Investigating remote sensing indices to monitor drought impacts on a local scale (case study: Fars province,Iran)

As drought occurs in different climates, assessment of drought impacts on parameters such as vegetation cover is of utmost importance. Satellite remote sensing images with various spectral and spatial resolutions represent information about different land covers such as vegetation cover. Hence, the purpose of this study was to investigate the performance of satellite vegetation indices to monitor the agricultural drought on a local scale. In this regard, satellite images including Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR) data were used to evaluate vegetation cover and their gradual changes effects on agricultural drought. Fars province in Iran with relatively low precipitation values was selected as the study area. Modified Perpendicular Drought Index (MPDI), MPDI1, Vegetation Condition Index (VCI), Normalized Difference Vegetation Index Anomalies (NDVIA), and Standardized Vegetation Index (SVI), were evaluated to select the remote sensing based index with the best performance in drought monitoring. The performance of such indices were investigated during 13 years (2000–2013) for MODIS and 29 years (1985–2013) for AVHRR. To assess the efficiency of the satellite indices in drought investigation, Standardized Precipitation Index (SPI) data of five selected stations were used for 3, 6, and 9 month periods on August. The results showed that NDVI-based vegetation indices had the highest correlation with SPI in cold climate and long-term timescale (6 and 9 month). The highest correlation values between remote sensing based indices and SPI were acquired, respectively, in 9-month and 6-month time-scales, with the values of 43.5% and 40%. Moreover, VCI showed the highest capability for agricultural drought investigating in different climate regions of the study area. Overall, the results proved that NDVI-based indices can be used for drought monitoring and assessment in a long-term timescale on a local time-scale.

     

Analysing the relationship between drought and soil erosion using vegetation health index and RUSLE models in Godavari middle sub-basin,India

Drought is a natural phenomenon posing severe implications for soil, groundwater and agricultural yield. It has been recognized as one of the most pervasive global change drivers to affect the soil. Soil being a weakly renewable resource takes a long time to form, but it takes no time to degrade. However, the response of soil to drought conditions as soil loss is not manifested in the existing literature. Thus, this study makes a concerted effort to analyze the relationship between drought conditions and soil erosion in the middle sub-basin of the Godavari River in India. MODIS remote sensing data was utilized for driving drought indices during 2000–2019. Firstly, we constricted Temperature condition index (TCI) and Vegetation Condition Index (VCI) from Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI) derived from MODIS data. TCI and VCI were then integrated to determine the Vegetation Health Index (VHI). Revised Universal Soil Loss Equation (RUSLE) was utilized for estimating soil loss. The relationship between drought condition and vegetation was ascertained using the Pearson correlation. Most of the northern and southern watersheds experienced severe drought condition in the sub-basin during 2000–2019. The mean frequency of the drought occurrence was 7.95 months. The average soil erosion in the sub-basin was estimated to be 9.88 t ha^?1 year^?1. A positive relationship was observed between drought indices and soil erosion values (r value being 0.35). However, wide variations were observed in the distribution of spatial correlation. Among various factors, the slope length and steepness were found to be the main drivers of soil erosion in the sub-basin. Thus, the study calls for policy measures to lessen the impact of drought and soil erosion.     

Land subsidence (2004–2013) in Changzhou in Central Yangtze River delta revealed by MT-InSAR

Droughts are hindrances to economic and social developments in many parts of the world, especially in developing nations like Kenya. In North Eastern Kenya (NEK), drought is very prevalent. The communities in the region are mainly dependent on animal farming, and drought occurrence leads to great socioeconomic setback. Drought indices used in most studies consider rainfall as the only parameter for assessing drought occurrences. This study analyzes drought in NEK using the Standardized Precipitation Index (SPI) and the Combined Drought Index (CDI) using rainfall and temperature values and Normalized Difference Vegetation Index values for the period 1980–2010. The results of the two indices show significant correlation. However, CDI is preferred in the analysis of the drought compared to the SPI as it gives drought in more detail, showing extreme, severe, moderate and mild. The study recommends the use of the two methods independently since they give similar results and further recommends trial in other parts of the country affected by drought.

     

植被状况指数的改进及在西北干旱监测中的应用

干旱是全球分布最广、发生频率最高、持续时间最长、影响范围最大、造成的经济损失最为严重的一种自然灾害，干旱也是所有自然灾害中影响因子最为复杂、人类了解最少、监测最为困难的一种自然灾害，干旱监测是世界性的难题。干旱可以发生在任何气候带上，但干旱、半干旱地区是全球干旱灾害发生最频繁的地区。干旱发生特征和规律因地区的不同会有很大的差异，不同地区对干旱监测方法不同。目前，世界各国干旱监测主要利用基于气象、水文、农业和卫星遥感等观测资料建立的各种干旱指数开展，已经有150多种干旱指数。植被状况指数VCI是应用最为广泛的一种卫星监测干旱的指数，研究和业务应用结果表明，VCI对全球各地的干旱均有较好的反映，已经应用在美国国家大气海洋局（NOAA）日常干旱监测业务中，中国国家卫星气象中心干旱卫星遥感监测服务产品也是以VCI为基础。 我国干旱半干旱地区主要分布在新疆、甘肃、青海、陕西、宁夏以及内蒙古自治区的中西部，这里降水少且不稳定，降水变率大，是中国干旱发生频率最高的地区。干旱严重制约着当地经济发展和人类生活质量的提高，使本身非常脆弱的生态环境趋于恶化。为了了解条件植被指数VCI对西北地区不同气候区干旱的监测能力，以上述6省（区）为研究区，利用1982—2003年22年NDVI数据，计算了研究区域22年来逐月的VCI，对比分析了不同气候区VCI与降水距平的关系。结果表明，VCI在空间和时间上较好地反映了西北大部分气候干旱发生、发展和空间分布，是干旱监测的较好指标，但在干旱和极端干旱地区，VCI经常出现异常偏高现象，不能反映干旱气候区常年干旱的基本特点。通过对西北不同生态系统之间NDVI特点和各生态系统间NDVI年变化及其年际变化规律的研究，设计了VCI改进方案，提出了改进的条件植被指数RVCI。通过对22年来逐月RVCI与VCI的对比，RVCI客观地反映了干旱气候区常年干旱特点，较VCI有显著改进。      

Evaluation of drought and wetness episodes in a cold region (Northeast China) since 1898 with different drought indices

Drought identification and drought severity characterization are crucial to understand water scarcity processes. Evolution of drought and wetness episodes in the upper Nen River (UNR) basin have been analyzed for the period of 1951–2012 using meteorological drought indices and for the period of 1898–2010 using hydrological drought indices. There were three meteorological indices: one based on precipitation [the Standardized Precipitation Index (SPI)] and the other two based on water balance with different formulations of potential evapotranspiration (PET) in the Standardized Precipitation Evapotranspiration Index (SPEI). Moreover, two hydrological indices, the Standardized Runoff Index and Standardized Streamflow Index, were also applied in the UNR basin. Based on the meteorological indices, the results showed that the main dry period of 1965–1980 and wet periods of 1951–1964 and 1981–2002 affected this cold region. It was also found that most areas of the UNR basin experienced near normal condition during the period of 1951–2012. As a whole, the UNR basin mainly had the drought episodes in the decades of 1910, 1920, 1970 and 2000 based on hydrological indices. Also, the severity of droughts decreased from the periods of 1898–1950 to 1951–2010, while the severity of floods increased oppositely during the same periods. A correlation analysis showed that hydrological system needs a time lag of one or more months to respond to meteorological conditions in this cold region. It was also found that although precipitation had a major role in explaining temporal variability of drought, the influence of PET was not negligible. However, the sole temperature driver of PET had an opposite effect in the UNR basin (i.e., misestimating the drought detection) and was inferior to the SPI, which suggests that the PET in the SPEI should be determined by using underlying physical principles. This finding is an important implication for the drought research in future.     

Correlation analysis between drought indices and terrestrial water storage from 2002 to 2015 in China

Drought monitoring is a key topic in environmental monitoring and assessment although there is still a need to determine the correlation between drought monitoring indices and remote sensing products. We analyzed the correlation between the self-calibrating Palmer Drought Severity Index (sc_PDSI), the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index (SPEI) and terrestrial water storage monitored through the Gravity Recovery and Climate Experiment (GRACE) on a monthly timescale from 2002 to 2015 in China. As a consequence of anomalies in the soil water budget, the highly significant correlation between the sc_PDSI and the GRACE satellite-observed terrestrial water storage suggested that these two datasets are the most suitable for use in monitoring droughts. In comparing the three drought indices, the sc_PDSI was introduced as a means of drought monitoring in the Yangtze, Pearl, Huaihe, Southeast and Songhua River Basins, whereas the SPEI was found to be more applicable to other major river basins, such as the Inland River Basin. These diverse spatial behaviors are caused by the differences between the hydrological droughts characterized by these three drought indices.     

塔里木河流域干湿变化与大气环流关系

基于塔里木河流域39个气象站1961—2010年逐日观测数据和NCEP/NCAR再分析数据,采用标准化降水蒸散指数（Standardized Precipitation Evapotranspiration Index,SPEI）,分析了该流域近50年来干湿时空变化特征及典型干湿月份和突变前后的大气环流特征。对SPEI序列进行的趋势检验和突变分析表明,近50年来,塔里木河流域显著变湿并在1986年发生显著突变,SPEI上升趋势显著的站点较多的月份主要集中在暖季（5~10月）。对突变前后不同等级干湿事件频率变化的统计结果表明,突变后,极端干旱事件发生频率略有增加,但轻度和中度干旱事件发生频率有所减少,而不同等级的湿事件发生频率则一致地表现为增加。对典型干湿月份和突变前后对应的北半球500hPa位势高度场和风场变化的合成分析表明,暖季典型干湿月份环流系统配置存在明显差异,增加的水汽和弱不稳定大气层结构是该区域1986年后暖季变湿的原因之一。     

黄淮海流域旱涝时空分布及组合特性

以黄淮海流域及其周边地区204个气象站点1961-2010年逐日降水过程资料、国家1:25万DEM数据和1:20万土地利用数据为基础,在利用降水Z指数对黄淮海流域旱涝进行评价的基础上,采用下垫面数据对结果进行修正,并分析黄淮海流域旱涝面积的时间变化特征,对黄淮海地区的易旱区、易涝区进行了划分,进一步选取集对分析法划分了流域内季节间旱涝交替的易发区。结果表明:黄淮海流域内夏秋两季旱涝问题较为严重,且秋旱面积上升趋势较为明显;黄河和海河流域以干旱居多,淮河则是干旱和雨涝并存,季节间的旱涝交替多集中在淮河流域中上游地区。     

植被状态指数VCI与几种气象干旱指数的对比——以河南省为例

使用1982-2006年GIMMS AVHRR NDVI数据集与同期的CI、K、Pa、SPI、Z、PDSI等干旱指数做了对比分析, 讨论了河南省植被状态指数VCI对气象干旱的滞后效应及干旱监测能力. 结果表明: VCI指数与气象干旱指数的相关性受不同下垫面的影响较大, 农地的VCI与气象干旱指数相关性要明显高于林地, 农地VCI与气象干旱指数呈现正相关关系. 在河南省不同的作物生长阶段, VCI对气象干旱有着不同的滞后效应, 其中, 3-5月份冬小麦生长期VCI对气象条件的反应滞后1~3个月, 7、9月份夏玉米生长期VCI对气象条件的反应滞后1月. 总体上看, 结合前期的气象数据, VCI对河南省气象干旱有一定的指示作用和监测能力.     

Application of meteorological and vegetation indices for evaluation of drought impact: a case study for Rajasthan, India

Drought is a serious climatic condition that affects nearly all climatic zones worldwide, with semi-arid regions being especially susceptible to drought conditions because of their low annual precipitation and sensitivity to climate changes. Drought indices such as the standardized precipitation index (SPI) using meteorological data and vegetation indices from satellite data were developed for quantifying drought conditions. Remote sensing of semi-arid vegetation can provide vegetation indices which can be used to link drought conditions when correlated with various meteorological data based drought indices. The present study was carried out for drought monitoring for three districts namely Bhilwara, Kota and Udaipur of Rajasthan state in India using SPI, normalized difference vegetation index (NDVI), water supply vegetation index (WSVI) and vegetation condition index (VCI) derived from the Advanced Very High resolution Radiometer (AVHRR). The SPI was computed at different time scales of 1, 2, 3, 6, 9 and 12 months using monthly rainfall data. The NDVI and WSVI were correlated to the SPI and it was observed that for the three stations, the correlation coefficient was high for different time scales. Bhilwara district having the best correlation for the 9-month time scale shows late response while Kota district having the best correlation for 1-month shows fast response. On the basis of the SPI analysis, it was found that the area was worst affected by drought in the year 2002. This was validated on the basis of NDVI, WSVI and VCI. The study clearly shows that integrated analysis of ground measured data and satellite data has a great potential in drought monitoring.     

An analysis of the drought in Yunnan, China, from a perspective of society drought severity

Drought disaster management entails not only understanding meteorological drought as a natural hazard but also evaluating the adverse societal impacts related to the economy and human lives. For the purpose of quantifying the drought severity from the perspective of society drought, a drought index, namely “Society Drought Severity Index” (SDSI), was put forward to analyze the drought in Yunnan Province of China. In SDSI for Yunnan, the drought severity was represented by the weighted discrepancy between the “appropriate” water needs and the total available water resources, inspired by the established Palmer Drought Severity Index (PDSI). Technically, the trend in historical water consumption records in agricultural, industrial, and domestic sectors was applied to represent the appropriate water needs; an apparent “runoff” was used to represent the available water resource in Yunnan. The SDSI of Yunnan revealed a trend toward increasing drought severity, which resulted from a combination of meteorological changes and water needs escalation. Moreover, the spatial center of the 2010 drought in Yunnan based on SDSI was different from that identified by PDSI, which exactly reflected the influence of water needs on drought severity. The SDSI was deemed to be a beneficial tool for drought disaster management and drought risk governance.     

Drought Monitoring Using Data Mining Techniques: A Case Study for Nebraska, USA

Drought has an impact on many aspects of society. To help decision makers reduce the impacts of drought, it is important to improve our understanding of the characteristics and relationships of atmospheric and oceanic parameters that cause drought. In this study, the use of data mining techniques is introduced to find associations between drought and several oceanic and climatic indices that could help users in making knowledgeable decisions about drought responses before the drought actually occurs. Data mining techniques enable users to search for hidden patterns and find association rules for target data sets such as drought episodes. These techniques have been used for commercial applications, medical research, and telecommunications, but not for drought. In this study, two time-series data mining algorithms are used in Nebraska to illustrate the identification of the relationships between oceanic parameters and drought indices. The algorithms provide flexibility in time-series analyses and identify drought episodes separate from normal and wet conditions, and find relationships between drought and oceanic indices in a manner different from the traditional statistical associations. The drought episodes were determined based on the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI). Associations were observed between drought episodes and oceanic and atmospheric indices that include the Southern Oscillation Index (SOI), the Multivariate ENSO Index (MEI), the Pacific/North American (PNA) index, the North Atlantic Oscillation (NAO) Index, and the Pacific Decadal Oscillation (PDO) Index. The experimental results showed that among these indices, the SOI, MEI, and PDO have relatively stronger relationships with drought episodes over selected stations in Nebraska. Moreover, the study suggests that data mining techniques can help us to monitor drought using oceanic indices as a precursor of drought.     

长江流域陆地水储量与多源水文数据对比分析

从趋势性、滞后性及相关性三方面,对2002—2013年间GRACE重力卫星反演的长江上游与中游陆地水储量与模型模拟土壤含水量、实测降水和实测径流数据进行了对比分析,并从干旱强度及发展时间两方面评估了标准化陆地水储量指数SWSI、标准化降水指数SPI、标准化径流指数SRI和标准化土壤含水量指数SSMI对区域性干旱的表征能力.结果表明:长江上游地区陆地水储量与降水、径流和土壤水蓄量均无显著变化,而中游地区陆地水储量则与水库蓄量同样具有显著性增加,反映人类活动对中游地区陆地水储量变化有很大影响;各指标指示的各等级干旱月份数量基本相当,但各指标反映的特旱具体月份有较大差别,基于GRACE数据构建的SWSI指标对特大干旱的指示性不好;对比各指标对上游与中游地区干旱事件发展时间,体现出水文干旱、农业干旱对气象干旱存在一定的迟滞关系.     

Factors triggering landslide occurrence on the Zemun loess plateau,Belgrade area,Serbia

Among the numerous factors that trigger landslide events, the anthropogenic impact caused by inadequate planning and faulty land use in urban areas is increasing. The Zemun settlement on the northern outskirts of Belgrade has experienced a number of landslides in the last three decades, endangering buildings and roads, and claiming human lives, particularly in the case of the 2010/2011 landslides. Selected meteorological parameters were used to calculate rainfall erosivity indices such as Precipitation Concentration Index and Modified Fournier Index over the period 1991–2015. Drought indices, Lang aridity index and Palfai Drought Index were calculated as well. Mann–Kendall trend test was applied to identify potential rising and/or declining trends both in meteorological parameters and calculated indices. Trend analysis of the annual and seasonal scales yielded a statistically significant trend in the spring time series. Stable arid and pronounced drought conditions were recorded. The modified Fournier index based on monthly mean values yields moderate aggressiveness, with several extreme values indicating very high erosivity classes, especially for 2010/2011. The geological substrate is predominantly loess and hence highly susceptible to erosion and slope failure when climatological conditions are suitable. Accelerated urbanization at the end of the last century reduced vegetation cover, intensified pressure on the vertical loess slope, and lacked suitable rain drainage systems so that surface-water runoff was directed into the porous loess, thereby endangering slope stability. We proposed a geomorphic model to describe the nature of the erosional processes on the loess cliffs of the Zemun loess plateau. Results from this study have implications for mitigation strategies.     

Palmer干旱指数在淮河流域的修正及应用

Palmer指数是目前研究区域干旱时应用最广泛的指数之一,但由于其空间适用性比较强,所以在应用已修正的Palmer指数描述淮河流域干旱等级和持续时间时和实际情况有较大差异,因此有必要做进一步订正。利用淮河流域开封、信阳、巢湖站1961—2009年逐日降水和气温等常规观测资料,根据1965年Palmer指数原理,在200...     

Analyzing drought history using Fuzzy Integrated Drought Index (FIDI): a case study in the Neyshabour basin,Iran

In arid to semi-arid climates, monitoring drought is very complicated because of different hydrometeorology variables effect on it. It is proposed in this paper to develop Fuzzy Integrated Drought Index (FIDI) which combines most important effective factors in developing drought. At first, Variable Infiltration Capacity (VIC) model calibrated simulated runoff to outlet basin runoff data for years 1993–1995. Results represent high performance of model in simulating runoff of outlet basin. Then, Precipitation Anomaly Percentage Index (PAPI), actual Evapotranspiration Anomaly Percentage Index (EAPI), Runoff Anomaly Percentage Index (RAPI), and Soil Moisture Anomaly Percentage Index (SMAPI) were constructed. FIDI was compared with the PAPI, RAPI and SMAPI for the period of 1985 to 2014. The results indicate that (1) the FIDI has more ability in determining start and persistence of drought event compared with PAPI, RAPI, and SMAPI; (2) in the low time scales, PAPI and SMAPI have high correlation with FIDI, and in the higher time scales, RAPI has the high correlation with FIDI; (3) spatially, the middle, west, and portion of north have higher drought risk in the Neyshabour basin.     

Evaluation of CHIRPS and its application for drought monitoring over the Haihe River Basin,China

To establish the drought index objectively and reasonably and evaluate the hydrological drought accurately, firstly, the optimal distribution was selected from nine distributions (normal, lognormal, exponential, gamma, general extreme value, inverse Gaussian, logistic, log-logistic and Weibull), then the Optimal Standardized Streamflow Index (OSSI) was calculated based on the optimal distribution, and last, the spatiotemporal evolution of hydrological drought based on the OSSI series was investigated through the monthly streamflow data of seven hydrological stations during the period 1961–2011 in Luanhe River basin, China. Results suggest: (1) the general extreme value and log-logistic distributions performed prominently in fitting the monthly streamflow of Luanhe River basin. (2) The main periods of hydrological drought in Luanhe River basin were 148–169, 75–80, 42–45, 14–19 and 8–9 months. (3) The hydrological drought had an aggravating trend over the past 51 year and with the increase in timescale, the aggravating trend was more serious. (4) The lower the drought grade was, the broader the coverage area. As for the Luanhe River basin, the whole basin suffered the mild and more serious drought, while the severe and more serious drought only cover some areas. (5) With the increase in time step, the frequency distribution of mild droughts across the basin tended to be concentrated, the frequency of extreme droughts in middle and upper reaches tended to increase and the frequency in downstream tends to decrease. This research can provide powerful references for water resources planning and management and drought mitigation.     

基于CI指数的甘肃省黄土高原地区气象干旱的变化趋势分析

基于甘肃省黄土高原区33个气象站1962-2010年气象资料, 利用综合气象干旱指数(CI)对其近50 a的干旱频率和平均持续时间的空间分布、 干旱强度趋势变化和极端干旱事件频次进行了分析, 此基础上应用基于分型理论的R/S方法对干旱强度未来变化趋势进行了预测. 结果表明: 甘肃省黄土高原区干旱发生频率和多年平均持续天数在兰州-靖远一带和庆阳北部属于高值区, 而岷县、 渭源一带属于低值区; 106° E以西"临洮-通渭-天水"一带和庆阳东南部是干旱变幅最大的地方. 20世纪90年代以来, 干旱强度增大的较快, 四季均呈现出干旱强度变大的趋势, 其中春、 秋季干旱强度加剧的趋势明显, 夏季近10 a都处于非常严重的干旱状态, 但未通过0.01的显著性检验; 20世纪60年代至今, 极端干旱事件发生频次快速增多. 四季干旱强度Hurst指数H 均大于0.5, 同时分维数D 均小于1.5, 因此, 未来一段时间干旱强度仍然保持与过去相一致的变化趋势. 研究结果可为相关部门制定相应抗旱对策提供科学依据.     

An Analysis of Spatial and Temporal Dimension of Drought Vulnerability in Turkey Using the Standardized Precipitation Index

Drought has become a recurrent phenomenon in Turkey in the last few decades. Significant drought conditions were observed during years of late 1980s and the trend continued in the late 1990s. The countrys agricultural sector and water resources have been under severe constraints from the recurrent droughts. In this study, spatial and temporal dimensions of meteorological droughts in Turkey have been investigated from vulnerability concept. The Standardized Precipitation Index (SPI) method was used to detail geographical variations in the drought vulnerability based on frequency and severity of drought events at multiple time steps. Critical (threshold) rainfall values were derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. At regional scale, south-eastern and eastern Anatolia are characterized with moderate droughts at shorter time steps, while the occurrence of severe droughts at shorter time steps is observed at non-coastal parts of the country. A similar picture was observed with very severe droughts. The critical (threshold) values exhibited rising numbers during the growing season at 3-month step in the South-eastern Anatolia, which might have significant consequences considering presence of large irrigation projects under-development in the region. In general, rainfall amounts required for non-drought conditions decrease from the coastal parts toward the interiors with increasing time steps.     

SPI-based evaluation of drought events in Xinjiang, China

Daily precipitation data for 1957?C2009 from 53 stations in the Xinjiang, China, are analyzed, based on the Standardized Precipitation Index (SPI) with the aim to investigate spatio-temporal patterns of droughts. The Mann?CKendall trend test is used to detect the trends in the SPI values of monthly drought series, drought severity and drought duration. The frequencies of moderate, severe and extreme droughts are higher in the North Xinjiang, while mild droughts occur more often in the South Xinjiang. A decreasing frequency of droughts in the North Xinjiang is found in winter, but a drying tendency is detected in the western parts of the North Xinjiang during spring, summer and autumn, which may be harmful for agriculture. The South Xinjiang seems to be getting wetter in summer, while the south parts of the South Xinjiang seem to be getting drier in spring. The middle of the East Xinjiang is identified to be in a slightly dry tendency. The drought severity is decreasing and drought duration is getting shorter in the North Xinjiang, while both of them increase in the southern parts of the South Xinjiang. In addition, droughts in the middle parts of the East Xinjiang are intensifying.