Development of a Demand Driven Hydro-climatic Model for Drought Planning

In recent years, droughts with increasing severity and frequency have been experienced around the world due to climate change effects. Water planning and management during droughts needs to deal with water demand variability, uncertainties in streamflow prediction, conflicts over water resources allocation, and the absence of necessary emergency schemes in drought situations. Reservoirs could play an important role in drought mitigation; therefore, development of an algorithm for operation of reservoirs in drought periods could help to mitigate the drought impacts by reducing the expected water shortages. For this purpose, the probable drought’s characteristics and their variations in response to factors such as climate change should be incorporated. This study aims at developing a contingency planning scheme for operation of reservoirs in drought periods using hedging rules with the objective of decreasing the maximum water deficit. The case study for evaluation of the performance of the proposed algorithm is the Sattarkhan reservoir in the Aharchay watershed, located in the northwestern part of Iran. The trend evaluations of the hydro-climatic variables show that the climate change has already affected streamflow in the region and has increased water scarcity and drought severity. To incorporate the climate change study in reservoir planning; streamflow should be simulated under climate change impacts. For this purpose, the climatic variables including temperature and precipitation in the future under climate change impacts are simulated using downscaled GCM (General Circulation Model) outputs to derive scenarios for possible future drought events. Then a hydrological model is developed to simulate the river streamflow, based on the downscaled data. The results show that the proposed methodology leads to less water deficit and decreases the drought damages in the study area.     

Assessment of Hydrological Drought Revisited

A variety of indices for characterising hydrological drought have been devised which, in general, are data demanding and computationally intensive. On the contrary, for meteorological droughts very simple and effective indices such as the Standardised Precipitation Index (SPI) have been used. A methodology for characterising the severity of hydrological droughts is proposed which uses an index analogous to SPI, the Streamflow Drought Index (SDI). Cumulative streamflow is used for overlapping periods of 3, 6, 9 and 12 months within each hydrological year. Drought states are defined which form a non-stationary Markov chain. Prediction of hydrological drought based on precipitation is also investigated. The methodology is validated using reliable data from the Evinos river basin (Greece). It can be easily applied within a Drought Watch System in river basins with significant storage works and can cope with the lack of streamflow data.     

Hydrological Drought Class Transition Using SPI and SRI Time Series by Loglinear Regression

Loglinear models for three-dimensional contingency tables was used with data from 21 rainfall stations and 7 hydrometric stations in the Luanhe river basin, northeast China, for short term prediction of drought severity class. Loglinear models were fitted to drought class transitions derived from standardized precipitation index (SPI) and standardized runoff index (SRI) time series to find which series was more suitable for hydrological drought class prediction 1 and 2 months ahead, respectively. Expected frequencies for two consecutive transitions between drought classes were first calculated, and based on this the predicted drought classes 1 and 2 months ahead were obtained. The results showed that despite the contingency tables of drought class transitions presented the maintenance of the precedent drought class, results of three-dimensional loglinear modeling presented good results when comparing predicted and observed drought classes. Only for a few cases predictions did not fully match the observed drought class, mainly for 2-month lead and when the SRI values are near the limit of the severity class predicted by SRI time series. Based on the correlation analysis of SPI and SRI, we presented the well-known method of hydrological drought class prediction by SPI time series. It was found that, using loglinear regression method, the accuracy of predictions for 2-month lead predicted by SPI time series was higher than those predicted by SRI time series. When we divided the SPI and SRI time series into 2 sub-periods (pre- and post-1980 where land cover changed), we got the same drought class prediction as that predicted by the entire SPI and SRI time series, which illustrated that changes in land use did not affect predictions of hydrological drought classes in the Luanhe river basin. It could be concluded that loglinear prediction of drought class transitions is a useful tool for short term hydrological drought warning, and the results could provide significant information for water resources managers and policy makers to mitigate drought effects.     

Drought Analysis in the Awash River Basin,Ethiopia

This study analyzes drought characteristics in the Awash River Basin of Ethiopia based on meteorological and hydrological variables. Standardized precipitation index is used for temporal and spatial analyses of meteorological drought and the theory of runs is used to define hydrological drought by considering streamflow as the drought indicator. Drought severity maps are generated using Arc View/GIS by summarizing the percentage of occurrence of droughts in areas within the study basin. Extreme drought category on 12-month time scale indicated that extreme events occur most frequently in the Upper and Middle Awash Basin. However, while considering the overall categories of drought, the most frequent droughts occurred in the Middle and Lower Awash Basin during the period of analysis. Similarly, results based on hydrological drought analysis shows that the severest drought events occurred in the Middle Awash Basin during May 1988 to June 1988 and April 1998 to May 1998. Analysis of the relationship between meteorological and hydrological drought indices in the basin shows that occurrence of hydrological drought event at Melka Sedi stream gauging station lags meteorological drought event in the Upper Awash on average by 7 months with a variation of 3 to 13 months.     

Drought Monitoring by Reconnaissance Drought Index (RDI) in Iran

Drought is one of the most important natural hazards in Iran and frequently affects a large number of people, causing tremendous economic losses, environmental damages and social hardships. Especially, drought has a strong impact on water resources in Iran. This situation has made more considerations toward the study and management of drought. The present study is focused on two important indices; SPI and RDI, for 3, 6, 9, 12, 18 and 24 months time scales in 40 meteorological synoptic stations in Iran. In the case of RDI computation, potential evapotranspiration was an important factor toward drought monitoring. So, evapotranspiration was calculated by Penman-Monteith equation. The correlation of RDI and SPI was also surveyed. Drought severity maps for SPI and RDI were also presented in the driest year (1999–2000). The present results have shown that the correlation of SPI and RDI was more considerable in the 3, 6 and 9 months than longer time scales. Furthermore, drought severity maps have shown that during 1999–2000, the central, eastern and south-eastern parts of Iran faced extremely dry conditions. While, according to SPI and RDI trends, other parts of the country suffered from severe drought. The SPI and RDI methods showed approximately similar results for the effect of drought on different regions of Iran. Since, RDI resolved more climatic parameters, such as evapotranspiration, into account which had an important role in water resource losses in the Iranian basins, it was worthwhile to consider RDI in drought monitoring in Iran, too.     

Comparative evaluation of impacts of climate change and droughts on river flow vulnerability in Iran

Rivers in arid and semi-arid regions are threatened by droughts and climate change. This study focused on a comparative evaluation of the impacts of climate change and droughts on the vulnerability of river flows in three basins with diverse climates in Iran. The standardized precipitation-evapotranspiration index (SPEI) and precipitation effectiveness variables (PEVs) extracted from the conjunctive precipitation effectiveness index (CPEI) were used to analyze the drought severity. To investigate hydrological droughts in the basins, the normalized difference water index (NDWI) and the streamflow drought index (SDI) were calculated and compared. The effects of droughts were assessed under various representative concentration pathway (RCP) scenarios. Changes in the number of wet days and precipitation depth restricted hydrological droughts, whereas an increasing number of dry days amplified their severity. The projected increases in dry days and precipitation over short durations throughout a year under future climate scenarios would produce changes in drought and flood periods and ultimately impact the frequency and severity of hydrological droughts. Under RCP 4.5, an increase in the frequencies of moderate and severe meteorological/hydrological droughts would further affect the Central Desert Basin. Under RCPs 2.6 and 8.5, the frequencies of severe and extreme droughts would increase, but the drought area would be smaller than that under RCP 4.5, demonstrating less severe drought conditions. Due to the shallow depths of most rivers, SDI was found to be more feasible than NDWI in detecting hydrological droughts.     

人类活动影响下塔里木河流域气象干旱向水文干旱传播的规律

为了解人类活动影响下塔里木河流域气象干旱向水文干旱传播的规律,基于标准化降水指数(SPI)和径流干旱指数(SDI)分析了气象、水文干旱的变化特征,探讨了人类活动对气象干旱向水文干旱传播规律的影响。研究结果表明：源流区气象、水文干旱均呈减弱趋势,干流气象干旱呈减弱趋势,水文干旱与之相反;随时间尺度增大,干旱历时延长;源流区气象、水文干旱以及干流气象干旱的发生频率受人类活动影响后(1993年后)均降低,仅干流水文干旱的发生频率升高;受人类活动影响后,源流区不同季节气象干旱向水文干旱的传播时间均变长,干流干旱传播时间除春季外均缩短;源流区干旱传播时间延长与气候变化有关,而干流干旱传播时间缩短主要是受人类活动的影响。     

Assessment of future climate change impacts on hydrological behavior of Richmond River Catchment

This study evaluated the impacts of future climate change on the hydrological response of the Richmond River Catchment in New South Wales (NSW), Australia, using the conceptual rainfall-runoff modeling approach (the Hydrologiska Byrans Vattenbalansavdelning (HBV) model). Daily observations of rainfall, temperature, and streamflow and long-term monthly mean potential evapotranspiration from the meteorological and hydrological stations within the catchment for the period of 1972–2014 were used to run, calibrate, and validate the HBV model prior to the streamflow prediction. Future climate signals of rainfall and temperature were extracted from a multi-model ensemble of seven global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 3 (CMIP3) with three regional climate scenarios, A2, A1B, and B1. The calibrated HBV model was then forced with the ensemble mean of the downscaled daily rainfall and temperature to simulate daily future runoff at the catchment outlet for the early part (2016–2043), middle part (2044–2071), and late part (2072–2099) of the 21st century. All scenarios during the future periods present decreasing tendencies in the annual mean streamflow ranging between 1% and 24.3% as compared with the observed period. For the maximum and minimum flows, all scenarios during the early, middle, and late parts of the century revealed significant declining tendencies in the annual mean maximum and minimum streamflows, ranging between 30% and 44.4% relative to the observed period. These findings can assist the water managers and the community of the Richmond River Catchment in managing the usage of future water resources in a more sustainable way.     

云南2009—2014年持续性气象水文干旱特征及成因分析

基于戴-帕尔默干旱强度指数(Dai Palmer drought severity index,Dai-PDSI)和径流干旱指数(streamflow drought index,SDI),分析云南地区2009—2014年持续性气象干旱与水文干旱时空演变特征,并利用NCAR/NCEP再分析资料,从西太平洋副热带高压、青藏高压、南支槽、对流层垂直运动及水汽垂直分布等视角,分析2009—2014年云南持续性干旱的原因。结果表明:(1)2009—2014年是云南地区自1961年以来最严重的一次持续性极端干旱过程,2009年10月—2010年9月是最干旱的时段;夏季与冬季是干旱最严重的两个季节。(2)在空间上,云南中东部旱情最重,东南部稍轻。(3)水文干旱伴随气象干旱而生,金沙江和南盘江出现重度水文干旱,澜沧江出现中等水文干旱,从强度上讲,水文干旱弱于气象干旱。(4)夏季西太平洋副热带高压偏西偏强,青藏高压持续偏强、中心偏西,云南上空的大气持续受它们控制,盛行下沉气流;冬季南支槽偏弱,不利于引导孟加拉湾水汽北上;在其他季节,大气多以下沉运动为主,对流层水汽严重不足。     

滦河流域气象干旱向水文干旱传播特征及风险分析

干旱是一种复杂的自然灾害,气象干旱可能导致水文干旱等灾害,严重影响社会经济发展。探明气象干旱向水文干旱传播的特征及规律,可为减小干旱损失、保障流域供水用水安全提供技术支持。本文基于滦河山区1960—2017年的气象水文数据,应用游程原理识别气象水文干旱事件,甄别二者间的传播特征,并借助Copula模型评估气象干旱向水文干旱的风险和干旱传播的临界关系。结果表明：（1）在1960—2017年期间,与气象干旱事件相比,水文干旱事件具有频率低、历时长、峰值低的特点;（2）滦河地区气象干旱和水文干旱传播关系以单场气象干旱向单场水文干旱传播为主;（3）气象干旱向水文干旱的传播存在明显的滞后效应,从上游至下游地区干旱滞后时间依次增长;（4）Gumbel Copula函数能够更准确地评估该流域干旱传播风险,结果显示上游地区发生干旱传播的风险低于下游地区,上、下游地区气象干旱发展成水文干旱的临界历时分别为0.93个月和1.26个月,临界峰值强度分别为0.66和0.44。本研究可为评价不同干旱事件间的传播与演变关系,构建流域干旱风险评价模型提供新思路。     

A New Method for Joint Frequency Analysis of Modified Precipitation Anomaly Percentage and Streamflow Drought Index Based on the Conditional Density of Copula Functions

In this study, a new method was proposed to model the occurrence of related variables based on the conditional density of copula functions. The proposed method was adopted to investigate the dynamics of meteorological and hydrological droughts in the Zarinehroud basin, southeast of Lake Urmia, during the period 1994–2015. For this purpose, the modified precipitation anomaly percentage and streamflow drought indices were extracted. Finally, the joint frequency analysis of duration-duration and severity-severity characteristics of meteorological and hydrological droughts was analyzed. Analysis of 7 different copulas used to create the joint distribution in the Zarinehroud basin indicated that the Frank copula had the best performance in describing the relationship between the meteorological and hydrological drought severities and durations. By examining the results of the bivariate analysis of duration-duration of meteorological and hydrological droughts at different stations, the expected meteorological and hydrological drought durations were estimated in the years ahead. For example, at Chalkhmaz station, 4- to 7-month duration for the hydrological drought and 9- to 12-month duration for the meteorological drought is expected in the years ahead. The joint frequency analysis of drought characteristics allows to determine the meteorological and hydrological drought characteristics at a single station at the same time using joint probabilities. Also, the results indicated that by knowing the conditional density, the hydrological drought characteristics can be easily estimated for the given meteorological drought characteristics. This could provide users and researchers useful information about the probabilistic behavior of drought characteristics for optimal operation of surface water.

     

Adaptation Strategy to Mitigate the Impact of Climate Change on Water Resources in Arid and Semi-Arid Regions: a Case Study

Climate change and drought phenomena impacts have become a growing concern for water resources engineers and policy makers, mainly in arid and semi-arid areas. This study aims to contribute to the development of a decision support tool to prepare water resources managers and planners for climate change adaptation. The Hydrologiska Byråns Vattenbalansavdelning (The Water Balance Department of the Hydrological Bureau) hydrologic model was used to define the boundary conditions for the reservoir capacity yield model comprising daily reservoir inflow from a representative example watershed with the size of 14,924 km² into a reservoir with the capacity of 6.80 Gm³. The reservoir capacity yield model was used to simulate variability in climate change-induced differences in reservoir capacity needs and performance (operational probability of failure, resilience, and vulnerability). Owing to the future precipitation reduction and potential evapotranspiration increase during the worst case scenario (?40% precipitation and +30% potential evapotranspiration), substantial reductions in streamflow of between ?56% and ?58% are anticipated for the dry and wet seasons, respectively. Furthermore, model simulations recommend that as a result of future climatic conditions, the reservoir operational probability of failure would generally increase due to declined reservoir inflow. The study developed preparedness plans to combat the consequences of climate change and drought.     

Hydrological Responses to Climate Change in Nenjiang River Basin,Northeastern China

Under the background of global climate change, hydrological responses to climate change were investigated in Northeastern China. This study analyses the trends of annual and seasonal temperature, precipitation and streamflow series in Nenjiang River Basin. Correlations between streamflow and meteorological variables were investigated, while parametric method and nonparametric tests were applied to determine the trends and correlations. Data collected from a series of monitoring stations showed significant increasing trends of annual and seasonal mean temperature versus time, whereas during the whole period the annual and seasonal precipitation in the basin did not exhibit similar trends although temporal and spatial variations were detected. Affected by the precipitation and temperature changes, significant trends of decreasing annual, spring and autumn streamflow were demonstrated; the decrease concentrating mainly on the mainstream and tributaries of the left bank. Correlation analyses revealed strong relationships between the streamflow and meteorological variables in Nenjiang River Basin, and the impacts of climate change on streamflow were complicated. Results from this study will help water resource managers for decision makings that address the consequences of climate change.     

关中地区气象水文综合干旱指数及干旱时空特征

根据陕西关中地区22个气象站和3个水文站1961—2016年的气象水文资料,计算了不同时间尺度的标准化降水蒸散发指数(SPEI)与径流干旱指数(SDI),运用Gumbel Copula函数构建了气象水文综合干旱指数(MHDI),探讨了MHDI的适用性,并分析了气象水文综合干旱时空分布特征。结果表明:MHDI综合了SPEI与SDI的优点,可同时表征月尺度和年尺度的气象干旱与水文干旱;关中地区MHDI序列值有明显的下降趋势,干旱情况逐年加剧;MDHI序列存在变异,年尺度变异点集中于1986年和1990年;年尺度的序列值主周期多集中在20～22 a;泾河流域干旱发生频率最低,为19.11%,北洛河流域干旱发生频率最高,为47.97%,渭河流域干旱发生频率介于两者之间,为26.42%。     

Hydro-Climatological Drought Analyses and Projections Using Meteorological and Hydrological Drought Indices: A Case Study in Blue River Basin, Oklahoma

Understanding the characteristics of historical droughts will benefit water resource managers because it will reveal the possible impacts that future changes in climate may have on drought, and subsequently, the availability of water resources. The goal of this study was to reconstruct historical drought occurrences and assess future drought risk for the drought-prone Blue River Basin in Oklahoma, under a likely changing climate using three types of drought indices, i.e., Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI) and Standardized Runoff Index (SRI). No similar research has been conducted in this region previously. Monthly precipitation and temperature data from the observational period 1950?C1999 and over the projection period 2010?C2099 from 16 statistically downscaled Global Climate Models (GCM) were used to compute the duration, severity, and extent of meteorological droughts. Additionally, soil moisture, evapotranspiration (ET), and runoff data from the well-calibrated Thornthwaite Monthly Water Balance Model were used to examine drought from a hydrological perspective. The results show that the three indices captured the historical droughts for the past 50?years and suggest that more severe droughts of wider extent are very likely to occur over the next 90?years in the Blue River Basin, especially in the later part of the 21st century. In fact, all three indices display lower minimum values than those ever recorded in the past 50?years. This study also found that SRI and SPI (PDSI) had a correlation coefficient of 0.81 (0.78) with a 2-month (no appreciable) lag time over the 1950?C2099 time period across the basin. There was relatively lower correlation between SPI and PDSI over the same period. Although this study recommends that PDSI and SRI are the most suitable indices for assessing future drought risks under an increasingly warmer climate, more drought indices from ecological and socioeconomic perspectives should be investigated and compared to provide a complete picture of drought and its potential impacts on the dynamically coupled nature-human system.     

Linking Drought Indicators to Policy Actions in the Tagus Basin Drought Management Plan

One crucial aspect of drought management plans is to establish a link between basin drought state and management actions. Basin state is described by a drought indicator system that includes variables like precipitation, streamflow, reservoir inflow, reservoir storage and groundwater piezometric levels. Basin policy consists on a catalogue of management actions, ranging from enforcing demand reduction strategies to establishing priority of users to allocate scarce water or approving emergency works. In this paper, the methodology applied in the Tagus Basin Drought Management Plan to link operational drought indicators to policy actions in regulated water supply systems is presented. The methodology is based on the evaluation of the probability of not being able to satisfy system demands for a given time horizon. A simplified model of every water resources system in the basin was built to evaluate the threshold of reservoir volume that is required to overcome the drought situation without deficit. For each reservoir level, a set of policy actions is proposed with the goal of guaranteeing essential demands during drought conditions. The methodology was validated with a simulation of system behavior for 60 years of historic streamflow series, finding acceptable results in most systems.     

Analysis of Drought from Humid,Semi-Arid and Arid Regions of India Using DrinC Model with Different Drought Indices

The study aims at evaluating the various drought indices for the humid, semi-arid and arid regions of India using conventional indices, such as rainfall anomaly index, departure analysis of rainfall and other indices such as Standard Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) that were analyzed using the DrinC software. In SPI, arid region has seven drought years, whereas humid and semi-arid regions have four. In case of RDI, the humid and semi-arid regions have 11 drought years, whereas arid regions have 10 years. The difference in SPI and RDI was due to the fact that RDI considered potential evapotranspiration, and hence, correlation with plants would be better in case of RDI. Humid region showed a decreasing trend in initial value of RDI during the drought as compared to semiarid and arid regions and indicated possible climate change impact in these regions. Among all the indices, RDI was considered as an effective indicator because of implicit severity and high prediction matches with the actual drought years. SPI and RDI were found to be well correlated with respect to 3 months rainfall data and SPI values led to prediction of annual RDI. The results of our study established that this correlation could be used for developing disaster management plan well in advance to combat the drought consequences.

     

Trend Detection of Drought in Arid and Semi-Arid Regions of Iran Based on Implementation of Reconnaissance Drought Index (RDI) and Application of Non-Parametrical Statistical Method

Drought is known as one of the main natural hazards especially in arid and semi-arid regions where there are considerable issues in regard to water resources management. Also, climate changes has been introduced as a global concern and therefore, under conditions of climate change and global warming, the investigation of drought severity trend in regions such as Iran which is mainly covered by arid and semi-arid climate conditions is in the primary of importance. Therefore, in this study, based on the application of Reconnaissance Drought Index (RDI) for assessment drought severities, and also the implementation of non-parametric Mann- Kendall statistics and Sen’s slope estimator, the trends in different time series of RDI (3, 6, 9, 12, 18 and 24 monthly time series) were investigated. Results indicated the frequent decreasing trends in RDI time series particularly for long term time series (12, 18 and 24 monthly time series) than short term ones. Decreasing trend in RDI time series means the increasing trend in drought severities. Since the water resources especially ground water in most cases are affected by long term droughts, therefore, increasing trend in drought intensities in long term ones can be a threat for water resources management in surveyed areas.     

Multivariate Drought Assessment Considering the Antecedent Drought Conditions

Several drought indices have been developed based on a single variable or multiple variables using very complex calculations. Antecedent conditions are quite significant for analyzing physical processes involved in the conceptual rainfall-runoff modeling and for proper assessment of drought. However, not much attention has been paid to these conditions in the development of drought indices. Hence, we developed an alternative index for drought assessment, i.e., the antecedent condition-based multivariate drought index (AMDI), by taking into consideration all of the forms of drought, including meteorological, agricultural, and hydrological drought, in combination with the antecedent drought conditions. By comparing the AMDI with the standardized precipitation index (SPI) and reconnaissance drought index (RDI), it was revealed that in most cases, the drought trend was more or less the same. However, some discrepancies were also observed. Moreover, by considering additional factors, i.e., the antecedent soil moisture conditions and balance, an approximately 6 % difference in the drought frequency was observed compared to that of the SPI and RDI results, leading to a significant and proper drought assessment. The AMDI was also identified as a multi-scalar, multivariate index, which aggregates the effects of multiple drought forms by maintaining the continuity during month-to-month transitions. Hence, we concluded that the AMDI could be considered as an alternative tool for significant drought assessment.     

Past and Future Global Drought Assessment

Water Resources Management - Understanding the climate change impacts on drought occurrence is of great importance for comprehensive water resources management. Reconnaissance drought index (RDI)...