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Contribution of Remote Sensing to Drought Early Warning
Abstract
The main goal of global agriculture is to feed 6 billion people, a number likely to double by 2050. Frequent droughts causing food shortages, economic disturbances, famine, and losses of life limit ability to fulfill this goal. NOAA/NESDIS has recently developed a new numerical method of drought detection and impact assessment from NOAA operational environmental satellites. This is the first globally universal technique to deal with such a complex phenomenon as drought. The method was tested and adjusted based on users' response; validated against conventional data in 25 countries, including all major agricultural producers; and accepted as a tool for monitoring grain production potential. Now, drought can be detected 4-6 weeks earlier than before and delineated more accurately, and its impact on grain production can be diagnosed far in advance of harvest, which is the most vital need for global food security and trade.
... Introduction 2000 ; Skees et al., 2001). Cette expérience entrait dans le cadre d'une initiative plus globale de la Banque, visant à explorer la faisabilité d'une assurance contre les intempéries dans quatre pays en développement (Éthiopie, Maroc, Nicaragua et Tunisie). ...
... Sur le plan des infrastructures nationales, l'Institut National de la Recherche Agronomique (INRA), la Direction de la Stratégie et des Statistiques (DSS- MAPM) et la Direction de la Météorologie Nationale (DMN) ont élaboré en commun le système national de suivi de la campagne agricole et de prévision des rendements céréaliers appelé CGMS-MAROC (www.cgms-maroc.ma). Au niveau des données, la percée significative est venue de l'utilisation des images satellitaires qui a permis d'avoir une estimation des conditions de croissance de la végétation, de façon continue dans l'espace, à des intervalles réguliers et avec une bonne résolution spatiale sur toute la superficie du pays (Kogan, 2000 ; Maselli et al., 2000 ; Balaghi et al., 2008 ; Balaghi et al., 2013). ...
Le présent travail s’inscrit dans le cadre du Projet « Adaptation au Changement Climatique de l’Agriculture du Maghreb » (ACCAGRIMAG), financé par le Fonds Français pour l’Environnement Mondial (FFEM) qui est représenté par l’Agence Française de Développement (AFD).
Le projet vise à :
• Améliorer et diffuser les connaissances sur les impacts du changement climatique en agriculture afin, de renforcer les capacités des acteurs agricoles (petits exploitants, Organisations Professionnelles, services techniques, agro-industriels, assureurs, etc.) à évaluer les risques et intégrer des mesures d’adaptation dans leurs stratégies et leurs pratiques ;
• Accroître les capacités de résilience des systèmes de cultures pluviales, par l’expérimentation et la diffusion de technologies innovantes d’adaptation au changement climatique ;
• Définir des modèles de gestion efficace du risque de sécheresse, par le produit d’assurance dans un contexte de changement climatique.
Le projet cible en premier lieu l’agriculture pluviale à forte dominante céréalière, modèle agricole le plus répandu et le plus vulnérable à la variabilité et au changement climatique. Il s’intéresse en priorité aux communautés paysannes particulièrement sensibles aux aléas et disposant des capacités d’adaptation les moins développées et s’attache ainsi à soutenir la petite et moyenne exploitation agricole.
Le projet ACCAGRIMAG se décline en 3 Composantes opérationnelles et 1 Composante d’assistance technique :
1. Composante 1 : Amélioration et diffusion des connaissances sur les impacts du changement climatique en agriculture et les mesures d’adaptation à mettre en œuvre. Il s’agira d’améliorer la connaissance des risques liés au changement climatique et d’en favoriser l’anticipation en diffusant des outils et des compétences à destination des opérateurs de terrain et de l’assurance, dans les 3 régions d’intervention du Programme d’Appui au Pilier II du Plan Maroc Vert (PAPMV) financé par l’AFD (Fès-Boulemane, Tanger-Tétouan, Taza-Al Hoceima-Taounate).
2. Composante 2 : Expérimentation et diffusion de technologies innovantes. Il s’agira d’accroitre les capacités de résilience des systèmes de cultures pluviales, par l’expérimentation et la diffusion de technologies innovantes d’adaptation au changement climatique. Il s’agira également de diffuser les pratiques agricoles existantes, permettant de conserver et d’améliorer la productivité des sols dans un contexte d’aridification croissante du climat, par l’expérimentation en milieu paysan. Plusieurs types de technologies d’agriculture de conservation pourront être testés par les petits et moyens agriculteurs.
3. Composante 3 : Définition de modèles de gestion efficace des risques climatiques. Il s’agira de tester au Maroc la faisabilité d’une assurance du risque de sécheresse, à partir d’une méthode indicielle qui viendrait en complément ou en substitution de l’assurance « Multirisque Climatique », pour les céréales et légumineuses, qui a été mise place en 2011 dans le cadre d’un Partenariat Public Privé. Le développement des outils d’analyse, de suivi et de pilotage du risque par la télédétection spatiale constitue l’axe central et innovant de cette composante. Le projet étudiera par ailleurs les modalités permettant de rendre l’assurance incitative pour l’adoption de pratiques climato-résilientes d’une part et d’autre part d’expliciter l’impact de l’adoption des pratiques sur l’exposition au risque, donc sur la viabilité financière du système assurantiel dans un contexte de risques hydro-climatiques croissants.
4. Composante 4 (assistance technique): Coordination, pilotage et suivi-évaluation des trois premières Composantes. Il s’agira des actions transversales nécessaires à la bonne exécution du projet.
Le présent travail fait partie de la Composante 3 du projet ACCAGRIMAG. Il s’agit du premier livrable de cette Composante, et il consiste à décrire le dispositif d'acquisition des données nécessaires au fonctionnement du système national de prévision des rendements céréalier, appelé CGMS-MAROC, qui sera utilisé pour tester la faisabilité d’une assurance paramétrique au Maroc pour les céréales.
... Extreme events such as droughts have essential characteristics: intensity, frequency, severity, duration, and spatial coverage, varying among countries and regions. Drought recognises no borders or economic or political differences [93]. Droughts are context-specific hazards categorised into meteorological, hydrological, agricultural, and socio-economic. ...
Early warning systems (EWS) facilitate societies’ preparedness and effective response capabilities to climate risks. Climate risks embody hazards, exposure, and vulnerability associated with a particular geographical area. Building an effective EWS requires consideration of the factors above to help people with coping mechanisms. The objective of this paper is to propose an approach that can enhance EWSs and ensure an effective climate risk resilience development. The paper focuses on the Southern African Development Community (SADC) region and highlights the issues with EWS, identifying weaknesses and characteristics of EWS to help in climate risk adaptation strategies. The SADC region was chosen as the context because it is a climate variability and change hotspot with many vulnerable populations residing in rural communities. Trending themes on building climate risk resilience were uncovered through scientific mapping and network analysis of published articles from 2008 to 2022. This paper contributes to on-going research on building climate risks resilience through early warning systems to identify hidden trends and emerging technologies from articles in order to enhance the operationalization and design of EWS. This review provides insight into technological interventions for assessing climate risks to build preparedness and resilience. From the review analysis, it is determined that there exists a plethora of evidence to support the argument that involving communities in the co-designing of EWS would improve risk knowledge, anticipation, and preparedness. Additionally, Fourth Industrial Revolution (4IR) technologies provide effective tools to address existing EWS’ weaknesses, such as lack of real-time data collection and automation. However, 4IR technology is still at a nascent stage in EWS applications in Africa. Furthermore, policy across societies, institutions, and technology industries ought to be coordinated and integrated to develop a strategy toward implementing climate resilient-based EWS to facilitate the operations of disaster risk managers. The Social, Institutional, and Technology model can potentially increase communities’ resilience; therefore, it is recommended to develop EWS.
... Remotely sensed reflectance has been used to estimate soil and vegetation water content for various crops and to monitor water irrigation per surface unit (Ben-Gal et al., 2010;Ceccato, Flasse, & Grégoire, 2002;Cheng et al., 2012;Hadria et al., 2010;Penuelas, Pinol, Ogaya, & Filella, 1997;Tian, Tong, Pu, Guo, & Zhao, 2001;Trombetti, Riaño, Rubio, Cheng, & Ustin, 2008), drawing on the high temporal and spatial resolution of satellite images. Several indices based on wavelengths ranging between 400 and 2,500 nm have been developed to describe land-surface moisture conditions (Kogan, 2000). Estimation of surface water content values from remote sensing data is usually based on reflectance in the red (R; 610-680 nm), Near Infrared (NIR; 780-890 nm) and Shortwave Infrared (SWIR; 1,580-1,750 nm) regions of the spectrum (Lobell, Asner, Ortiz-Monasterio, & Benning, 2003;Moreno et al., 2014;Muller & Décamps, 2000;Skidmore, Dickerson, & Shimmelpfennig, 1975). ...
Chapter 8
Support irrigation water management of cereals using optical remote sensing and modeling in a semi-arid region
Tarik BENABDELOUAHAB, Hayat Lionboui, rachid hadria, Riad Balaghi, Abdelghani Boudhar, Bernard Tychon
Irrigated agriculture is an important strategic sector for Morocco, contributing to food security and employment. Nowadays, irrigation scheme managers shall ensure that water is optimally used. The main objective was to support the irrigation monitoring and management of wheat in the irrigated perimeter using optical remote sensing and crop modeling. The potential of spectral indices derived from SPOT-5 images was explored for quantifying and mapping surface water content changes at large scale. Indices were computed using the reflectance in red, near infrared and shortwave infrared bands. A field crop-model (AquaCrop) was adjusted and tested to simulate the grain yield and the temporal evolution of soil moisture status. This research aimed at providing a scientific and technical approach to assist policy makers and stakeholders to improve monitoring irrigation and mitigating wheat water stress at field and irrigation perimeter levels in semi-arid areas. The approach could lead to operational management tools for an efficient irrigation at field and regional levels.
... Sur le plan des infrastructures nationales, l'Institut National de la Recherche Agronomique (INRA), la Direction de la Stratégie et des Statistiques (DSS) et la Direction de la Météorologie Nationale (DMN) ont élaboré en commun le système national de suivi de la campagne agricole et de prévision des rendements céréaliers appelé CGMS-MAROC (www.cgms-maroc.ma). Au niveau des données, la percée significative est venue de l'utilisation des images satellitaires qui a permis d'avoir une estimation des conditions de croissance de la végétation, de façon continue dans l'espace, à des intervalles réguliers et avec une bonne résolution spatiale sur toute la superficie du pays (Kogan, 2000 ; Maselli et al., 2000 ; Balaghi et al., 2008 ; Balaghi et al., 2013).Balaghi et al., 2008). ...
Le présent travail s’inscrit dans le cadre du Projet « Adaptation au Changement Climatique de l’Agriculture du Maghreb » (ACCAGRIMAG), financé par le Fonds Français pour l’Environnement Mondial (FFEM) qui est représenté par l’Agence Française de Développement (AFD).
Le projet vise à :
• Améliorer et diffuser les connaissances sur les impacts du changement climatique en agriculture afin, de renforcer les capacités des acteurs agricoles (petits exploitants, Organisations Professionnelles, services techniques, agro-industriels, assureurs, etc.) à évaluer les risques et intégrer des mesures d’adaptation dans leurs stratégies et leurs pratiques ;
• Accroître les capacités de résilience des systèmes de cultures pluviales, par l’expérimentation et la diffusion de technologies innovantes d’adaptation au changement climatique ;
• Définir des modèles de gestion efficace du risque de sécheresse, par le produit d’assurance dans un contexte de changement climatique.
Le projet cible en premier lieu l’agriculture pluviale à forte dominante céréalière, modèle agricole le plus répandu et le plus vulnérable à la variabilité et au changement climatique. Il s’intéresse en priorité aux communautés paysannes particulièrement sensibles aux aléas et disposant des capacités d’adaptation les moins développées et s’attache ainsi à soutenir la petite et moyenne exploitation agricole.
Le projet ACCAGRIMAG se décline en 3 Composantes opérationnelles et 1 Composante d’assistance technique :
1. Composante 1 : Amélioration et diffusion des connaissances sur les impacts du changement climatique en agriculture et les mesures d’adaptation à mettre en œuvre. Il s’agira d’améliorer la connaissance des risques liés au changement climatique et d’en favoriser l’anticipation en diffusant des outils et des compétences à destination des opérateurs de terrain et de l’assurance, dans les 3 régions d’intervention du Programme d’Appui au Pilier II du Plan Maroc Vert (PAPMV) financé par l’AFD (Fès-Boulemane, Tanger-Tétouan, Taza-Al Hoceima-Taounate).
2. Composante 2 : Expérimentation et diffusion de technologies innovantes. Il s’agira d’accroitre les capacités de résilience des systèmes de cultures pluviales, par l’expérimentation et la diffusion de technologies innovantes d’adaptation au changement climatique. Il s’agira également de diffuser les pratiques agricoles existantes, permettant de conserver et d’améliorer la productivité des sols dans un contexte d’aridification croissante du climat, par l’expérimentation en milieu paysan. Plusieurs types de technologies d’agriculture de conservation pourront être testés par les petits et moyens agriculteurs.
3. Composante 3 : Définition de modèles de gestion efficace des risques climatiques. Il s’agira de tester au Maroc la faisabilité d’une assurance du risque de sécheresse, à partir d’une méthode indicielle qui viendrait en complément ou en substitution de l’assurance « Multirisque Climatique », pour les céréales et légumineuses, qui a été mise place en 2011 dans le cadre d’un Partenariat Public Privé. Le développement des outils d’analyse, de suivi et de pilotage du risque par la télédétection spatiale constitue l’axe central et innovant de cette composante. Le projet étudiera par ailleurs les modalités permettant de rendre l’assurance incitative pour l’adoption de pratiques climato-résilientes d’une part et d’autre part d’expliciter l’impact de l’adoption des pratiques sur l’exposition au risque, donc sur la viabilité financière du système assurantiel dans un contexte de risques hydro-climatiques croissants.
4. Composante 4 (assistance technique) : Coordination, pilotage et suivi-évaluation des trois premières Composantes. Il s’agira des actions transversales nécessaires à la bonne exécution du projet.
Le présent travail fait partie de la Composante 3 du projet ACCAGRIMAG. Il s’agit du livrable 3 de cette Composante, et il consiste à décrire la méthodologie de prévision des rendements des trois principales céréales (blé dur, blé tendre et orge) au Maroc, au moyen du système CGMS-MAROC.
Ce travail a été réalisé par les auteurs suivants : Riad BALAGHI (INRA, chef d’équipe) et Mouanis LAHLOU (IAV), Tarik EL HAIRECH (DMN) et Redouane ARRACH (DSS).
... The advent of satellite era has introduced an entirely new technology of satellite remote sensing and a whole range of its application for the benefit of mankind. The use of remotely sensed data from satellite platforms for drought assessment has recently become wide spread (Alemayehu 1999; Amare 2007; Beyene 2007; Chopra 2006; Kogan 2000; Murali et al. 2008; Nageswara et al. 2005; Obi Reddy et al. 2013; Thenkabail et al. 2004; Wani et al. 2010). The use of satellite data using advanced techniques such as remote sensing and Geographic Information System (GIS) can assist in the detection and mapping of agricultural drought prone areas. ...
In dryland semiarid areas of Ethiopia, including large part of East Shewa zone, agricultural drought is common, and farmers inhabiting the area experiences extreme temporal and spatial variability of rainfall in cropping seasons with frequent and longer dry spells. Therefore, spatiotemporal variation of agricultural drought patterns and severity was assessed using Water Requirement Satisfaction Index (WRSI), Standard Precipitation Index (SPI) and Normalized Difference Vegetation Index (NDVI) anomaly. The results indicate that 2000 to 2005 cropping seasons experienced enhanced agricultural drought and reduction of grain yield with spatial difference in severity level. The year 2002 was the most severe of all followed by 2000. Regarding strength of the indices, WRSI, SPI and NDVI anomaly express 76%, 64% and 54% of variability of the grain yield, respectively. Thus, WRSI can be a good indicator for occurrence of agricultural drought. The obtained agricultural risk map indicates that East Shewa zone can be classified into slight, moderate and severe agricultural drought risk zones covering 17.18%, 41.32% and 41.50% of the total area, respectively. Hence, agricultural drought risk mapping can be used to guide decision making processes in drought monitoring, and to reduce the risk of drought on agricultural productivity.
Keywords: Agriculture, Drought, GIS, NDVI, Remote sensing, SPI, WRSI
... Lack of rain is often associated with negative climatic factors such as high temperature, high wind, and low humidity; aggravating the severity of drought. The global statistics of FAO as quoted by Kogan (2000) Svoboda (2000) reported that the annual U. S. A. losses attributable to droughts are in the $ 6 to 8 billion range. No operational EWSs for desertification exist, but monitoring systems could be connected with the operational drought EWSs (Sinange, 1999). ...
Land degradation has been recognized as a global phenomenon affecting the dryland regions of the five continents. The driving forces are variations in climatic conditions and human pressure, and the end products are eroded or salinized unproductive soils. The tragic events of the Dust Bowl of the U.S.A. and the devastating drought of the African Sahel are cited examples. The United Nations Convention to Combat Desertification (CCD) was formulated in 1994 to prescribe relevant measures in the local, national, and regional levels. A Committee on Science and Technology (CST) was established to elaborate the scientific aspects of the convention. The CST began its deliberations in 1997 and has dealt with many issues. First, appropriate indicators were considered to assess institutional trends, and evaluate the impact of undertaken measures to conserve and/or rehabilitate soils. Second, traditional knowledge (TKs) as related to soil and water management was considered, and also possibilities of integrating them with modern technology. Third, early warning systems were considered to establish connection between meteorological, hydrological, and soil moisture droughts. Management of water resources and upgrading the institutional capacity for contingency response planning are pertinent issues. Fourth, possible synergy in the implementation of the three Rio conventions was considered. The pretext is that productive soils offer larger sink to sequester CO 2 , and are conducive to greater biodiversity. The CCD may be considered as both a challenge and a reward to the soil science community. It poses a challenge as the need for innovative interdisciplinary research is becoming too evident. It is a reward as it serves to familiarize soil scientists with the fact that soils are being...
This paper aims to analyze agronomic drought in a highly anthropogenic, semiarid region, the western Mediterranean region. The proposed study is based on Moderate-Resolution Imaging Spectroradiometer (MODIS) and Advanced SCATterometer (ASCAT) satellite data describing the dynamics of vegetation cover and soil water content through the Normalized Difference Vegetation Index (NDVI) and Soil Water Index (SWI). Two drought indices were analyzed: the Vegetation Anomaly Index (VAI) and the Moisture Anomaly Index (MAI). The dynamics of the VAI were analyzed as a function of land cover deduced from the Copernicus land cover map. The effect of land cover and anthropogenic agricultural activities such as irrigation on the estimation of the drought index VAI was analyzed. The VAI dynamics were very similar for the shrub and forest classes. The contribution of vegetation cover (VAI) was combined with the effect of soil water content (MAI) through a new drought index called the global drought index (GDI) to conduct a global analysis of drought conditions. The implementation of this combination on different test areas in the study region is discussed.
Irrigated agriculture is an important strategic sector for Morocco, contributing to food security and employment. Nowadays, irrigation scheme managers shall ensure that water is optimally used. The main objective was to support the irrigation monitoring and management of wheat in the irrigated perimeter using optical remote sensing and crop modeling. The potential of spectral indices derived from SPOT-5 images was explored for quantifying and mapping surface water content changes at large scale. Indices were computed using the reflectance in red, near infrared, and shortwave infrared bands. A field crop model (AquaCrop) was adjusted and tested to simulate the grain yield and the temporal evolution of soil moisture status. This research aimed at providing a scientific and technical approach to assist policymakers and stakeholders to improve monitoring irrigation and mitigating wheat water stress at field and irrigation perimeter levels in semi-arid areas. The approach could lead to operational management tools for an efficient irrigation at field and regional levels.
Located in the mid-west of Morocco, the Tensift watershed shelters the Takerkoust dam, which provides a part of the water used for irrigation of the N'fis agricultural area, which is an important irrigated area of the Tensift watershed. This study deals with the impact of droughts on water inflows to the Takerkoust dam and how the water shortage caused by droughts affects agricultural production in the N'Fis area. The standardized precipitation index (SPI) was used to illustrate the temporal evolution of drought periods. The trend observed on data showed that the Tensift watershed experienced a succession of droughts and humid periods of varying intensities. Periods of droughts have negatively affected water inflows to the Takerkoust dam, and therefore the amount of water allocated to agricultural irrigation. Years that experienced droughts showed a restriction of more than 50% of water volume planned for irrigation. During periods of water scarcity, farmers reduce or completely avoid irrigation of annual crops to save water for irrigation of perennial crops. The water shortage for irrigation has led in some cases to a drop of up to 100% of the surface allocated to the production of annual crops.
How to measure and quantitatively assess hydrological drought (HD) in the inland river basins of Northwest China is a difficult problem because of the complicated geographical environment and climatic processes. To address this problem, we conducted a comprehensive approach and selected the Aksu River Basin (ARB) as a typical inland river basin to quantitatively assess the hydrological drought based on the observed data and reanalysis data during the period of 1980–2010. We used two mutual complementing indicators, i.e., the standardized runoff index (SRI) and standardized terrestrial water storage index (SWSI), to quantitatively measure the spatio-temporal pattern of HD, where the SRI calculated from the observed runoff data indicate the time trend of HD of the whole basin, while SWSI extracted from the reanalysis data indicate the spatial pattern of HD. We also used the auto-regressive distribution lag model (ARDL) to show the autocorrelation of HD and its dependence on precipitation, potential evapotranspiration (PET), and soil moisture. The main conclusions are as follows: (a) the western and eastern regions of the ARB were prone to drought, whereas the frequency of drought in the middle of the ARB is relatively lower; (b) HD presents significant autocorrelation with two months’ lag, and soil moisture is correlated with SWSI with two months’ lag, whereas PET and precipitation are correlated with SWSI with 1 month’ lag; (c) the thresholds of HD for annual PET, annual precipitation, and annual average soil moisture are greater than 844.05 mm, less than 134.52 mm, and less than 411.07 kg/m², respectively. A drought early warning system that is based on the thresholds was designed.
Soil moisture is one of the critical parameters in climatic, ecological and hydrological modeling and vegetation growth. Soil moisture is important for environmental studies but due to ground-based point measurement of soil moisture is expensive and impractical for watershed measurement, this parameter is not be used widely to simulate and predict models. Overall and uniform view on different part of land, repetitive photography from wide and inaccessible areas along with data with regular periods and decrement effects of plans on environment are important criteria's of remote sensing. Rangeland growth is heavily functioning of the water availability therefore the vegetation index from satellites may respond to the change of soil moisture. We used MODIS sensor images with the consideration of economical aspects, availability of images and high radiometric, temporal and spatial resolution to estimate the surface soil moisture. MODIS images were provided by Iranian Space Agency for the day's availability of soil moisture field data matched by satellite images. Radiometric and geometric correction was conducted by orbital parameters on all images and the images were converted to BIL format and shifted in relation to accurate boundary of Caspian sea. Using bathymetry map of Caspian Sea, atmospheric correction was conducted by dark pixel method. This case study analyzes the correlation the surface soil moisture measured gravimetric sampling and MODIS NDVI (250m by 250m), compares the collected coincided and lagged soil moisture and MODIS NDVI. Also estimates the soil moisture using NDVI by linear regression models during growing season (April-Aug) from 2003 through 2005 in arid and semi arid rangeland in Khorasan Razavi Province. NDVI shows lag to soil moisture because of vegetations response lag it. Results show that surface soil moisture in arid and semi arid rangelands has moderate correlation with simultaneous and lagged NDVI and can be estimated using NDVI during growing season. Stronger relations can be obtained with surface soil moisture data that are lagged by 2 weeks with respect to the vegetation index.
The high plateaus of Algeria is a critical region to policymakers in terms of social, economic, and infrastructure development. The main goal of the present work was to monitor the climatic drought and its impact on vegetation health across the Algerian high plateaus using remote sensing techniques. Vegetation health index (VHI) showed a clear drought in the western region of the study area. The results show practically three periods of drought were evident: October to December 2006, November to December 2009, and December 2012. Agreeable correlations among the obtained results using standard precipitation index for 3 months (SPI-3) and other satellite indicators such as temperature vegetation dryness index (TVDI) and VHI were obtained. TVDI and VHI agreed well with the ground-based observations from SPI-3; thus, these may serve as key and easily accessible indicators of drought. The research shows motivating results that decision makers can use to take timely corrective measures to minimize the reduction in agricultural production in drought prone areas. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).
Various remote sensing-based drought indices have been developed during the past decades. These indices have their own applicability. Examination of adaption associated with limitations in drought indices would be useful for index selection and improvement. In this study, five drought indices (e.g. the temperature condition index (TCI), vegetation condition index (VCI), vegetation health index (VHI), temperature vegetation dryness index (TVDI), drought severity index (DSI)) generated by time series of MODIS data, which include 8-day MOD11 LST products, MOD13 NDVI products and MOD16 ET/PET products at 1km resolution from 2000 to 2012, were performed in Henan, and Shaanxi province in the northern China, aiming to better understand the differences and potential monitoring ability among these drought indices. 8-day drought indices were compared against winter wheat yield at the prefecture-city scale from 2000 to 2012. Results showed that TVDI outperformed the five drought indices in correlation with winter wheat yield, and followed by DSI, and next is the VHI, whereas TCI and VCI have the lowest correlation. Furthermore, during the winter wheat growth period, drought shows varying agricultural impacts on winter wheat yield at different phenological stages, jointing-heading stage and flowering-filling stage have higher correlations than others, and the highest correlation coefficient can reach 0.8, which indicated that winter wheat requires more water during these stages. As a result, the sensitive phenological stages can be used as the key period for effective agricultural drought monitoring. And during the two highest correlation growth period — jointing-heading stage and flowering-filling stage, higher correlations were found between TVDI and the winter wheat yield, which the correlation coefficient can reach 0.5. Furthermore, the correlation between drought indices and yield in Shaanxi province is generally stronger than that of Henan province, which showed that remote sensing drought indices have a better indication in rain fed area on drought.
Remote sensing data and models for drought monitoring and early warnings must be validated and calibrated before they become operational to specific region and hydro-climatic conditions. The main objective of this research was to evaluate vegetation indices for agricultural drought monitoring. In order to achieve the objective of the study, a relationship between a 3 month Standardized Precipitation Index (SPI) and the respective growing season vegetation indices were first modeled using ordinary least square to vegetation conditions respond to rainfall variability. The coefficient of determination indicates the relationship was highest with Drought Severity Index (DSI) (R2=0.85) while it was lowest with VCI (R2=0.53). Relationships between four known MODIS vegetation indices products (NDVI, DSI, VCI an Eta) and crop yield were examined to compare the performances of vegetation indices for drought detection and monitoring. DSI was found to be the best to define agricultural drought phenomena among the four indices (R2=0.76). DSI is followed by VCI, NDVI and Eta. DSI was an efficient and reliable drought index among the four indices analysed. Consequently, drought vulnerable areas were identified and characterized. The results indicate that the study area can be classified into no stress, low stress and high stress agricultural drought risk sub-zones covering 34.94%, 43.18% and 21.88% of the total area, respectively. The present findings, would help to fill the gap by contributing evidences of effectiveness of vegetation indices in monitoring agricultural drought.
Key Words: Drought monitoring, Growing season, Remote sensing, SPI, Vegetation indices
Extreme events can cause severe damage in several sectors such as agriculture, forests and fisheries. In order to facilitate early detection of these harmful episodes, adequate climate and agrometeorological databases must be ensured. Some observational data and products necessary for early detection are presented in this paper. It briefly reviews the main features of proper databases that provide quality controlled data and products, useful to the end-users, easily accessible and in a timely manner. The data can be accessed through the standardization of database management and electronic accessibility. The main features and importance of data collection, automatic weather stations (AWS), database management and relational database management systems (RDBMS) are described. Examples of agrometeorological databases, database management systems and their applications and accessibility are given. Remote sensing (geostationary satellites, NOAA-Advanced Very High Resolution Radiometer (AVHRR), radar and lighting detectors) offers a valuable source of spatial information and can be complementary or even alternative to ground-based observations. Due to the processing of data from various sources in agrometeorology, and the need to display them in maps, geographical information systems (GIS) are in wider use today. GIS can help to identify the risk, extent and severity of many extreme events. Some examples of applications of remote sensing and GIS are presented. Finally, training, interdisciplinary collaboration and communication between users and developers of products are referred as essential means to achieve these goals.
Irrigated agriculture is an important strategic sector in arid and semi-arid regions. Given the large spatial coverage of irrigated areas, operational tools based on satellite remote sensing can contribute to their optimal management. The aim of this study was to evaluate the potential of two spectral indices, calculated from SPOT-5 high-resolution visible (HRV) data, to retrieve the surface water content values (from bare soil to completely covered soil) over wheat fields and detect irrigation supplies in an irrigated area. These indices are the normalized difference water index (NDWI) and the moisture stress index (MSI), covering the main growth stages of wheat. These indices were compared to corresponding in situ measurements of soil moisture and vegetation water content in 30 wheat fields in an irrigated area of Morocco, during the 2012–2013 and 2013–2014 cropping seasons. NDWI and MSI were highly correlated with in situ measurements at both the beginning of the growing season (sowing) and at full vegetation cover (grain filling). From sowing to grain filling, the best correlation (R2 = 0.86; p < 0.01) was found for the relationship between NDWI values and observed soil moisture values. These results were validated using a k-fold cross-validation methodology; they indicated that NDWI can be used to estimate and map surface water content changes at the main crop growth stages (from sowing to grain filling). NDWI is an operative index for monitoring irrigation, such as detecting irrigation supplies and mitigating wheat water stress at field and regional levels in semi-arid areas.
Drought indices (DI) are an useful tool for assessing different sectarian droughts. Standardized Precipitation Index (SPI) has been used worldwide to assess/monitor the onset, active phase, cessation and severity of drought. Normalized Difference Vegetation Index (NDVI) provides a comprehensive vegetation dynamics, which directly linked with rainfall received in a particular region. Indo-Gangetic Region (IGR), providing employment and livelihood to tens of millions of rural families directly or indirectly and rice (Oryza sativa L.)–wheat (Triticum aestivum L.) (RW) system of the Indo-Gangetic Plains (IGP) contributes 80% of the total cereal production and is critical to food security of the region. This study tries to verify the applicability of water-vegetative indices viz., SPI, Rainfall Index (RI) and NDVI for drought assessment of rice–wheat system productivity over IGR-India. The relationship between monsoon rainfall and NDVI shows that at around 1100mm rainfall, the NDVI reached saturation point and no further significant increase in NDVI with increase of rainfall is noticed. Even though, there was a positive correlation of seasonal monsoon rainfall and average NDVI, conflicting results are noticed between monthly distribution of rainfall and monthly anomaly of NDVI over IGR States. It is noticed that June dif NDVI (actual NDVI–mean NDVI) contributes more to rice productivity followed by July. However, the combined effect of June, July and August, explains 15% of the variation of Kharif Rice Productivity Index (KRPI). As far as wheat is concerned, statistically significant relation was found between Wheat Productivity Index (WPI) and anomaly NDVI during December–March. This explains 35% of the variability in WPI.
In Morocco, no operational system actually exists for the early prediction of the grain yields of wheat (Triticum aestivum L.). This study proposes empirical ordinary least squares regression models to forecast the yields at provincial and national levels. The predictions were based on dekadal (10-daily) NDVI/AVHRR, dekadal rainfall sums and average monthly air temperatures. The Global Land Cover raster map (GLC2000) was used to select only the NDVI pixels that are related to agricultural land. Provincial wheat yields were assessed with errors varying from 80 to 762kgha−1, depending on the province. At national level, wheat yield was predicted at the third dekad of April with 73kgha−1 error, using NDVI and rainfall. However, earlier forecasts are possible, starting from the second dekad of March with 84kgha−1 error, at least 1 month before harvest. At the provincial and national levels, most of the yield variation was accounted for by NDVI. The proposed models can be used in an operational context to early forecast wheat yields in Morocco.
The historical region of Fertile Crescent (FC) was recently hit by an intense and prolonged drought episode during the two hydrological years spanning between 2007 and 2009. Here, we characterize the temporal and spatial extents of this extreme drought at the monthly and seasonal scales and perform a first assessment on the associated impact in the hydro-meteorological fields, as well as the consequent influence on vegetation dynamics and cereal productions.This episode corresponds to the driest two-year case for the FC area since 1940, although just slightly drier than the 1998–2000 drought. Precipitation decline was mostly noticeable over Iraq (up to 70%), with the suppression of rainfall particularly acute during the first hydrological year (2007–2008). From the meteorological perspective, winter and transition months were dominated by high pressures that inhibited synoptic activity entering from the eastern Mediterranean and favoured relative north-easterly winds and drier air masses with low convective instability.The impact of the 2007–2009 drought in vegetation was evaluated with Normalized Difference Vegetation Index (NDVI) obtained from VEGETATION instrument. It is shown that large sectors of south-eastern Turkey, eastern Syria, northern Iraq and western Iran present up to six months of persistently stressed vegetation (negative NDVI anomalies) between January and June 2008. During the following dry year (2008–2009) dry areas are restricted to northern Iraq with up to five months of stressed vegetation. Finally we looked at the impacts on cereal production (wheat and barley) in the region and it is shown that the major grain-growing countries in the area (Syria, Iraq and Iran) were significantly affected by this drought, particularly in the year 2008.
Geospatial techniques have played a key role in studying different types of hazards either natural or manmade. Temporal satellite data of three years 2000, 2005 and 2010 are used to monitor and assess the drought severity and the impact of agricultural drought on crop production. In Bankura District, agricultural drought and crop failure have been common and spatial variability of rainfall in cropping season with frequent and longer dry spells. This makes them vulnerable to the risk of agricultural drought. This study is conducting with the objective of assessing agricultural drought risk and it's impacts on yield reduction using RS and GIS techniques. The digital indices using satellite data namely, NDVI (Normalized difference Vegetation index) and NDVI anomaly can be prepared from the long term mean values of maximum NDVI to assess the severity of drought. VCI(Vegetation condition Index), TCI(Temperature condition Index), SPI(Standardized Precipitation Index), MSI(Moisture Stress Index) and YVI(Yellowness vegetation Index) is very essential to Assess the agricultural drought. The impact of agricultural drought on crop production was measured through estimation of yield reduction(in %). Compared to other cropping seasons of the analysis period, yield reduction for the year 2005 was lesser than the highly drought years 2000 and 2010. Simple regression analyses has performed between Land surface temperature with NDVI, TCI with VCI and SPI,MSI, NDVI Anomaly, VCI with Yield reduction(%). Finally, a resultant drought vulnerability map was obtained by integrating NDVI Anomaly, MSI, SPI, VCI, TCI and YVI which indicates the area facing a combined drought. The combined vulnerability map shows that 6% area has no risk, 53 % area face moderate risk and 41 % area face high risk within the entire geographical area. Thus, this agricultural drought risk mapping can be useful to guide decision making process in drought monitoring and to reduce the risk of drought on agricultural production and productivity.
Agricultural and Forest Meteorology j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t a b s t r a c t The historical region of Fertile Crescent (FC) was recently hit by an intense and prolonged drought episode during the two hydrological years spanning between 2007 and 2009. Here, we characterize the temporal and spatial extents of this extreme drought at the monthly and seasonal scales and perform a first assess-ment on the associated impact in the hydro-meteorological fields, as well as the consequent influence on vegetation dynamics and cereal productions. This episode corresponds to the driest two-year case for the FC area since 1940, although just slightly drier than the 1998–2000 drought. Precipitation decline was mostly noticeable over Iraq (up to 70%), with the suppression of rainfall particularly acute during the first hydrological year (2007–2008). From the meteorological perspective, winter and transition months were dominated by high pressures that inhibited synoptic activity entering from the eastern Mediterranean and favoured relative north-easterly winds and drier air masses with low convective instability. The impact of the 2007–2009 drought in vegetation was evaluated with Normalized Difference Vegeta-tion Index (NDVI) obtained from VEGETATION instrument. It is shown that large sectors of south-eastern Turkey, eastern Syria, northern Iraq and western Iran present up to six months of persistently stressed vegetation (negative NDVI anomalies) between January and June 2008. During the following dry year (2008–2009) dry areas are restricted to northern Iraq with up to five months of stressed vegetation. Finally we looked at the impacts on cereal production (wheat and barley) in the region and it is shown that the major grain-growing countries in the area (Syria, Iraq and Iran) were significantly affected by this drought, particularly in the year 2008.
Remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS), a climatic water budget model, and the STATSGO database were used within a GIS environment to determine the influences of hydrologic soil properties on soil moisture and thermal emission in western–central Kansas for a dry year, 2000. Two important variables, water-holding capacity (WHC) and hydrologic soil group (HSG), were controlled in our water budget experiment to evaluate their impacts on soil moisture content (SMC) changes throughout the period. Results showed that HSG affected drought detection and occurrence very little, but WHC variations explained most local variations of soil moisture content. As a strong indicator of relative soil moisture deficit, the Standardized Thermal Index (STI) patterns were also influenced by WHC. Generally, the earlier the soil moisture content drops below 40%, the earlier the STI reaches a threshold value of 0.2 or higher. Vegetation responses to thermal detection lagged behind the STI by up to 8 weeks, which was computed by comparing the STI and Normalized Difference Vegetation Index (NDVI) deviation from a 10-year mean. The spatial pattern of lag-times was not apparent, but lag-times were correlated with a WHC component.
Agriculture is defined as “the production and processing of plant and animal life for the use of human beings” and also “a system for harvesting or exploiting the solar radiation.” Meteorology is “the science of atmosphere.” “The study of those aspects of meteorology, which have direct relevance to agriculture,” is defined as agricultural meteorology for which the abbreviated form is “Agrometeorology” (Murthy 1996). The primary aim of agricultural meteorology is to extend and fully utilize the knowledge of atmospheric and other related processes to optimize sustainable agricultural production with maximum use of weather resources and with little or no damage to the environment. This science also provides the necessary information to help reduce the negative impact of risks and uncertainties of adverse weather through agrometeorological services (Motha et al. 2006). According to Murthy and Stigter (2003), agrometeorological services are “all agrometeorological and climatological information that can be directly applied to improve or protect agricultural production (yield quality, quantity, and income obtained from yields) while protecting the agricultural production base from degradation.” Sivakumar et al. (2004) observed that the current status of agricultural production and increasing concerns with related environmental issues call for improved agrometeorological services for enhancing and sustaining agricultural productivity and food security around the world.
"Droughts are recurring climatic events, which often hit South Asia, bringing significant water shortages, economic losses and adverse social consequences. Preparedness for drought should form an important part of national environmental policies. At present, countries of the region have limited institutional and technical capacity to prepare for a drought and to mitigate its impacts. Information on drought onset and development is not readily available to responsible agencies and to the general public. This report describes the first results of the development of the near-realtime drought-monitoring and reporting system for the region, which includes Afghanistan, Pakistan and western parts of India. The system is being developed using drought-related characteristics (indices), which are derived from remote-sensing data. The indices include a deviation from the normalized difference vegetation index (NDVI) from its long-term mean and a vegetation condition index (VCI). "The study first investigated the historical pattern of droughts in the region using monthly time-step AVHRR satellite data for 1982-1999. Droughts in recent years were studied using 8-day time-interval MODIS satellite images available from year 2000 onwards. The unique feature of the study is the development of regression relationships between drought-related indices obtained from MODIS and AVHRR data, which have different pixel-resolution and optical characteristics. These relationships were established for each month of the year separately, as well as for the pooled data of all months, and explained up to 95 percent of variability. The relationships were validated in randomly chosen districts outside the study area. The results ensure the continuity of the two data sets and will allow the reports on drought development in the region to be made in near-real time with a spatial resolution of 500 meters and at 8-day intervals. A continuous stream of MODIS data is available free of charge, on the Internet, from the USGS EROS data centre. The operational mode for the MODIS-AVHRR-based droughtreporting system is currently being developed. The goal is to make the system available, via Internet, to all stakeholders in the region, including government agencies, research institutions, NGOs and the global research community. It may be used as a drought-monitoring tool and as a tool for decision support in regional drought assessment and management."
Remote sensed information on vegetation and soil moisture, namely the Normalised Difference Vegetation Index (NDVI) and the Soil Water Index (SWI), is employed to monitor the spatial extent, severity and persistence of drought episodes over Continental Portugal, from 1999 to 2006. The severity of a given drought episode is assessed by evaluating the cumulative impact over time of drought conditions on vegetation. Special attention is given to the drought episodes that have occurred in the last decade, i.e., 1999, 2002 and particularly the major event of 2005. During both the 1999 and 2005 drought episodes negative anomalies of NDVI are observed over large sectors of Southern Portugal for up to nine months (out of eleven) of the vegetative cycle. On the contrary, the 2002 event was characterized by negative anomalies in the northern half of Portugal and for a shorter period (eight out of eleven months). The impact of soil moisture on vegetation dynamics is evaluated by analyzing monthly anomalies of SWI and by studying the annual cycle of SWI vs. NDVI. While in the case of the drought episode of 1999 the scarcity of water in the soil persisted until spring, in the recent episode of 2005 the deficit in greenness was already apparent at the end of summer. The impact of dry periods on vegetation is clearly observed in both arable land and forest, and it is found that arable land presents a higher sensitivity. From an operational point of view, obtained results reveal the possibility of using the developed methodology to monitor, in quasi real-time, vegetation stress and droughts in Mediterranean ecosystems.
The IR channels of the AVHRR are calibrated in-flight with data acquired when the AVHRR views space and a warm target on board. This determines the two coefficients of a linear calibration equation. However, in its 11- and 12-micron channels the response of the AVHRR is nonlinear. If not accounted for, the nonlinearity could cause errors as large as 2 C in inferred scene temperatures. Therefore NESDIS computes corrections to the brightness temperatures inferred from the linear calibration. This paper describes how the corrections have been calculated at NESDIS since March 1986 and presents the corrections for the AVHRRs on the NOAA 9, 10, and 11 satellites. The corrections are calculated from results of the prelaunch calibration.
Developing a national or provincial drought policy and plan is a complicated but essential first step toward a reduction of societal vulnerability. Until recently, nations had devoted little effort toward drought planning, preferring instead the crisis management approach. Presently, an increasing number of nations are pursuing a more proactive approach that emphasizes the principles of risk management and sustainable development. Because of the multitude of impacts associated with drought and the numerous governmental agen-cies that have responsibility for some aspect of monitoring, assessment, mitigation, and planning, developing a policy and plan must be an integrated process within and between levels of government. This chapter outlines in considerable detail a generic process that can be adopted by governments that desire to develop a more comprehensive approach to drought management.
This paper assesses the major impacts on human lives and the economy of the United States resulting from weather events attributed to El Niño 1997-98. Southern states and California were plagued by storms, whereas the northern half of the nation experienced much above normal cold season temperatures and below normal precipitation and snowfall. Losses included 189 lives, many due to tornadoes, and the major economic losses were property and crop damages from storms, loss of business by the recreation industry and by snow removal equipment/supplies manufacturers and sales firms, and government relief costs. Benefits included an estimated saving of 850 lives because of the lack of bad winter weather. Areas of major economic benefits (primarily in the nation's northern sections) included major reductions in expenditures (and costs) for natural gas and heating oil, record seasonal sales of retail products and homes, lack of spring flood damages, record construction levels, and savings in highway-based and airline transportation. Further, the nation experienced no losses from major Atlantic hurricanes. The net economic effect was surprisingly positive and less government relief was needed than in prior winters without El Niño influences. The estimated direct losses nationally were about 19 billion The highly accurate long-range predictions issued by the Climate Prediction Center in the summer of 1997 for the winter conditions led to some major benefits. For example, the predictions led California to conduct major mitigation efforts and the results suggest these led to a major reduction in losses. Several utilities in the northern United States used the winter forecasts to alter their strategy for purchasing natural gas, leading to major savings to their customers.
Drought is one of the major environmental disasters in southern Africa. In recent years, the damage from droughts to the environment and economies of some countries was extensive, and the death toll of livestock and wildlife was unprecedented. Weather data often come from a very sparse meteorological network, incomplete and/or not always available in good time to enable relatively accurate and timely large scale drought detection and monitoring. Therefore, data obtained from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board the NOAA polar-orbiting satellites have been studied as a tool for drought monitoring and climate impact assessment in southern Africa. The AVHRR-based vegetation condition index (VCI) and temperature condition index (TCI) developed recently were used in this study because in other parts of the globe they showed good results when used for drought detection and tracking, monitoring excessive soil wetness, assessment of weather impacts on vegetation, and evaluation of vegetation health and productivity. The results clearly show that temporal and spatial characteristics of drought in southern Africa can be detected, tracked, and mapped by the VCI and TCI indices. These results were numerically validated by in situ data such as precipitation, atmospheric anomaly fields, and agricultural crop yield. In the later case, it was found that usable corn yield scenarios can be constructed from the VCI and TCI at approximately 6 (in some regions up to 13) weeks prior to harvest time. These indices can be especially beneficial when used together with ground data.
Records of top-of-the-atmosphere albedo over several sites around the globe indicate that the formulae given in Rao and Chen (1996) to determine the post-launch calibration of the visible (channel 1, 0.58-0.68 mu m) and near-infrared (channel 2, 0.72-1.1 mu m) channels of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-14 spacecraft overestimate the in-orbit degradation of the two channels, resulting in spurious upward trends in the albedo time series. Therefore, the calibration formulae have been revised to minimize the upward trends, utilizing a 3-year (1995-1997) record of albedo measurements over a calibration site (21-23 N, 28-29 E) in the southeastern Libyan desert. Formulae for the calculation of the revised calibration coefficients as a function of elapsed time in orbit are given. The revised calibration formulae presented here, and those presented in Rao and Chen (1996), yield radiance/albedo values within 5% (relative) of each other for about 900 days after launch in channel 1 and for about 500 days in channel 2.
Drought is one of the most adverse and powerful weather-related disasters that occur every year across a portion of the United States. The consequences of droughts quite often can be devastating. To mitigate these consequences, droughts require careful monitoring. Recently, NOAA's National Environmental Satellite Data and Information Service developed a new Advanced Very High Resolution Radiometer-based vegetation condition index (VCI) that showed good results when it was used for drought detection and tracking. The VCI is a vegetation index with reduced noise and is adjusted for land climate, ecology, and weather conditions. This index provides a quantitative estimate of weather impact on vegetation and also measures vegetation conditions. Several large-area experiments showed that the VCI had excellent ability to detect drought and to measure the time of its onset and its intensity, duration, and impact on vegetation. The VCI provides accurate drought information not only for the cases with well-defined, prolonged, widespread, and very strong droughts, but also for very localized, short-term, and ill-defined droughts. The advantages of this index compared to conventional ground data are in providing more comprehensive, timely, and accurate drought information. This paper describes the methodology and technical principles used to derive the vegetation condition index, explores data processing, and gives many examples of VCI application for drought monitoring in the United States during 1985-90. The spatial and temporal patterns of VCI-derived drought were in a very good agreement with the identical patterns identified from precipitation and yield anomalies.
Crop production assessments are extremely valuable because of their economic importance in influencing international trade and national economic policies. This study investigates using the Vegetation Condition Index derived from NOAA/AVHRR satellite data to estimate the maize production for the United States Corn Belt. Satellite data from 1985 to 1992 are utilized within a model and explain more than 50 per cent of the variation in the normalized yields from 42 Crop Reporting Districts. Results estimating the regional maize production are encouraging, and operational estimates using this model would be available for about two months prior to the maize harvest in the Corn Belt.
Drought is the most damaging environmental phenomenon. During 1967-91,
droughts affected 50% of the 2.8 billion people who suffered from
weather-related disasters. Since droughts cover large areas, it is
difficult to monitor them using conventional systems. In recent years
the National Oceanic and Atmospheric Administration has designed a new
Advanced Very High Resolution Radiometer- (AVHRR) based Vegetation
Condition Index (VCI) and Temperature Condition Index (TCI), which have
been useful in detecting and monitoring large area, drought-related
vegetation stress. The VCI was derived from the Normalized Difference
Vegetation Index (NDVI), which is the ratio of the difference between
AVHRR-measured near-infrared and visible reflectance to their sum. The
TCI was derived from the 10.3-11.3-mm AVHRR-measured radiances,
converted to brightness temperature (BT). Algorithms were developed to
reduce the noise and to adjust NDVI and BT for land surface
nonhomogeneity. The VCI and TCI are used to determine the water- and
temperature-related vegetation stress occuring during drought. This
paper provides the principles of these indices, describes data
processing, and gives examples of VCI-TCI applications in different
ecological environments of the world. The results presented here are the
first attempt to use both NDVI and thermal channels on a large area with
very diversified ecological resources. The application of VCI and TCI
are illustrated and validated by in situ measurements. These indices
were also used for assessment of drought impact on regional agricultural
production in South America, Africa, Asia, North America, and Europe.
For this purpose, the average VCI-TCI values for a given region and for
each week of the growing season were calculated and compared with yields
of agricultural crops. The results showed a very strong correlation
between these indices and yield, particularly during the critical
periods of crop growth.
NDVI (Normalized Difference Vegetation Index) images generated from NOAA AVHRR GVI data were recently used to monitor large scale drought patterns and their climatic impact on vegetation. The purpose of this study is to use the Vegetation Condition Index (VCI) to further separate regional NDVI variation from geographical contributions in order to assess regional drought impacts. Weekly NDVI data for the period of July 1985 to June 1992 were used to produce NDVI and VCI images for the South American continent. NDVI data were smoothed with a median filtering technique for each year. Drought areas were delineated with certain threshold values of the NDVI and VCI. Drought patterns delineated by the NDVI and VCI agreed quite well with rainfall anomalies observed from rainfall maps of Brazil. NDVI values reflected the different geographical conditions quite well. Seasonal and interannual comparisons of drought areas delineated by the VCI provided a useful tool to analyse temporal and spatial evolution of regional drought as well as to estimate crop production qualitatively. It is suggested that VCI data besides NDVI may be used to construct a large scale crop yield prediction model.
Editor's note: This article is based on a presentation to the Symposium on theInternational Decade for Natural Disaster Reduction, 24 January 1994 in Nashville,Tennessee. The symposium was held in conjunction with the AMS Annual Meeting.
The post-launch degradation of the visible (channel 1: 0.58- 068 microns) and near-infrared (channel 2: approx. 0.72 - l.l microns) channels of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-7, -9, and -11 Polar-orbiting Operational Environmental Satellites (POES) was estimated using the south-eastern part of the Libyan Desert as a radiometrically stable calibration target. The relative annual degradation rates, in per cent, for the two channels are, respectively: 3.6 and 4.3 (NOAA-7); 5.9 and 3.5 (NOAA-9); and 1.2 and 2.0 (NOAA-11). Using the relative degradation rates thus determined, in conjunction with absolute calibrations based on congruent path aircraft/satellite radiance measurements over White Sands, New Mexico (USA), the variation in time of the absolute gain or slope of the AVHRR on NOAA-9 was evaluated. Inter-satellite calibration linkages were established, using the AVHRR on NOAA-9 as a normalization standard. Formulae for the calculation of calibrated radiances and albedos (AVHRR usage), based on these interlinkages, are given for the three AVHRRs.
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