A study on agricultural land and water management against decrease of irrigation water supply - a case study of the lower Ili River basin, Kazakhstan

摘要

In the lower Ili River basin where climate is arid,large irrigated agriculture has been practiced since 1960's.Rising temperature and decreasing precipitation in Central Asia are predicted by the Fourth Assessment Report of the Intergovernmental Panel on Climate Change(IPCC).If the prediction happens,discharge of Ili River in summer season might decrease due to the decline of glacier area in the headwater region.In the irrigation district,a crop rotation system which combines paddy rice and field crops is practiced.Field crops use groundwater which has gone up to the root zone because of seepage from canals and paddy fields.If groundwater level falls because of decreasing irrigation water supply due to shortage of Ili River discharge,current irrigation methods might be unsustainable.It is therefore necessary to introduce appropriate management measures for control of groundwater level.As a first step towards the management of groundwater level,this study analyzed temporal and spatial distribution of groundwater level fluctuation.Additionally,it analyzed the condition of water supply to field crops by seepage from canals and paddy fields.The results are:(1)The distribution of groundwater level fluctuation was not uniform and fluctuating factors were different according to the location in the irrigation district;(2)The condition of water supply to field crops was affected by the position rather than the area of paddy fields.In response to reduction of irrigation water supply in the future,a revision of amount of irrigation water requirement,which currently is uniform to all paddy fields,for each location of paddy fields based on the spatial distribution of the paddy fields inside of the irrigation district,will be required.