肯尼亚雨水集流利用现状及思考

雨水集流作为一项古老技术,已有上千年的历史。由于干旱缺水和缺乏天然的储水介质,雨水集流在肯尼亚具有非常重要的特殊意义。本文从庭院集雨、农田集雨、流域集雨及集雨的区域差异等方面,对肯尼亚的雨水集流现状进行了分析;并从区域水循环与水量平衡的角度,探讨了降雨、入渗、径流及蒸发的关系。最后指出,通过不同形式的雨水集流,减少无效蒸发,特别是无效的水面蒸发,是增加水资源总量的关键;而科学利用天然的储水介质与合理开发人工的储水介质,是提高水资源可利用量的关键。雨水集流利用在肯尼亚生活用水方面已相当普遍,技术也相对较为成熟,但是在年降雨量不足500 mm的旱区农业生产方面,还有很大的发展空间,目前面临的主要问题是,如何解决旱区降雨集流效率偏低,以及有限降雨资源的合理储蓄与高效利用。鉴于农田土壤对降雨再分配调蓄能力较低的缘故,通过在农田内开挖沟槽,进行降雨资源的短期储蓄与调控,将生育期前段多余的降雨资源留到无降雨的后段使用,是实现作物生育期内水分供需平衡的关键。本研究为充分发挥雨水集流在肯尼亚旱区农业生产中的积极作用提供了参考。

Utilization state and thought on rainwater harvesting in Kenya

Kenya is in East Africa and has a tropical monsoon climate. Prolonged droughts and unexpected shifts in normal weather patterns are the main hurdles preventing Kenya from realizing poverty eradication, food security, and environmental sustainability. Rainwater harvesting, as a highly efficient old economic technique of saving additional water, has a history spanning over thousands of years. Due to lack efficient medium for natural rainwater storage in Kenya, rainwater harvesting has become a critical mode of fighting off drought in the country. A systemic analysis of the state of rainwater harvesting was conducted along with the local climatic, hydrological and geographic conditions for realistically determining highly efficient storage and use of rainwater. In this study, based on virtual field trips and discussions with local farmers and researchers in educational institutions, the state of utilization of various rainwater harvesting systems in Kenya was evaluated. The study analyzed the differences in space and time in rainwater collection methods at courtyard, farmland and basin levels. The study also determined rainfall, infiltration, runoff and evaporation in relation to regional water cycle and water balance. The analysis showed that it was critical to increase the total volume of water resources by using various rainwater harvesting techniques, and to reduce invalid evaporation, especially unproductive water evaporation. The main way of increasing the volume of available water resources was by scientifically using natural and artificial water storage media. Even though rainwater harvesting systems that had relatively mature technologies were very common in daily domestic life, there was still big development space for improvement in less than 500 mm annual rainfall in agricultural production area. The prevailing problems faced in the region were how to improve the low efficiency of rainwater harvesting, and to reasonably store and efficiently use collected rainwater in the arid region. Given the weak regulation and storage capacity of the local soil to redistribute rainwater, it was necessary to balance water supply and demand during crop growth period. One way of doing this was by regulating short-term storage and rainwater by excavating trenches in farmlands. This implies the early harvest of extra rainwater in raining season and then irrigated crops at the later stages of growth when there was no rainfall. The suggestions and recommendations in this research will lay the reference needed to increase the role of rainwater harvesting in agricultural production in Kenya and in other arid and semi-arid regions around the globe.