Browsing by Author "Thenkabail, Prasad"

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Closing of the Krishna Basin: Irrigation, Streamflow Depletion and Macroscale Hydrology
(2007) Biggs, Trent W.; Gaur, Anju; Scott, Christopher; Thenkabail, Prasad; Gangadhara Rao, Parthasaradhi; Gumma, Murali Krishna; Acharya, Sreedhar; Turral, Hugh
"Discharge from the Krishna River into the ocean decreased by 75 percent from 1960-2005, and was zero during a recent multi-year drought. This paper describes the physical geography and hydrology of the Krishna Basin, including runoff production and a basic water account based on hydronomic zones. More than 50 percent of the basin's irrigated area is groundwater irrigation, which is not currently included in inter-state allocation rules. Future water allocation will require inclusion of the interactions among all irrigated areas, including those irrigated by groundwater and surface water."
Global Croplands and their Importance for Water and Food Security in the Twenty-first Century: Towards an Ever Green Revolution that Combines a Second Green Revolution with a Blue Revolution
(2010) Thenkabail, Prasad
"In an increasingly food insecure world, there is a critical need for us to have a comprehensive understanding of global croplands. The reality that the 'green revolution' has ended is beginning to be felt around the World. Whereas, global population continues to increase at a rate of about 100 million per year and is expected to reach around 10 billion by 2050, cropland areas are not increasing and have stagnated around 1.5 billion hectares globally. Indeed, cropland areas have even begun to decrease in some countries with important food contribution (e.g., USA) due to increasing demand of fertile arable lands for alternative uses such as bio-fuels, encroachment from urbanization, and industrialization."
A Holistic View of Global Croplands and Their Water Use for Ensuring Global Food Security in the 21st Century Through Advanced Remote Sensing and Non-Remote Sensing Approaches
(2010) Thenkabail, Prasad
"This paper presents an exhaustive review of global croplands and their water use, for the end of last millennium, mapped using remote sensing and non-remote sensing approaches by world’s leading researchers on the subject. A comparison at country scale of global cropland area estimated by these studies had a high R2-value of 0.89–0.94. The global cropland area estimates amongst different studies are quite close and range between 1.47–1.53 billion hectares. However, significant uncertainties exist in determining irrigated areas which, globally, consume nearly 80% of all human water use. The estimates show that the total water use by global croplands varies between 6,685 to 7,500 km3 yr−1 and of this around 4,586 km3 yr−1 is by rainfed croplands (green water use) and the rest by irrigated croplands (blue water use). Irrigated areas use about 2,099 km3 yr−1 (1,180 km3 yr−1 of blue water and the rest from rain that falls over irrigated croplands). However, 1.6 to 2.5 times the blue water required by irrigated croplands is actually withdrawn from reservoirs or pumping of ground water, suggesting an irrigation efficiency of only between 40–62 percent. The weaknesses, trends, and future directions to precisely estimate the global croplands are examined. Finally, the paper links global croplands and their water use to a paradigm for ensuring future food security."
An Irrigated Area Map of the World (1999) Derived from Remote Sensing
(2006) Thenkabail, Prasad; Biradar, Chandrashekhar M.; Turral, Hugh; Noojipady, Praveen; Li, Y. J.; Vithanage, J.; Dheeravath, Venkateswarlu; Velpuri, Manohar; Schull, M.; Cai, X. L.; Dutta, R.
"It is necessary to accurately quantify the area and intensity of irrigation in the world in order to properly understand its contribution to food production and security, and to estimate its water use, as competition for water increases with rising urban and industrial needs and the recognition of environmental water requirements. Satellite remote sensing offers a relatively cheap, repeatable and accurate technology to estimate and monitor irrigated areas. This research report presents the results of a global analysis of multi-temporal time series at nominal 10 kilometer pixel resolution. Statistics of irrigation at country level are derived from these maps for different seasons and for the entire year (annualized) for the nominal year of 1999. Three methods of area abstraction are used and compared, and three methods of accuracy assessment are applied. The annualized irrigated areas of the world at the end of the last millennium were about 480 Mha of which there were 263 Mha for season 1, 176 Mha for season 2, and 41 Mha for continuous cropping. Of this, Asia alone accounts for 78 percent (375 Mha) with 59 percent from China and India. The country statistics are compared with FAO country-level statistics (see Annex I). The IWMI GIAM 10 km V2.0 map were tested based on 3 sources of independent data resulting in accuracies between 84 and 91 percent with errors of omission not exceeding 16 percent and errors of commission less than 21 percent. The total area available for irrigation (TAAI; the nearest equivalent to FAO's equipped area)was 412 Mha. The global irrigated area mapping (GIAM) products (e.g., maps, statistics, web maps) are made available through a dedicated web portal (http://www.iwmigiam.org). The detailed methodology is also made available through the web portal. The focus of this research report is on the results of the GIAM mapping effort."
Irrigated Area Maps and Statistics of India Using Remote Sensing and National Statistics
(2009) Thenkabail, Prasad; Dheeravath, Venkateswarlu; Biradar, Chandrashekhar M.; Gangalakunta, Obi Reddy P.; Noojipady, Praveen; Gurappa, Chandrakantha; Velpuri, Manohar; Gumma, Murali Krishna; Li, Yuanjie
"The goal of this research was to compare the remote-sensing derived irrigated areas with census-derived statistics reported in the national system. India, which has nearly 30% of global annualized irrigated areas (AIAs), and is the leading irrigated area country in the World, along with China, was chosen for the study. Irrigated areas were derived for nominal year 2000 using time-series remote sensing at two spatial resolutions: (a) 10-km Advanced Very High Resolution Radiometer (AVHRR) and (b) 500-m Moderate Resolution Imaging Spectroradiometer (MODIS). These areas were compared with the Indian National Statistical Data on irrigated areas reported by the: (a) Directorate of Economics and Statistics (DES) of the Ministry of Agriculture (MOA), and (b) Ministry of Water Resources (MoWR). A state-by-state comparison of remote sensing derived irrigated areas when compared with MoWR derived irrigation potential utilized (IPU), an equivalent of AIA, provided a high degree of correlation with R2 values of: (a) 0.79 with 10-km, and (b) 0.85 with MODIS 500-m. However, the remote sensing derived irrigated area estimates for India were consistently higher than the irrigated areas reported by the national statistics. The remote sensing derived total area available for irrigation (TAAI), which does not consider intensity of irrigation, was 101 million hectares (Mha) using 10-km and 113 Mha using 500-m. The AIAs, which considers intensity of irrigation, was 132 Mha using 10-km and 146 Mha using 500-m. In contrast the IPU, an equivalent of AIAs, as reported by MoWR was 83 Mha. There are “large variations” in irrigated area statistics reported, even between two ministries (e.g., Directorate of Statistics of Ministry of Agriculture and Ministry of Water Resources) of the same national system. The causes include: (a) reluctance on part of the states to furnish irrigated area data in view of their vested interests in sharing of water, and (b) reporting of large volumes of data with inadequate statistical analysis. Overall, the factors that influenced uncertainty in irrigated areas in remote sensing and national statistics were: (a) inadequate accounting of irrigated areas, especially minor irrigation from groundwater, in the national statistics, (b) definition issues involved in mapping using remote sensing as well as national statistics, (c) difficulties in arriving at precise estimates of irrigated area fractions (IAFs) using remote sensing, and (d) imagery resolution in remote sensing. The study clearly established the existing uncertainties in irrigated area estimates and indicates that both remote sensing and national statistical approaches require further refinement. The need for accurate estimates of irrigated areas are crucial for water use assessments and food security studies and requires high emphasis."
The Use of Remote Sensing Data for Drought Assessment and Monitoring in Southwest Asia
(2004) Thenkabail, Prasad; Gamage, M. S. D. N.; Smakhtin, Vladimir
"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."