Importance of water consumption by perennial vegetation in irrigated areas of the humid tropics: evidence from Sri Lanka |
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| Institution: | 1. Agricultural Research Organization (ARO), Fish and Aquaculture Research Station Dor, M.P. Hof HaCarmel, 30820 Israel;2. Israel Water Workers Association, Eyal, mid-Sharon 45480, Israel;1. NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki 305-8666, Japan;2. National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan;3. NARO Tohoku Agricultural Research Center, Agricultural Radiation Research Center, 50 Harajukuminami, Arai, Fukushima, Fukushima 960-2156, Japan;4. National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan;1. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, 1432 Ås, Norway;2. School of Environment Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia;3. Center for International Forestry Research, Bogor 16000, Indonesia;1. Delta-T Devices Ltd., 130 Low Road, Burwell, Cambridge, CB25 0EJ, UK;2. Rothamsted Research, West Common, Harpenden, St Albans, AL5 2JQ, UK;1. State Key Laboratory of Simulation and Regulation of Water Cycles in River Basins, China Institute of Water Resources and Hydropower Research, Beijing 100038, China;2. State Key Lab of Resources and Environmental Information Systems, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China |
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| Abstract: | In tropical, monsoon climates of South-East Asia, irrigation facilities supplement rain in the wet season and enable crops to be cultivated during the dry season. In the Dry Zone of Sri Lanka, 70% of the average annual rainfall of 1000 mm falls in a 3 month period. During the dry season, reference evapotranspiration has less rainfall — about 700 mm, indicating that much additional supply is meant to support crops, mainly paddy. In this climatic context, irrigation has dramatically changed the local environment, creating ecosystems quite similar to that of the wet zone to flourish. In these systems, recharge of shallow groundwater by percolation from irrigated fields, canals, and tanks, has provided a continuous supply of water for natural vegetation and homestead gardens. Much of the water used by this non-crop vegetation is beneficial. Growth of fruit and coconut trees can be quite profitable, while other trees enhance the environment.In 1998, IWMI performed a comprehensive water balance in the command area of the Kirindi Oya irrigation scheme, Sri Lanka, based on surface flow measurements, rainfall data, and estimation of crop water requirements. This water balance showed that evaporation consumed 78% of the total amount of water available for use. The amount of evaporation is split into process depletion (crops for 28%), direct evaporation from tanks (7%), inter-seasonal fallow (10%) and from non-crop vegetation for 55%.The main conclusion from this study is that perennial vegetation as the main component of non-crop vegetation, is a significant consideration in tropical humid environments in planning, management and performance assessment. Designers, managers, and researchers need to specifically incorporate the evaluation of evaporation by non-crop vegetation and perennial vegetation in their approach of water requirements. Further investigation is needed to estimate water consumption by land cover type to assess their respective beneficial use. |
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