中亚五国棉花和冬小麦需水量的变化及预测

农业灌溉用水是中亚地区最主要的水资源利用方式,灌溉用水量的变化直接影响中亚地区水资源消耗量,进而影响水资源管理和配置。作物需水量是衡量农业灌溉用水量的直接指标,为此本文以中亚主要作物棉花和冬小麦为研究对象,分析了2006—2015年中亚地区灌溉农业用地,以及棉花和冬小麦的需水量变化,并利用CA_Markov方法预测了2030年灌溉农地的变化,进而分析了未来中亚地区农业需水量的状况。研究表明,2006—2015年,中亚地区灌溉农田面积总体增加492km~2,其中哈萨克斯坦、吉尔吉斯斯坦和土库曼斯坦均有所增加,但塔吉克斯坦和乌兹别克斯坦有所减少。2006—2015年,棉花需水量只在土库曼斯坦和哈萨克斯坦东部地区显著增加(2.5～4.3 mm·a~(-1)),在吉尔吉斯斯坦显著减少,并且是唯一呈现总体减少趋势的国家。冬小麦需水量在土库曼斯坦明显增加(10.0mm·a~(-1))。至2015年,土库曼斯坦的棉花总灌溉水量增幅最大(3.44%),其他4个国家变化较小。中亚五国冬小麦的总灌溉水量均呈上升趋势; 2030年,土库曼斯坦是唯一灌溉农业用地增加的国家,棉花和冬小麦的总灌溉水量均明显增加,棉花灌溉水量增加约28km~3,冬小麦增加约17 km~3。

Variations in and predictions of irrigation water requirements of cotton and winter wheat in Central Asia

Agricultural irrigation consumes most of the fresh water in Central Asia (CA). Therefore, changes in irrigation water use have direct effects on water resources, water management, and water resource allocation. The crop water requirement (CWR) is a direct indicator of agricultural irrigation; the CWR of cotton and winter wheat (the two main crops of CA) was investigated in this study. Based on the CWR method proposed by the Food and Agriculture Organization (FAO), the CWR and total irrigation water of cotton and winter wheat in irrigated croplands in CA were calculated from 2006 to 2015. Changes in the irrigation cropland area and cotton and winter wheat CWR from 2006 to 2015 were also analyzed. To assess the near-future status of agricultural water resources in CA, the irrigated cropland area in 2030 was predicted via the CA_Markov method, and the CWR of the two crops in 2030 was explored. Land cover data from the European Space Agency Climate Change Initiative (ESA CCI) was used to identify the irrigation cropland. Digital Elevation Model (DEM) data from the Shuttle Radar Topography Mission (SRTM), population density data from the Socioeconomic Data and Applications Center, and river vector data from Natural Earth were used to predict the irrigated cropland area in 2030. The results showed that irrigated cropland in CA increased by 492 km² from 2006 to 2015, with increases in Kazakhstan, Kyrgyzstan, and Turkmenistan, and decreases in Tajikistan and Uzbekistan. The CWR of cotton and winter wheat tended to increase in most areas. The CWR of cotton increased rapidly from 2006 to 2015 (2.5-4.3 mm·a^-1) in Turkmenistan and eastern Kazakhstan but decreased in Kyrgyzstan. For winter wheat, the largest CWR increase (10 mm·a^-1) was in Turkmenistan, and no changes were observed in the other four CA countries. In 2030, the irrigated cropland in Turkmenistan was predicted to increase by 30.5% compared with 2015, and Turkmenistan is the only country to increase irrigated croplands in the near future. This will lead to a notable increase in the CWR of cotton and winter wheat. The results showed that there will be an increase of 28 km³ for the total irrigation water of cotton and 17 km³ for winter wheat in Turkmenistan in 2030. The other four countries were predicted to have decreased irrigation cropland compared with 2015, with decreases of 7.4%, 5.8%, 3.4%, and 0.9% for Uzbekistan, Tajikistan, Kazakhstan, and Kyrgyzstan, respectively. Although Uzbekistan is predicted to decrease irrigation cropland in 2030, the increase in winter wheat CWR will increase the total irrigation water by 10-14 km³. Therefore, Uzbekistan and Turkmenistan will face severe shortages in irrigation water resources in the near future.