyword(s):

River Basin ◽

General Circulation ◽

General Circulation Models ◽

Hydrological Drought ◽

Drought Severity ◽

Historical Period ◽

Drought Duration ◽

Rcp Scenarios ◽

Drought Assessment ◽

Drought Characteristics

Abstract Hydrological drought plays an important role in planning and managing water resources systems to meet increasing water demands due to population growth. In this study, the effects of climate change on the hydrological drought characteristics of the Gharasu basin, as one of the major sub-basins of the Karkheh river basin, are investigated. This river basin has experienced severe droughts, and floods, in recent years. The uncertainties in projected drought conditions are characterized based on a suite of 34 general circulation models (GCMs). Based on hydrological simulations over the historical period, 12 GCMs are selected to estimate projected runoff values and the corresponding streamflow drought index (SDI) in the future period. The ‘run theory’ is applied to evaluate the drought characteristics under Representative Concentration Pathways (RCPs) 4.5 and 8.5 emission scenarios. Results show that uncertainties of drought projection under RCP8.5 are higher than under RCP4.5, where among different drought characteristics, the maximum uncertainty is detected for drought severity and maximum drought duration. Moreover, the uncertainty of drought projection in wet periods is greater than that in dry periods.

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Assessment of the Dissimilarities of EDI and SPI Measures for Drought Determination in South Africa

Water ◽

10.3390/w13010082 ◽

2021 ◽

Vol 13 (1) ◽

pp. 82

Author(s):

Omolola M. Adisa ◽

Muthoni Masinde ◽

Joel O. Botai

Keyword(s):

South Africa ◽

South African ◽

Correlation Coefficient ◽

Pearson Correlation ◽

Standardized Precipitation Index ◽

Drought Monitoring ◽

Drought Indices ◽

Drought Severity ◽

Pearson Correlation Coefficient ◽

Drought Duration

This study examines the (dis)similarity of two commonly used indices Standardized Precipitation Index (SPI) computed over accumulation periods 1-month, 3-month, 6-month, and 12-month (hereafter SPI-1, SPI-3, SPI-6, and SPI-12, respectively) and Effective Drought Index (EDI). The analysis is based on two drought monitoring indicators (derived from SPI and EDI), namely, the Drought Duration (DD) and Drought Severity (DS) across the 93 South African Weather Service’s delineated rainfall districts over South Africa from 1980 to 2019. In the study, the Pearson correlation coefficient dissimilarity and periodogram dissimilarity estimates were used. The results indicate a positive correlation for the Pearson correlation coefficient dissimilarity and a positive value for periodogram of dissimilarity in both the DD and DS. With the Pearson correlation coefficient dissimilarity, the study demonstrates that the values of the SPI-1/EDI pair and the SPI-3/EDI pair exhibit the highest similar values for DD, while the SPI-6/EDI pair shows the highest similar values for DS. Moreover, dissimilarities are more obvious in SPI-12/EDI pair for DD and DS. When a periodogram of dissimilarity is used, the values of the SPI-1/EDI pair and SPI-6/EDI pair exhibit the highest similar values for DD, while SPI-1/EDI displayed the highest similar values for DS. Overall, the two measures show that the highest similarity is obtained in the SPI-1/EDI pair for DS. The results obtainable in this study contribute towards an in-depth knowledge of deviation between the EDI and SPI values for South Africa, depicting that these two drought indices values are replaceable in some rainfall districts of South Africa for drought monitoring and prediction, and this is a step towards the selection of the appropriate drought indices.

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Hydrological Drought Regimes of the Huai River Basin, China: Probabilistic Behavior, Causes and Implications

Water ◽

10.3390/w11112390 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2390 ◽

Cited By ~ 1

Author(s):

Sun ◽

Zhang ◽

Yao ◽

Wen

Keyword(s):

River Basin ◽

Hydrological Drought ◽

Drought Severity ◽

Copula Functions ◽

Drought Duration ◽

Huai River Basin ◽

Huai River ◽

The Impact ◽

Hydrological Droughts ◽

The Huai River Basin

: Hydrological droughts were characterized using the run-length theory and the AIC (Akaike information criterion) techniques were accepted to evaluate the modeling performance of nine probability functions. In addition, the copula functions were used to describe joint probability behaviors of drought duration and drought severity for the major tributaries of the Huai River Basin (HRB) which is located in the transitional zone between humid and semi-humid climates. The results indicated that: (1) the frequency of hydrological droughts in the upper HRB is higher than that in the central HRB, while the duration of the hydrological drought is in reverse spatial pattern. The drought frequency across the Shiguan River along the south bank of the HRB is higher than the other two tributaries; (2) generalized Pareto distribution is the appropriate distribution function with the best performance in modelling the drought duration over the HRB; while the Generalized Extreme Value (GEV) distribution can effectively describe the probabilistic properties of the drought severity. Joe copula and Tawn copula functions are the best choices and were used in this study. Given return periods of droughts of <30 years, the droughts in the upper HRB are the longest, and the shortest are in the central HRB; (3) the frequency of droughts along the mainstream of the HRB is higher than tributaries of the HRB. However, concurrence probability of droughts along the mainstream of the HRB is lower than the tributaries of the HRB. The drought resistance capacity of HRB has been significantly improved, effectively reducing the impact of hydrological drought on crops after 2010.

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Research Trends of Hydrological Drought: A Systematic Review

Water ◽

10.3390/w11112252 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2252 ◽

Cited By ~ 3

Author(s):

Hasrul Hazman Hasan ◽

Siti Fatin Mohd Razali ◽

Nur Shazwani Muhammad ◽

Asmadi Ahmad

Keyword(s):

Systematic Review ◽

Scientific Evidence ◽

Flow Analysis ◽

Hydrological Drought ◽

Low Flow ◽

Drought Severity ◽

Spatial And Temporal Variability ◽

Drought Vulnerability ◽

Regional Modelling ◽

Drought Assessment

The frequency and severity of global drought-induced impacts have led to raising awareness of the need for improved river management. Although academic publications on drought have proliferated, a systematic review of literature has not yet been conducted to identify trends, themes, key topics, and authorships. This study aims to evaluate the scientific evidence for the hydrological drought characteristics and the methodologies by performing as a framework. This systematic review performed three-stage screening of literature review for current applicable hydrological drought studies that have been conducted since the year of 2000 concerning methodologies, literature research gaps, and trends, and contribute to future studies. The analysis shows the increasing trends of research and publications in the hydrological drought assessment. The primary research themes are hydrological drought is drought severity, drought vulnerability, and drought forecast. Despite the current research findings, spatial and temporal variability, low flow analysis and regional modelling are the most important to encourage a holistic approach and international collaborations. The finding identified the shortcomings of most research, which are the use of non-standardized methodological and distinct sample sizes, resulting in data summary challenges and unrealistic comparisons.

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Identification of the Space-Time Variability of Hydrological Drought in the Arid Region of Northwestern China

Water ◽

10.3390/w11051051 ◽

2019 ◽

Vol 11 (5) ◽

pp. 1051 ◽

Cited By ~ 1

Author(s):

Huaijun Wang ◽

Zhongsheng Chen ◽

Yaning Chen ◽

Yingping Pan ◽

Ru Feng

Keyword(s):

Arid Region ◽

Water Resource Management ◽

Space Time ◽

Hydrological Drought ◽

Northwestern China ◽

Logistic Distribution ◽

Time Variability ◽

Drought Duration ◽

Monthly Streamflow ◽

Drought Duration And Severity

Drought monitoring is crucial to water resource management and strategic planning. Thus, the objective of this study is to identify the space-time variability of hydrological drought across the broad arid region of northwestern China. Seven distributions were applied to fitting monthly streamflow records of 16 gauging stations from 10 rivers. Finally, the general logistic distribution was selected as the most appropriate one to compute the Standardized Streamflow Index (SSI). The severity and duration of hydrological droughts were also captured from the SSI series. Moreover, we investigate the relationship between hydrological drought (SSI) and meteorological drought (Standardized Precipitation-Evapotranspiration Index (SPEI)) at different time scales. The results show that drought duration and severity decreased over time in the Aibihu, Irtysh, Kaidu, Aksu, Yarkand, Hoton, Shule, Heihe (upstream), and Shiyang Rivers. However, the Tarim (upstream) and Heihe (middle stream) Rivers showed increasing drought duration and severity and this can be attributed to recent decades human activities. Furthermore, two correlation coefficient patterns between SSI and SPEI were found for the rivers of interest, an “increasing-decreasing” pattern for the Irtysh, Heihe, and Shiyang Rivers, where the precipitation is the main runoff supply, and an “increasing-stable” pattern for Aibihu and the Kaidu, Aksu, Yarkand, Hotan, and Shule Rivers, where glacier melt water provided a relatively high supply of runoff. Our findings are a contribution towards implementing effective water resources evaluation and planning in this arid region.

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Short-Term and Medium-Term Drought Forecasting Using Generalized Additive Models

Sustainability ◽

10.3390/su12104006 ◽

2020 ◽

Vol 12 (10) ◽

pp. 4006

Author(s):

Fhumulani Mathivha ◽

Caston Sigauke ◽

Hector Chikoore ◽

John Odiyo

Keyword(s):

South Africa ◽

Time Series ◽

Water Resource Management ◽

Generalized Additive Models ◽

Additive Models ◽

Drought Risk ◽

Drought Forecasting ◽

Medium Term ◽

Drought Conditions ◽

Semi Arid

Forecasting extreme hydrological events is critical for drought risk and efficient water resource management in semi-arid environments that are prone to natural hazards. This study aimed at forecasting drought conditions in a semi-arid region in north-eastern South Africa. The Standardized Precipitation Evaporation Index (SPEI) was used as a drought-quantifying parameter. Data for SPEI formulation for eight weather stations were obtained from South Africa Weather Services. Forecasting of the SPEI was achieved by using Generalized Additive Models (GAMs) at 1, 6, and 12 month timescales. Time series decomposition was done to reduce time series complexities, and variable selection was done using Lasso. Mild drought conditions were found to be more prevalent in the study area compared to other drought categories. Four models were developed to forecast drought in the Luvuvhu River Catchment (i.e., GAM, Ensemble Empirical Mode Decomposition (EEMD)-GAM, EEMD-Autoregressive Integrated Moving Average (ARIMA)-GAM, and Forecast Quantile Regression Averaging (fQRA)). At the first two timescales, fQRA forecasted the test data better than the other models, while GAMs were best at the 12 month timescale. Root Mean Square Error values of 0.0599, 0.2609, and 0.1809 were shown by fQRA and GAM at the 1, 6, and 12 month timescales, respectively. The study findings demonstrated the strength of GAMs in short- and medium-term drought forecasting.

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Conjunctive Operation of Surface and Subsurface Dams Based on Drought Severity

Water ◽

10.3390/w13060847 ◽

2021 ◽

Vol 13 (6) ◽

pp. 847

Author(s):

Bo Ram Kim ◽

Sang-Il Lee

Keyword(s):

Water Supply ◽

Water Demand ◽

Water Allocation ◽

Water Resource Management ◽

Management Tool ◽

Drought Severity ◽

Domestic Water ◽

Water Shortages ◽

Drought Duration ◽

Groundwater Dam

As an effective water management method to respond to the increasing severity of drought, this study proposed a conjunctive operation using a surface reservoir and subsurface dams. The proposed methodology predicts the probable rainfall according to the drought severity and the water demand, and uses these as the basis for water allocation. Sokcho City, located in South Korea, was used as the study case. Sokcho is a tourist city that has suffered from water shortages for many years due to its excessive dependence on a single groundwater dam. Considering conjunctive operation, drought frequency, and drought duration, a total of 80 cases under four scenarios were generated and simulated to determine the water supply capability over the entire year. The results indicate that domestic water can be supplied throughout the year with appropriate water allocation, even when a once-in-50-year drought lasts for 120 days. Furthermore, the water supply potential, which is the additionally available capacity in a reservoir, was used to assess the effects of conjunctive operation. It was estimated that, for a once-in-10-year drought, up to 318% of the annual water demand was available in the reservoir. As the proposed methodology is relatively simple, it offers a useful water resource management tool for sites with similar social and environmental conditions.

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Estimating Return Intervals for Extreme Climate Conditions Related to Winter Disasters and Livestock Mortality in Mongolia

10.5194/nhess-2021-258 ◽

2021 ◽

Author(s):

Masahiko Haraguchi ◽

Nicole Davi ◽

Mukund Rao ◽

Caroline Leland ◽

Masataka Watanabe ◽

...

Keyword(s):

Minimum Temperature ◽

Drought Severity ◽

Summer Drought ◽

Early 19Th Century ◽

Climate Conditions ◽

Winter Conditions ◽

Return Levels ◽

Drought Conditions ◽

Winter Minimum Temperature ◽

Winter Severity

Abstract. Mass livestock mortality events during severe winters, a phenomenon that Mongolians call dzud, cause the country significant socioeconomic problems. Dzud is an example of a compound event, meaning that multiple climatic and social drivers contribute to the risk of occurrence. Existing studies argue that the frequency and intensity of dzud are rising due to the combined effects of climate change and variability, most notably summer drought and severe winter conditions, on top of socioeconomic dynamics such as overgrazing. Summer droughts are a precondition for dzud because scarce grasses cause malnutrition, which in turn makes livestock more vulnerable to harsh winter conditions. However, these studies typically look at a short time frame (i.e., after 1940); few have investigated either the risk or the recurrence of dzud over a century-scale climate record. This study aims to fill the gaps in technical knowledge about the recurrence probability of dzud by estimating the return levels of relevant climatic variables: summer drought conditions and winter minimum temperature. We divide the country into three regions (Northwest, Southwest, and East Mongolia) based on the mortality index at the soum (county) level. For droughts, our study uses as a proxy the tree-ring reconstructed Palmer Drought Severity Index (PDSI) for three regions between 1700–2013. For winter severity, our study uses observational data of winter minimum temperature after 1901 while inferring winter minimum temperature in Mongolia from instrumental data in Siberia that extends to the early 19th century. The Generalized Extreme Value (i.e., the statistical method to infer the probability of very rare or extreme events) shows that the return levels of drought conditions are changing over time, with variability increasing for all the regions. Winter severity, however, is constant. The median 100-year return levels of the winter minimum temperature in Mongolia have been, over the past 300 years, −26.08 °C for the Southwest, −27.99 °C for the Northwest, and −25.31 °C for the East. This study thus suggests that continued summer drought would lead to increased vulnerability and malnutrition. Here, we link meteorological characteristics to socioeconomic impacts related to livestock populations and draws attention to the need for livestock index insurance.

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An Analysis of Precipitation Extreme Events Based on the SPI and EDI Values in the Free State Province, South Africa

Water ◽

10.3390/w13213058 ◽

2021 ◽

Vol 13 (21) ◽

pp. 3058

Author(s):

Omolola M. Adeola ◽

Muthoni Masinde ◽

Joel O. Botai ◽

Abiodun M. Adeola ◽

Christina M. Botai

Keyword(s):

South Africa ◽

Extreme Precipitation ◽

Water Resource Management ◽

Early Warning Systems ◽

Generalized Extreme Value Distribution ◽

Free State ◽

Annual Rainfall ◽

Return Periods ◽

Free State Province ◽

Return Levels

Recognizing that, over the last several years, extreme rainfall has led to hazardous stress in humans, animals, plants, and even infrastructure, in the present study, we aimed to investigate the characteristics of droughts over the Free State (FS) Province of South Africa in order to determine the future likelihood of reoccurrences of precipitation extremes using the generalized extreme value distribution (GEV) and extreme frequency analysis (EFA). In this regard, daily rainfall datasets from nine South African weather service homogenous climatic districts, spanning from 1980 to 2019, were used to compute: (a) the total annual rainfall, (b) the Effective Drought Index (EDI), and (c) the Standard Precipitation Index (SPI). The SPI was calculated for 3, 6, and 12 month accumulation periods (hereafter SPI-3, SPI-6, and SPI-12, respectively). The trend analysis results of the EDI and SPI-3, -6, and -12 showed that the Free State Province is generally negative, illustrating persistent drought. An analysis of the GEV parameters across the EDI and SPI-3, -6, and -12 values illustrated that the location, scale, and shape parameters exhibited a noticeable spatial variability across the Free State Province with the location parameter largely negative, the scale parameter largely positive, while the shape parameter pointed to an inherent Type III (Weibull) GEV distribution. In addition, the return levels for the drought/wet duration and severity of the EDI and SPI-3, -6, and -12 values generally showed increasing patterns across the corresponding return periods; the spatial contrasts were only noticeable in the return levels derived from the wet/drought duration and severity derived from SPI-3, -6, and -12 values (and not in the EDI). Further, the EFA results pointed to a noticeable spatial contrast in the return periods derived from the EDI and SPI-3, -6, and -12 values for each of the extreme precipitation categories: moderately wet, severely wet, extremely wet to moderately dry, and severely dry. Over four decades, the FS Province has generally experienced a suite of extreme precipitation categories ranging from moderately wet, severely wet, extremely wet to moderately dry, severely dry, and extremely dry conditions. Overall, the present study contributes towards implementation of effective drought early warning systems and can be used to enhance drought related policy and decision making in support of water resource management and planning in the FS Province.

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Drought Monitoring Using Rainfall, Evapotranspiration and Streamflow Data: A Case Study of Kaduna River Catchment Area (Nigeria)

Journal of Scientific Research and Reports ◽

10.9734/jsrr/2020/v26i830303 ◽

2020 ◽

pp. 133-144

Author(s):

A. Dare ◽

E. J. Zakka ◽

Maikano Samson ◽

A. O. Afolabi ◽

S. O. Okechalu ◽

...

Keyword(s):

Catchment Area ◽

Drought Index ◽

Meteorological Data ◽

Standardized Precipitation Index ◽

Hydrological Drought ◽

Crop Damage ◽

Drought Monitoring ◽

Drought Indices ◽

Drought Severity ◽

Drought Conditions

Drought is defined as the lack of adequate precipitation, either rain or snow that causes reduced soil moisture or groundwater, diminished streamflow, crop damage and a general water shortage. The objective of this study focuses on meteorological and hydrological drought monitoring in river Kaduna catchment area. Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) drought indices were used to characterize meteorological drought while Streamflow Drought Index (SDI) was used for hydrological drought monitoring for a period of 34 years (1967 – 2001). DrinC software, a drought indices calculator, was used for the calculation of SPI, RDI, and SDI respectively. The drought severity classification based on meteorological and hydrological drought indices gave 33% and 37% drought conditions period with the year 1967 – 2001. Based on these indexes, the drought characteristics of the catchment area were investigated by analyzing meteorological data from 1967 to 2001. The results of this analysis show that more non-drought/normal conditions were predominant than drought conditions. During the period under study (34 years), only one-year return period of extreme drought condition.

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