Annual Standardized Precipitation Index Research Articles

Spatial and temporal characteristics of drought in the Mu Us Sandy Land based on the Standardized Precipitation Index

The environment of the Mu Us Sandy Land, northern Shaanxi, is fragile, so the temporal and spatial evolution of drought can provide a reference for ecological construction and agricultural production. Based on the daily precipitation data of five meteorological stations from 1967 to 2020, the spatial and temporal evolution characteristics of drought in the Mu Us Sandy Land of northern Shaanxi were analyzed using the methods Standardized Precipitation Index (SPI) and run-length theory. The results show that 1) the smaller the time scale, the higher the sensitivity of the SPI to primary precipitation. 2) The annual, summer, autumn, and winter SPI showed an upward and a wetting trend, and the fastest wetting speed is observed in summer, while spring showed an increasing trend of drought. 3) In the past 54 years, the duration, degree, and intensity of drought events at SPI-3 and SPI-12 scales in the Mu Us Sandy Land of northern Shaanxi showed an insignificant decreasing trend, but the decreasing rate at the SPI-12 scale was faster than that at the SPI-3 scale. The serious periods of drought are November 2018 to May 2019 and April 1999 to July 2021. 4) The duration of drought events at two timescales in each region showed a decreasing trend. The longest durations of drought were in Yulin and Jingbian; Shenmu and Dingbian are the regions with the fastest reduction rate of drought degree at the two scales. Hengshan shows rapid reduction of drought intensity at the two scales and also the region with large average drought intensity. These results are helpful in understanding and describing drought events for drought risk management under the condition of global warming.

Is the Gridded Data Accurate? Evaluation of Precipitation and Historical Wet and Dry Periods from ERA5 Data for Canadian Prairies

Precipitation is crucial for the hydrological cycle and is directly related to many ecological processes. Historically, measurements of precipitation totals were made at weather stations, but spatial and temporal coverage suffered due to the lack of a robust network of weather stations and temporal gaps in observations. Several products have been proposed to identify the location of the occurrence of precipitation and measure its intensity from different types of estimates, based on alternative data sources, that have global (or quasi-global) coverage with long historical time series. However, there are concerns about the accuracy of these estimates. The objective of this study is to evaluate the accuracy of the ERA5 product for two ecoregions of the Canadian Prairies through comparison with monthly means measured from 1981–2019 at ten weather stations (in-situ), as well as to assess the intraseasonal variability of precipitation and identify dry and wet periods based on the annual Standardized Precipitation Index (SPI) derived from ERA5. A significant relationship between in-situ data and ERA5 data (with the R2 varying between 0.42 and 0.76) (p < 0.01)) was observed in nine of the ten weather stations analyzed, with lower RMSE in the Mixed Ecoregion. The Mean Absolute Percentage Error (MAPE) results showed greater agreement between the datasets in May (average R value of 0.84 and an average MAPE value of 32.33%), while greater divergences were observed in February (average R value of 0.57 and an average MAPE value of 50.40%). The analysis of wet and dry periods, based on the SPI derived from ERA5, and the comparison with events associated with the El Niño-Southern Oscillation (ENSO), showed that from the ERA5 data and the derivation of the SPI it is possible to identify anomalies in temporal series with consistent patterns that can be associated with historical events that have been highlighted in the literature. Therefore, our results show that ERA5 data has potential to be an alternative for estimating precipitation in regions with few in-situ stations or with gaps in the time series in the Canadian Prairies, especially at the beginning of the growing season.

Drought monitoring by downscaling GRACE-derived terrestrial water storage anomalies: A deep learning approach

The current study proposes a new method to downscale the monthly GRACE-derived Terrestrial Water Storage Anomaly (TWSA) to 10 km spatial resolution over Iran using deep learning methods. First, the growing neural gas (GNG) method is utilized to cluster the TWSA data to find similar patterns. The Silhouette Chou Davies (SCD) validity measure, a combination of three robust cluster validity measures, is used to evaluate the performance of the GNG method. Then, the feasibility of deep learning Convolutional Long Short-Term Memory (ConvLSTM), shallow learning Feed Forward Neural Networks (FFNN), and Random Forest (RF) are examined in downscaling GRACE-derived TWSA using only remote sensing images. The results indicate that the deep learning method outperforms the RF and FFNN models by 7 % and 18 %, respectively. Then, the Ground Water Storage (GWS) data are isolated from TWSA, showing an agreement between the GRACE-derived GWS and ground-based measurements with R2 = 0.76. Additionally, the downscaled TWSA is used to generate annual drought frequency and change detection maps for the GWS from 2002 to 2016. Annual standardized precipitation index (SPI) drought frequency maps are also produced to gain deeper insight into the water resource scarcity of Iran. The results indicate that Iran has experienced water resource overexploitation since 2011 for agricultural activities, while meteorological drought is a trigger and intensifier for the water crisis in Iran. According to the results, Iran experienced exceptional drought in some regions, and the GWS has decreased all over the country. In addition, further analysis of Iran’s water resources is provided until 2022. The current study calls for integrated sustainable water resources management in Iran; otherwise, irreversible water and environmental problems with higher frequencies will be expected in the near future.

Assessing and mapping human well-being for sustainable development amid drought and flood hazards: Dadu River Basin of China.

Drought and flood are two of the most destructive natural disasters with the most significant impact and greatest losses in the Dadu River basin (DRB). However, their impacts on people's life have not attracted enough attention from scholars. In this study, the Standardized Precipitation Index (SPI) describing the drought/flood situation and the Composite Index of Human Well-being (CIHW) are calculated, and a framework is further constructed to assess the impacts of drought and flood disasters on human well-being in the DRB. The results show that the annual and seasonal SPI in the DRB generally exhibit an increasing trend in fluctuations during 2000-2009, indicating a wetting climate in this basin. Overall, the upper reaches of the DRB have experienced an evolution of flood-drought-flood state transition, where the variation amplitude of the SPI in the western sub-basin is greater than that in the eastern sub-basin. In addition, the lower reaches of the DRB have suffered more dramatic and periodic changes from the drought/flood disasters in terms of the SPI. For human well-being during 2000-2019, Maerkang City in the upper reaches, Kangding City in the middle reaches, and Shimian County in the lower reaches of the DRB are at a relatively higher level, with the CIHW decreasing from administrative centers to the around. Moreover, the CIHW over the whole basin increases gradually from 2000 to 2019. The SPI has significantly negative effects on different capitals, following a descending order of financial, social, physical, human and natural capitals. The counties of the basin are divided into four groups, namely the group with high disaster risks and high human well-being, the group with high disaster risks and low human well-being, the group with low disaster risks and high human well-being, and the group with low disaster risks and low human well-being. The panel regression results suggest that the construction of water conservancy facilities, the financial inputs in agriculture and meteorology, and the educational level have positive impacts on human well-being, but the impacts differ from different groups. The construction of water conservancy facilities has highly significant impacts on human well-being in all groups; the education level has no significant impact on the group with high disaster risk and high human well-being, which has not passed the significance test; while the financial inputs in agriculture and meteorology have relatively higher impacts on the whole basin and on the group with low disaster risk and low human well-being compared with other groups. Therefore, it is suggested that the negative impacts of drought and flood disasters can be mitigated through strengthening infrastructure construction, responding appropriately to climate change, avoiding disasters at the source of major projects and improving the disaster prevention and mitigation systems.

Drought Analysis in Southern Agroclimatic Zone of Tamil Nadu using Standardized Precipitation Index

Drought differs from other natural hazards in the fact that the initiation and the termination is extremely difficult to determine and that its drastic effects continue to persist well after the cessation of the event which adds to the complexity as well as the casualties. The Southern Agro Climatic Zone (ACZ) of Tamil Nadu is heavily rain shadowed during the South West Monsoon Season, several complications arise with respect to drought, causing crop failures and depleted moisture concentration in certain cases. With that idea in perspective, a study was conducted in Agro Climate Research Centre, Tamil Nadu Agricultural University, Coimbatore, India to study the frequency of drought over the Southern Agro-Climatic Zone of Tamil Nadu, India. Since precipitation that occurs over a region determines mainly the occurrence and cessation of drought events, precipitation-based Rainfall Deviation and Standardized Precipitation Index (SPI) was used to quantify the extent of rainfall deficit or surplus over the region. The analysis of 30 years (1991 – 2020) historical rainfall data of various districts of the Southern Agroclimatic Zone of Tamil Nadu using SPI showed that the annual SPI value ranged from +3.3 to -4. The study showed that Tirunelveli and Thoothukudi districts were most prone to moderate drought and severe drought. The region showed more frequency of Moderate drought than Severe and Extreme drought.

Spatiotemporal Characteristics and Trends of Meteorological Droughts in the Wadi Mina Basin, Northwest Algeria

Drought has become a recurrent phenomenon in Algeria in the last few decades. Significant drought conditions were observed during the late 1980s and late 1990s. The 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 the Wadi Mina basin (4900 km2) were investigated to assess vulnerability. The Standardized Precipitation Index (SPI) method and GIS were used to detail temporal and geographical variations in drought based on monthly records for the period 1970–2010 at 16 rainfall stations located in the Wadi Mina basin. Trends in annual SPI for stations in the basin were analyzed using the Mann–Kendall test and Sen’s slope estimator. Results showed that the SPI was able to detect historical droughts in 1982/83, 1983/84, 1989/90, 1992/93, 1993/94, 1996/97, 1998/99, 1999/00, 2004/05 and 2006/07. Wet years were observed in 1971/72, 1972/73, 1995/96, 2008/09 and 2009/10. Six out of 16 stations had significant decreasing precipitation trends (at 95% confidence), whereas no stations had significant increasing precipitation trends. Based on these findings, measures to ameliorate and mitigate the effects of droughts, especially the dominant intensity types, on the people, community and environment are suggested.

Wet and dry periods in the state of Alagoas (Northeast Brazil) via Standardized Precipitation Index

The state of Alagoas has its economic base directed to agriculture, and the knowledge of wet and dry periods is fundamental for the success of agricultural enterprises. The objective was to define the wet and dry periods in the state of Alagoas via multivariate analysis applied to the Standardized Precipitation Index (SPI). Monthly rainfall data for 20 weather stations from 1960 to 2016 were used, with fault filling via imputation. Moreover, Cluster analysis (CA) was applied to the time series (definition of homogeneous regions) and SPI-12 (annual) - (determination of dry and wet spell periods). The annual accumulated rainfall showed two distinct periods: 1960 to 1990 (P1) and 1990 to 2016 (P2), according to Pettitt test. Both periods alternate according to the phases of La Niña and Neutral (rainy years) and El Niño (dry years). In the monthly rainfall, only the Eastern part of Alagoas increased the rainy months during long time series. In tested connection methods, the average connection, also known as cophenetic correlation coefficient (CCC = 0.8760), represented homogeneous groups of rainfall, featuring two regions: one on the coast (G1) and another hinterland and arid (G2); and two non-homogeneous groups (NA) in the state. The annual SPI helped identify dry and wet periods, regardless of El Niño-Southern Oscillation (ENSO) categorization. The SPI-12 categories show high annual and decadal variability in the groups, except for the extremely dry and wet categories. There is greater variability in dry and wet periods near the coast than hinterland of the state.

An enhanced water storage deficit index (EWSDI) for drought detection using GRACE gravity estimates

Accurate detection and monitoring of drought events are important particularly in arid and semi-arid regions of the world. Gravity Recovery and Climate Experiment (GRACE) gravity estimates have been used widely for this purpose and a number of indices have been developed using the GRACE Terrestrial Water Storage Anomalies (TWSA) values. In the current study, a new approach is proposed to enhance the performance of the GRACE-based Water Storage Deficit Index (WSDI). The proposed Enhanced Water Storage Deficit Index (EWSDI) was developed based on the grid-based standardization of the Water Storage Deficit (WSD) values. The decomposed time series of the TWSA were computed in an attempt to evaluate the performance of the approach based on different components of the TWSA time series. Standardized Precipitation Index (SPI) and modelled Soil Moisture Storage (SMS) were also used to validate the functionality of this new GRACE-derived index. The applicability of the EWSDI index was tested in the semi-arid climatic conditions of Turkey and the results showed that the detrended EWSDI better correlated with SPI-09 and annual SPI with correlation coefficient values of 0.70 and 0.76, respectively. The findings also suggested an approximate enhancement of 13% over the existing WSDI when applied on the detrended TWSA. The findings of this study reveal that the proposed approach is effective in improving the performance of the existing WSDI to detect drought events in terms of monthly and annual correlation coefficients achieved.

Assessment of drought using standard precipitation index in Prakasam district Andhra Pradesh, India

This paper discusses a method for calculating the severity of meteorological droughts based on historical precipitation data as the primary criterion Monthly precipitation data from 1970 to 2020 were used to obtain Standardized Precipitation Index (SPI) values for Prakasam district, Andhra Pradesh. SPI has the ability to analyse the drought at various time scales and for a variety of applications. SPI is calculated at various time scales (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 etc. months). Time scales of one, two, and three months are effective for agriculture, while time scales of six, nine, and twelve months are useful for hydrology. A drought event occurs any time the SPI is continuously negative and reaches an intensity of -1.0 or less. The event ends when the SPI becomes positive. Each drought event, therefore, has a duration defined by its beginning and end, and an intensity for each month that the event continues. The annual SPI for Prakasam district was calculated from 1970 to 2020 to show the frequency of occurrence of dry and wet conditions. Temporal SPI graphs show that the maximum SPI value (extreme drought) occurred in the year 2018 in that year, the SPI value was -2.6. Furthermore, in severe and extreme drought years, SPI values indicated only moderate dryness rather than extreme dryness, with SPI values never falling below -2.5.Severe and moderate drought occurred in 1984, 2002 and 2014. Drought patterns were evaluated, yielding many interesting results on the variability of drought occurrence in the region. The study's findings are relevant to climate change studies in order to understand historical patterns and build future scenarios of drought occurrences.

Variability and Transitions in Precipitation Extremes in the Midwest United States

AbstractMonthly to seasonal precipitation extremes, both flood and drought, are important components of regional climates worldwide, and are the subjects of numerous investigations. However, variability in and transition between precipitation extremes, and associated impacts are the subject of far fewer studies. Recent such events in the Midwest region of the United States, such as the 2011–12 flood to drought transition in the upper Mississippi River basin and the flood to drought transition experienced in parts of Kentucky, Ohio, Indiana, and Illinois in 2019, have sparked concerns of increased variability and rapid transitions between precipitation extremes and compounded economic and environmental impacts. In response to these concerns, this study focuses on characterizing variability and change in Midwest precipitation extremes and transitions between extremes over the last 70 years. Overall we find that the Midwest as a region has gotten wetter over the last seven decades, and that in general the annual maximum and median wetness, defined using the standardized precipitation index (SPI), have increased at a larger magnitude than the annual minimum. We find large areas of the southern Midwest have experienced a significant increase in the annual SPI range and associated magnitude of transition between annual maximum and minimum SPI. We additionally find wet to dry transitions between extremes have largely increased in speed (i.e., less time between extremes), while long-term changes in transition frequency are more regional within the Midwest.

Investigation of spatiotemporal variation of drought in Iran during the last five decades

The present study was conducted to assess the changes in Iran's drought severity for the duration of 1964 to 2014. For this purpose, the spatial distribution of drought was annually and seasonally evaluated using climate data from 26 synoptic stations over Iranian territory based on standardized precipitation index (SPI). In this regard, the climate classification in the study area was performed applying Dermartone method. Moreover, the annual and seasonal values of SPI were calculated for the whole Iranian territory and each climate region. The SPI index for monotonic trend was calculated in each climate region utilizing Mann-Kendall and Theil Sen estimators. Our results implied that the minimum and maximum values of SPI (-3.86 and 2.89, respectively) appeared during spring in dry and Mediterranean climate regions. In addition, the maximum and minimum values of annual continuous SPI appeared in 1999-2004 and 1974-1982, respectively. The maximum and minimum values of seasonal continuous SPI also appeared for a duration of 9 years during summers respectively in the period of 1977 to 1985 and springs in the period of 2006 to 2014. The application of Mann-Kendall and Theil Sen estimator analyses revealed that 9 out of 26 stations had a significant decreasing SPI trend. Moreover, the annual and seasonal time series in moderately dry regions indicated a meaningfully decreasing trend in winter and annual SPI. Additionally, winter, spring, autumn and annual values of SPI had a meaningful decreasing trend in the Mediterranean climate region. In dry and very wet climate regions, no obvious trend was detected for the annual or seasonal SPI index.

Rainfall extremes and drought in Northeast Brazil and its relationship with El Niño–Southern Oscillation

AbstractThe objective of this study was to evaluate the annual standardized precipitation index (SPI) obtained from the DrinC software based on multivariate analysis in the identification of rainfall and drought extremes in the State of Alagoas and its relationship with El Niño–Southern Oscillation. Monthly rainfall data from 1960 to 2016 from National Water Agency were analysed. Annual SPI (SPI‐12) has been designed for comparison with ENSO phases via Oceanic Niño Index for 3.4 region and in identifying climate extremes in the State of Alagoas. The principal component analysis and cluster analysis techniques were applied to the rainfall series of SPI‐12. Extreme events were identified in both rainy and drought periods according to SPI‐12, and were associated with the ENSO phases (El Niño, La Niña, and Neutral). The first four principal components explained 46.68% of the variance. Our findings are crucial for agriculture and civil defence since northeastern Brazil has several areas of risk and social vulnerability.

Meteorological drought analysis using Standardized Precipitation Index over Luni River Basin in Rajasthan, India

The study aimed to monitor the spatial extent and severity of drought events in the Luni River Basin using Standardized Precipitation Index (SPI), and hence, the long-term monthly precipitation records of 39 rain gauge stations (1973–2016) were used in the study. Both the long-term (24, 12, and 9 months) and short-term (6, 3, and 1 month) SPI were calculated to recognize the drought events and the percentage of the area covered by the severe drought conditions. The nonparametric Mann–Kendall test was performed for trend analysis in drought events to investigate the consistency of drought events. The frequency results of drought events revealed that Jalore station was the highest drought frequency station, while the lowest drought frequency was observed in Vijaynagar station. The annual SPI result showed that the following years witnessed major drought events: 1981, 1984, 1985, 1988, 1989, 1991, 1993, 1999, 2000, 2004, 2005, and 2008. Besides, the results of the Mann–Kendall test showed that a substantial portion of the eastern basin experienced an increase in the intensity of drought, while the western basin experienced a decrease in the severity of the drought. The comprehensive analysis is indicative of climate change, and there is a possibility that such droughts would become more common in the future in the Luni River Basin. The results of this study would help planners to develop sound policy on water resources and also assist in forecasting systems to provide advance warnings.

SPEI ve SPI İndisleri Kullanılarak İstanbul-Damlıca Deresi Havzasında Kuraklık Şiddetlerinin Analizi

Drought is the most complex and damaging event in climatic disasters. Precipitation is the most important factor to control agricultural production in arid and semi-arid regions. The problem of drought in some regions in Turkey shows itself especially effect on the ecosystem and agriculture.The aim of this study is to determine the frequency and severity of drought with Standardized Precipitation Evapotranspiration Index (SPEI) and compare with Standardized Precipitation Index (SPI) using meteorological data measured between 1982 and 2006 in Damlica creek basin located in Istanbul-Buyukcekmece drinking water basin. The SPEI drought index estimates evapotranspiration with Thornthwaite equation. In the regression analysis between the 25-year data set and the annual SPEI and SPI indices, the coefficient of determination (R2) between the annual SPI and SPEI drought indices according to the second order polynomial was found to be 0.977 and found to be statistically significant. However, there were differences between drought severities in monthly, seasonal and 6-month drought periods. According to the annual evaluation results; SPEI Index was determined as 4 years of moderate drought (1983, 1989, 2004, 2006), 7 years of mild drought (1982, 1992, 1993, 1994, 1999, 2000, 2003), and SPI index was found as 2 years of severe drought (1983, 1989), 3 years of moderate drought (1982, 2004, 2006) and 2 years of mild drought (1992, 1993). The SPEI drought index calculated by precipitation, temperature and evapotranspiration data may give healthier results to policy makers in drought mitigation policies in terms of giving more accurate results in agricultural production and drought assessments.

Climate-based crop pattern determination using Standard Precipitation Index (SPI) and the Oldeman classification in Sangiran Site

Sangiran Site is dominated by rainfed field. Climate parameters, especially rain intensity affects crop patterns. Farmers strongly depend on rain intensity to support productivity thus they need climate-based crop patterns. Sangiran Site is prone to drought hazard since the region has a limited access to groundwater, which is henced by deep well in the region. Drought becomes the main threat to agriculture within Sangiran. This study aims to analyse meteorological drought and crop pattern determination using the SPI and the Oldeman classification respectively. Rainfall data is derived from multi temporal CHIRPS data. A monthly time series with thirty consecutive years (1988–2017) was used to calculate the annual SPI. The annual SPI help to determine crop patterns which is suitable for the region. The results of the study show that angiran Site has monsoonal rainfall with one peak of dry season, and one peak of wet season. Rainfed field is at the highest risk when drought lasts for above four months. Climate based crop patterns with the Oldeman classification indicate that Sangiran Site is classified into type C2 which is adequate for two times palawija crops and one time paddy crops.

Kırsal Havzalarda Kuraklığın İki Yöntem (SPEI ve SPI) Kullanılarak Belirlenmesi: Kumdere Havzası Örneği

Atmosfer kaynaklı afetlerin içinde kuraklık en karmaşık ve hasar veren bir olaydır. Kurak ve yarı kurak ülkelerin en önemli sorunlarından biri, bitkilerin gelişimi için ihtiyaç duyulan suyun, yağışın miktar ve dağılımının yetersizliği nedeniyle yeterli miktarda ve gerekli zamanda bulunamamasıdır. Bu ülkelerde tarımsal üretim genelde yağışın doğal dağılımına, miktarına ve sulamaya bağlı olarak değişim göstermektedir. Kısacası kurak ve yarı kurak bölgelerde yağış, tarımsal üretimi kontrol eden en önemli faktördür. Türkiye'de de bazı bölgelerde kuraklık sorunu kendini özellikle tarım sektörüne ve ekosisteme yaptığı etkiler ile göstermektedir. Bu çalışmanın amacı Meriç nehir havzasında yer alan Kumdere havzasında 1985-2009 yılları arası havzada ölçülmüş meteorolojik veriler kullanılarak kuraklığın sıklığı ve şiddetinin Standartlaştırılmış Yağış Evapotranspirasyon İndisi (SPEI) ile belirlenmesi ve Standartlaştırılmış Yağış İndisi (SPI) ile karşılaştırılmasıdır. SPEI kuraklık indisi evapotranspirasyonu Thornthwaite eşitliği ile tahmin etmektedir. 25 yıllık veri seti ile yıllık SPEI ve SPI İndeksleri arasındaki regresyon analizinde, ikinci derece polinoma göre yıllık SPI ve SPEI kuraklık indeksleri arasında determinasyon katsayısı (R2) 0.95 olarak belirlenmiş ve istatistiksel olarak anlamlı bulunmuştur. Ancak aylık, mevsimlik ve altı aylık kuraklık değerlendirmelerinde kuraklık şiddetleri arasında farklar görülmüştür. Yıllık değerlendirme sonuçlarına göre; SPEI indisi ile havzada 7 yıl hafif kurak (1985, 1986, 1991, 1993, 2001 2004 ve 2007). 2 yıl orta kurak (2000, 2002), 1 yıl aşırı kurak (2008). SPI indisi ile ise 1 yıl aşırı kurak (2008), 1 yıl orta kurak (2000) ve 8 yıl hafif kurak (1985, 1986, 1991, 1992, 1993, 2001, 2002 ve 2004) yıl olarak tespit edilmiştir. Tarımsal üretim açısından yağış, sıcaklık ve evapotranspirasyon verileri ile hesaplanan SPEI kuraklık indisi kırsal havzalarda bitki gelişme dönemlerinde tarımsal yönden özellikle aylık kuraklık değerlendirmelerinde daha hassas sonuçlar verdiği için kuraklığın azaltılması politikalarında karar vericilere daha sağlıklı sonuçlar verebilir.

Evaluating the utility of various drought indices to monitor meteorological drought in Tropical Dry Forests.

Even though existing remote-sensing-based drought indices are widely used in many different types of ecosystems, their utility has not been widely assessed in tropical dry forests (TDFs). The aim of this study is to evaluate the performance of three remote-sensing-based drought indices, the Vegetation Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI), for meteorological drought monitoring in TDFs using the moderate-resolution imaging spectroradiometer (MODIS) products. The correlation between the VCI, TCI, and VHI and multiple time scales of the Standardized Precipitation Index (SPI) (1, 3, 6, 9, 12, 15, 18, 21, 24months) for each month (January to December) and each season (dry season, dry-to-wet season, wet season and wet-to-dry season) were conducted using the Pearson correlation analysis. We also correlated year-to-year changes of satellite-based drought indices with the changes of the in situ annual SPI (A_SPI) which provides annual information on the mean meteorological drought. The analysis reveals that the ability of these remote-sensing-based drought indices for meteorological drought monitoring varies with timing, and the TCI outperforms the VCI and VHI in terms of seasonal and annual scale. These remote-sensing indices performed well in monitoring meteorological drought in the dry season, poorly in the in the dry-to-wet season, and moderately in the wet season. The TCI performed best in monitoring meteorological drought in the wet-to-dry period, followed by VHI, whereas the VCI performed worst. All of these remote-sensing-based drought indices failed to detect drought in May during the green-up period and in September, October, and November when the water content in the root regions was abundant. Our results indicate that the evapotranspiration of TDFs is more sensitive than canopy greenness to detect meteorological drought. Results from this study increase the ability to provide real-time drought monitoring and early warnings of drought in TDFs.

Drought Analysis of Iğdır Turkey

Climate change increases the odds of worsening drought in many parts of the World. Climate projections for the Mediterranean basin in which Turkey is located expresses alarming conclusions about severe droughts. Droughts are expected to prevail in different severities and periods throughout Turkey. Iğdır plain, which lies in eastern part of Turkey is convenient for cultivation of many agricultural products because of its fertile soils and micro-climatic properties. In this study, drought analysis were carried out for Iğdır by using Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI) and Streamflow Drought Index (SDI). The data (precipitation and flow) were obtained in monthly intervals from Turkish institutions, namely General Directorate of Meteorology and General Directorate of State Hydraulic Works. Study was aimed to examine the integrated effect of low precipitations and high temperatures on hydrological and meteorological drought. Annual SPI results show that four severe and three moderate drought events whereas RDI detected four severe and four moderate drought events for the study period (47 years, 1971-2018). SPI index detected severe category droughts in the water years of 1980, 1989 and 1997. RDI detected severe category droughts in the mentioned years together with one more event in 2000. SDI identified 2002 as extreme drought year, and identified 1982, 1984, 1986 and 2002 as moderate drought years. The output of the study is aimed to serve for better understanding of droughts in the Igdir Plain.

Regional applicability analysis of four drought indices in Chongzuo of South China

Based on the precipitation anomaly percentage index (Pa), the relative moisture index (MI), the standardized precipitation index (SPI), and the standardized precipitation evapotranspiration index (SPEI), the regional applicability was examined in Chongzuo over the period 1961to 2012. The results showed that: (1) The MI and Pa significantly underestimated severe drought and extreme drought at annul time scale. The monitoring result of annual SPEI and SPI was accurate and more close to the actual drought level. (2) The frequency range of different drought class is close to actual level for the SPI and SPEI at different time scale. The severe and extreme drought seldom occurred using Pa and MI monitoring results, the adaptability and reliability of MI were relatively lower in Chongzuo. (3) The annual MI and Pa showed smaller coverage with the severity of moderate and above drought than statistical results of SPI and SPEI in Chongzuo. (4) The SPI was found more sensitive to precipitation changes than the SPEI at 1-month scale in dry period. SPI and SPEI can be properly used for the monitoring as well.

Assessment the effect of drought and land use change on vegetation using Landsat data

Drought is a disaster phenomenon especially in arid and semi-arid areas. Vegetation and its production play a main role in the social and economic issues in every country. In this study, Standardized Precipitation Index (SPI) and Normalized Difference Vegetation Index (NDVI) data have been used to monitor drought and the vegetation condition in Sonqor Abad in, Kermanshah province. Meteorological station data in the study area was used to study the SPI as a drought index. The maps of NDVI and also land use changes were provided using Landsat-TM images for 2001, 2008 and Landsat 8 images for 2015 in ENVI software environment. The obtained results showed that the land uses of cultivation and fallow have decreased and rangeland, urban and rock mass have increased. On the other hand, the dense of rainfall in the vegetation density has increased in this area during 2001 until 2015. Due to population growth and expansion of urban areas, the farm and garden lands have decreased around the city during this period. The correlation was found between vegetation density in mid-spring and the annual SPI of last year. Therefore, it can be concluded that there is a direct relationship between rainfall and the density of vegetation. By increasing the amount of rainfall and SPI, the vegetation density is increased. Based on the results, it is recommended that in addition to using meteorological data, satellite images should be used for monitoring the drought.