Browsing by Author "Dheeravath, Venkateswarlu"

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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."