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.

     

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.     

Drought Characterisation Based on Water Surplus Variability Index

Drought assessment, characterisation and monitoring increasingly requires considering not only precipitation but also the other meteorological parameters such as an evapotranspiration. Thus, some new drought indices based on precipitation and evapotranspiration have been developed. This study introduces a new drought index named the water surplus variability index (WSVI). The procedure to estimate the index involves accumulation water surplus at different time scales. To approve the proposed procedure, the WSVI is compared with the standardized precipitation index (SPI), the reconnaissance drought index (RDI) and the standardized precipitation evapotranspiration index (SPEI) based on 1-, 3-, 6- and 12-month timescales using data from several weather stations located in regions with different aridity index. Near perfect agreement (d?~?1) between WSVI and SPI, RDI and SPEI was indicated in humid and sub-humid locations. The results also showed that the correlation coefficients between WSVI and SPI, RDI and SPEI were higher for semi-arid stations than for arid ones.     

Effect of Air Temperature on Historical Trend of Long-Term Droughts in Different Climates of Iran

Effective monitoring of drought plays an important role in water resources planning and management, especially under global warming effect. The aim of this paper is to study the effect of air temperature on historical long-term droughts in regions with diverse climates in Iran. To this end, monthly air temperature (T) and precipitation (P) data were gathered from 15 longest record meteorological stations in Iran covering the period 1951–2014. Long-term meteorological droughts behavior was quantified using two different drought indices, i.e. the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). Linear and non-linear trends in T, P, SPI and SPEI were evaluated using non-parametric and parametric statistical approaches such as non-modified and modified Mann-Kendall Test, Theil-Sen approach, and simple regression. The results indicated that the significant trends for temperature are approximately all increasing (0.2 °C to 0.5 °C per decade), and for precipitation are mostly decreasing (?7.2 mm to ?14.8 mm per decade). It was also indicated that long-term drought intensities monitored by the SPI and SPEI have had significant downward trend (drought intensification with time) at most stations of interest. The observed trends in the SPI series can be worsen if air temperature (in addition to precipitation) participates in drought monitoring as SPEI. In arid and extra arid climates, it was observed that temperature has strong effects on historical drought characteristics when comparing the SPI and SPEI series. Due to the determinative role of temperature in mostly dry regions like Iran, the study suggests using the SPEI rather than SPI for more effective monitoring of droughts.     

Spatial and Time Variability of Drought Based on SPI and RDI with Various Time Scales

The spatial and temporal variability of droughts were studied for the Northeast Algeria using SPI and RDI computed with monthly precipitation data from 123 rainfall stations and CFSR reanalysis monthly temperature data covering the period 1979–80 to 2013–14. The gridded temperature data was interpolated to all the locations having precipitation data, thus providing to compute SPI and RDI with the time scales of 3-, 6- and 12-month with the same observed rainfall data. Spatial and temporal patterns of droughts were obtained using Principal Component Analysis in S-Mode with Varimax rotation applied to both SPI and RDI. For all time scales of both indices, two principal components were retained identifying two sub-regions that are similar and coherent for all SPI and RDI time scales. Both components explained more than 70% and 74% of drought spatial variability of SPI and RDI, respectively. The identified sub-regions are similar and coherent for all SPI and RDI time scales. The Modified Mann-Kendall test was used to assess trends of the RPC scores, which have shown non-significant trends for decreasing drought occurrence and severity in both identified drought sub-regions and all time scales. Both indices have shown a coherent and similar behavior, however with RDI likely showing to identify more severe and moderate droughts in the southern and more arid sub-region which may be due to its ability to consider influences of global warming. Results for RDI are quite uniform relative to time scales and show smaller differences among the various climates when compared with SPI. Further assessments covering the NW and NE of Algeria using longer time series should be performed to better understand the behavior of both indices.     

基于SPEI的南水北调中线水源区干旱时空特征

利用多种统计方法对南水北调中线水源区降水和气温序列进行趋势诊断,识别了不同气象站点序列的时空变化趋势;以标准化降水蒸散指数(SPEI)为干旱指标,建立考虑降水和气温共同对干旱过程影响的评价模型,研究分析了水源区不同时间尺度和分期(汛期、非汛期和全年期)干旱过程动态变化特征。分析表明:降水量呈现不显著的下降趋势,气温总体呈现显著性上升趋势;短时间尺度SPEI对降水和气温变化更加敏感,随着时间尺度增大,SPEI值变化更加平缓;非汛期和全年期水源区发生严重干旱的概率增大,不同气象站点3个不同时期发生特旱或重旱的年份与历史发生干旱的资料相一致;干旱严重程度从上游到下游逐渐衰减,整个汉江上游和西北部地区干旱发生频次略高于下游和南部地区;对比标准化降水指标(SPI)计算结果,SPEI指数较SPI指数补充考虑了降水和气温对干旱过程的综合影响,可作为SPI指数的一个重要补充分析手段,可应用于描述南水北调中线水源区不同时间尺度的干旱特征。     

Comparing SPI and RDI Applied at Local Scale as Influenced by Climate

Drought and wetness events were studied in the Northeast Algeria with SPI and RDI. The study area includes a variety of climatic conditions, ranging from humid in the North, close to the Mediterranean Sea, to arid in the South, near the Sahara Desert. SPI only uses precipitation data while RDI uses a ratio between precipitation and potential evapotranspiration (PET). The latter was computed with the Thornthwaite equation, thus using temperature data only. Monthly precipitation data were obtained from 123 rainfall stations and monthly temperature data were obtained from CFSR reanalysis gridded temperature data. Both data sets cover the period 1979–80 to 2013–14. Using ordinary kriging, the gridded temperature data was interpolated to all the locations having precipitation data, thus providing to compute SPI and RDI with the same observed rainfall data for the 3-, 6- and 12-month time scales. SPI and RDI were therefore compared at station level and results and have shown that both indices revealed more sensitive to drought when applied in the semi-arid and arid zones. Differently, more wetness events were detected by RDI in the more humid locations. Comparing both indices, they show a coherent and similar behavior, however RDI shows smaller differences among climate zones and time-scales, which is an advantage relative to the SPI and is likely due to including PET in RDI.     

Long-Term Climatic Variability in Calabria and Effects on Drought and Agrometeorological Parameters

In recent decades a general change in climate has been documented in several locations over the world. Such changes could have significant effects on various environmental scenarios, including water resource management, agriculture, hydrology and ecosystems. The complex topography and coastlines of Mediterranean regions influences the climatic regime exhibiting substantial fine-scale spatial variability. In Italy, the climate is generally becoming warmer and drier, with quite large differences depending on the site and data treatment. In this study a historical set of meteorological data (110 precipitation and 28 temperature series), collected over 1921–2007 in the Calabria region (Southern Italy) was analysed. Several meteorological and agrometeorological indices were selected for whether they could evaluate the potential effects of climate change on water availability for natural vegetation and cultivated plants. The significance of the analysed time series (monthly, seasonal and annual time scales) was evaluated by using statistical trend analysis (Mann-Kendall and t-test). Moreover, the intensities of drought events were determined using the Standardized Precipitation Index (SPI) for the time scales of 3 and 6 months. The analysis highlighted a general decrease in annual precipitation and an increase in drought intensity. At a regional level, yearly precipitation decreased by almost 318 mm/100 years (representing almost 30 % of the yearly mean precipitation in the region). Temperature changes were more complex. On a regional scale, yearly mean minimum temperatures increased by 0.9 °C/100 years and maximum and mean temperatures decreased by 1 °C/100 years and 0.8 °C/100 years, respectively. Due to the asymmetric behaviour of temperatures, there was a decreasing impact on evapotranspiration.     

Regional Drought Assessment Based on the Reconnaissance Drought Index (RDI)

Regional drought assessment is conventionally based on drought indices for the identification of drought intensity, duration and areal extent. In this study, a new index, the Reconnaissance Drought Index (RDI) is proposed together with the well known Standardized Precipitation Index (SPI) and the method of deciles. The new index exhibits significant advantages over the other indices by including apart from precipitation, an additional meteorological parameter, the potential evapotranspiration. The drought assessment is achieved using the above indices in two river basins, namely Mornos and Nestos basins in Greece. It is concluded that although the RDI generally responds in a similar fashion to the SPI (and to a lesser extent to the deciles), it is more sensitive and suitable in cases of a changing environment.     

Projected Changes of Future Extreme Drought Events under Numerous Drought Indices in the Heilongjiang Province of China

Effective drought prediction methods are essential for the mitigation of adverse effects of severe drought events. This study utilizes the Reconnaissance Drought Index, Standardized Precipitation Index and Standardized Precipitation Evapotranspiration Index to assess the occurrence of future drought events in the study area of the Heilongjiang province of China over a period of 2016–2099. The drought indices were computed from the meteorological data (temperature, precipitation) generated by the global climate model (HadCM3A2). Moreover, Mann-Kendall trend test was applied for the assessment of future climatic trends and detecting probable differences in the behaviour of various drought indices. Drought forecasting periods has been divided into three categories: the early phase (1916–2030), middle phase (2031–2060) and late phase (2061–2099). The occurrence of future droughts is also ranked according to their intensity (mild, moderate, severe and extreme drought). Based on the drought results, more number of drought events are expected to occur during 12-month drought analysis are, RDI during 2084–2098 (DD = 14, DS = ?1.38), SPEI during 2084–2098 (DD = 14, DS = ?1.33) and SPI during 2084–2095 (DD = 12, DS = ?1.19). The 1st and 2nd months of the years studied predicted a warming trend, while the 7th, 8th, and 9th months predicted a wetter trend. Finally, it was observed that RDI is more sensitive to drought and indicated a high percentage of years under severe and extreme drought conditions during the drought frequency analysis. Conclusively, this study provides a strategies for water resources management and monitoring of droughts, in which drought indices like RDI can play a central role.     

Climate Variability Impact on the Spatiotemporal Characteristics of Drought and Aridityin Arid and Semi-Arid Regions

Investigating the spatiotemporal distribution of climate data and their impact on the allocation of the regional aridity and meteorological drought, particularly in semi-arid and arid climate, it is critical to evaluate the climate variability effect and propose sufficient adaptation strategies. The coefficient of variation, precipitation concentration index and anomaly index were used to evaluate the climate variability, while the Mann-Kendall and Sen’s slope were applied for trend analysis, together with homogeneity tests. The aridity was evaluated using the alpha form of the reconnaissance drought index (Mohammed & Scholz, Water Resour Manag 31(1):531–538, 2017c), whereas drought episodes were predicted by applying three of the commonly used meteorological drought indices, which are the standardised reconnaissance drought index, standardized precipitation index and standardized precipitation evapotranspiration index. The Upper Zab River Basin (UZRB), which is located in the northern part of Iraq and covers a high range of climate variability, has been considered as an illustrative basin for arid and semi-arid climatic conditions. There were general increasing trends in average temperature and potential evapotranspiration and decreasing trends in precipitation from the upstream to the downstream of the UZRB. The long-term analysis of climate data indicates that the number of dry years has temporally risen and the basin has experienced succeeding years of drought, particularly after 1994/1995. There was a potential link between drought, aridity and climate variability. Pettitt’s, SNHT, Buishand’s and von Neumann’s homogeneity test results demonstrated that there is an evident alteration in the mean of the drought and aridity between the pre- and post-alteration point (1994).

     

Development of Drought Indices for Semi-Arid Region Using Drought Indices Calculator (DrinC) – A Case Study from Madurai District,a Semi-Arid Region in India

Drought is considered as a major natural hazard/ disaster, affecting several sectors of the economy and the environment worldwide. Drought, a complex phenomenon can be characterised by its severity, duration, and areal extent. Drought indices for the characterization and the monitoring of drought simplify the complex climatic functions and can quantify climatic anomalies for their severity, duration, and frequency. With this as background drought indices were worked out for Madurai district of Tamil Nadu using DrinC (Drought Indices Calculator) software. DrinC calculates the drought indices viz., deciles, Standard Precipitation Index (SPI), Reconnaissance Drought Index (RDI), Streamflow Drought Index (SDI) by providing a simple, though flexible interface by considering all the factors. The drought of 3, 6 and 9 months as time series can also be estimated. The results showed that drought index of Madurai region by decile method revealed that among the 100 years, 20 years were affected by drought and it is cyclic in nature and occurring almost every 3 to 7 years once repeatedly, except for some continuous period, i.e., 1923, 1924 and 1985, 1986, etc. During the last five decades, the incidence is higher with 13 events, whereas in the first five decades it was only 7. The SPI and RDI index also followed the similar trend of deciles. However, under SPI and RDI, the severely dry and extremely dry category was only seven years and all other drought years of deciles were moderately dry. Our study indicated that SPI is a better indicator than deciles since here severity can be understood. SDI did not follow the trend similar to SPI or RDI. Regression analysis showed that the SPI and RDI are significantly correlated and if 1st 3 months rainfall data is available one can predict yearly RDI drought index. The results demonstrated that these approaches could be useful for developing preparedness plan to combat the consequences of drought. Findings from such studies are useful tools for devising strategic preparedness plans to combat droughts and mitigate their effects on the activities in the various sectors of the economy.     

基于SPI指标左江流域旱涝演变规律与趋势预测分析

为探明广西驮英灌区旱涝灾害演变机理,揭示旱涝的演变规律,选取了1983年～2018年该灌区及周边5座大中型水库的逐月降水量数据,采用标准化降水指数SPI法对降雨数据进行不同时间尺度的处理,以SPI指数表征区域历史旱涝程度,采用趋势分析并运用Morlet小波分析方法,分析灌区近年旱涝变化的周期性,预测未来旱涝变化趋势。结果表明,该灌区年降水量变化波动幅度较大,年降水呈不显著的增长趋势;降水量具有明显的阶段性特征;年降水主要分布在汛期,夏秋季节的降水过程对年降水过程影响较大。根据Morlet小波分析结果,预测未来灌区总体降水将偏多,其中春夏两季将处于丰水期,而秋冬两季将处于枯水期。     

Impacts of Multi-year Droughts and Upstream Human-Induced Activities on the Development of a Semi-arid Transboundary Basin

This paper aims at investigating the combined impacts of basin-wide multi-year droughts and upstream human-induced activities on current and future potential development of a semi-arid transboundary basin. The approach is based on the drought analysis through three widely used drought indices (Standardised Drought Index- SPI, Reconnaissance Drought Index - RDI and Streamflow Drought Index- SDI), coupled with the current and future conceivable man-made changes upstream, taking also into account the effects of climate change. As a representative case, the Diyala river basin, shared between Iraq and Iran, is selected. A close examination of the climate trends in the study area exhibits that the basin points to be drier, with a decreasein precipitation and rise in the rates of temperature and potential evapotranspiration. The comparison between RDI and SDI indicates the cumulative drought effects on runoff during recent multi-year droughts episodes (1999–2001 and 2008–2009), which crippled the socio-economic activities and influenced the environmental system. Further, the results reveal that the combined impacts of multi-year droughts at basin scale and the river damming, water abstraction and water diversion works upstream have significant effects on water availability, especially at the middle and lower parts of the basin, with impacts on the security of the irrigated agriculture and public water supply, contributing to displacement and tribal conflicts. The projected climate change conditions along with the water withdrawal schemes upstream, which will put into operation in the foreseeable future, are expected to increase the vulnerability of water security in the portion of the basin that lies in the downstream country.     

不同干旱指数在唐山地区旱情评价中的应用

基于唐山地区1957—2011年的气象资料,比较分析标准化降水指数（S SPI）、标准化降水蒸散发指数（S SPEI）和帕默尔水文干旱指数（P PHDI）3种不同干旱指数的相关性,并评价了各个指数在唐山地区连旱期间的适用性。结果表明：各时间尺度（年、季、月）的S SPI和S SPEI均显著相关;P PHDI与年尺度的S SPI和S SPEI均显著相关。P PHDI对长期干旱判断效果明显优于短期干旱。年尺度S SPEI和S SPI对干旱事件识别效果比较接近,二者对长期干旱判断偏涝,对短期干旱判断效果明显优于P PHDI。在气温偏低的年份,季尺度的S SPI能很好地反映旱情的严重程度,在气候变暖的背景下,季尺度S SPEI比S SPI更能准确地判断和评价旱情。     

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.     

基于标准化降水指数的淮河流域干旱 演变特征分析

利用淮河流域35个气象站点的降水资料,采用标准化降水指数(Standardized Drecipitafion in- dex , SP1)分析了淮河流域近50年(1961 } 2010年)的年度干旱指数,并利用干旱发生频率、干旱站次比和干旱强度三项干旱指标分析了淮河流域的干旱演变特征。研究结果表明,近50年来,淮河流域以轻旱、中旱为主,重旱、特旱相对较少,有干旱发生面积有逐年递减而发生强度呈增强趋势。在当前气候变化背景下,淮河流域干旱对农业生产的不利影响有减小的趋势。     

汉江流域植被变化及其对多时间尺度气象干旱的响应

干旱是影响植被生长的重要因素之一,因此研究植被对不同时间尺度干旱的响应具有重要意义。利用1982—2019年汉江流域逐月降水和归一化植被指数（NDVI）数据,计算得到不同时间尺度下的标准化降水指数（SPI）、植被状态指数（VCI）和植被覆盖度（FVC）,分析了植被时空变化及对多时间尺度气象干旱的响应特征。结果表明：汉江流域生长季NDVI在时间上呈现波动上升趋势,植被覆盖度在空间上表现为西高东低的分布特点;随着时间尺度的增加,干湿交替频率减小,表征干旱事件对降水的敏感性在降低;从干旱趋势来看,分别有37.62%和62.38%的地区呈现上升和下降趋势;从干旱频率来看,各季干旱高频事件集中在流域中部和东部;在年尺度下,NDVI与SPI-12在大部分地区呈负相关,有43.26%的地区表现为正相关,主要分布在流域中部和东南部;在季尺度下,春季NDVI对SPI-3的响应最明显,85.64%的地区表现为正相关;在月尺度下,汉江流域春季VCI受SPI-1和SPI-3的影响最为明显,而秋季VCI对SPI-12的响应更为显著;在不同土地利用类型中,草地和耕地与SPI的相关性较高,说明其对干旱的抵抗力较弱。     

鄱阳湖干旱多尺度特征及其与月均水位的相关性

以鄱阳湖13个气象站1957~2013年的逐月降水量、平均气温、各站点纬度和同期水位站逐月平均水位为实验数据,分别计算1、3、6、12、24、48个月尺度下标准降水指数(SPI)和标准降水蒸散指数(SPEI)时间序列,并利用Morlet小波分析理论,分析了该序列多时间尺度变化特征。基于Mann-Kendall检验,分析了鄱阳湖气象干旱趋势特征;利用Spearman秩相关系数,研究了不同时间尺度SPI和SPEI序列与月平均水位的相关关系。研究表明,鄱阳湖流域SPI和SPEI序列存在约68个月变化的主周期,两个主要特征时间尺度变化的强分布;气象干旱与湖水位的相关关系随时间尺度的增大而减弱。     

Bi-site Analysis of Meteorological Drought Duration: Theoretical Modeling and Application

Droughts are regional incidents that threat the environment and limit most of the socio-economic activities. Given the dry and wet state sequences for two sites, X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} , this paper presents a procedure to reduce the two sequences X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} to one sequence Z _t for the purpose of simplifying the analysis of drought duration at two sites jointly. Theoretical models to evaluate the expected value and the variance of the process Z _t and the occurrence probability of the dry state at two sites jointly are presented and verified using simulation experiments. Historical data for the period 1939–2005 and generated rainy season precipitation data for two gauging sites in Central Jordan, namely Amman Airport and Madaba, is used in the present study to investigate the occurrence of droughts. The joint analysis of drought duration obtained using the historical precipitation at the two sites appears to be inconsistent especially for droughts of duration longer than 3 years. On the other hand, the joint analysis of drought duration obtained theoretically by employing the characteristics of the process Z _t are found to match well with the more reliable drought statistics obtained empirically by analyzing the long generated precipitation. Considering 25 years planning horizon, droughts of 1, 2, and 3 years duration are the most frequent droughts in the region of Central Jordan. The return period of such regional droughts ranges from 8–30 years.