The United Graduate School of Agricultural Sciences, Tottori University, 4-101 Koyama-Minami, Tottori 680-8553, Japan; Faculty of Civil and Water Resource Engineering, Bahir Dar Institute of Technology, Bahir Dar University, P.O. Box 26, Bahir Dar, Ethiopia.
Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680-0001, Japan.
Sci Total Environ. 2019 Nov 1;689:347-365. doi: 10.1016/j.scitotenv.2019.06.338. Epub 2019 Jun 27.
Land use/land cover (LULC) change and climate variability are two major factors controlling hydrological responses. The present study analyzed the separate and combined effects of these two factors on annual surface runoff and evapotranspiration (ET) after validating the selected models in three drought-prone watersheds of the Upper Blue Nile basin: Kasiry (highland), Kecha (midland), and Sahi (lowland). LULC maps were produced from aerial photographs and very-high-resolution satellite images from 1982, 2005/06 and 2016/17. During 1982-2016/17 the area covered by natural vegetation showed dramatic decreases, ranging from 60.2% in Kasiry to 51.8% in Sahi. In contrast, increases in cultivated land ranged from 36.7% in Kasiry to 279.6% in Sahi; the smaller increase in Kasiry resulted from the conversion of a portion of the cultivated land to an Acacia decurrens plantation after 2006. The observed LULC changes over the study period resulted in runoff increases ranging from 4% in Kecha to 28.7% in Kasiry. Climate variability in terms of annual rainfall had no significant effect on estimated runoff; whereas both LULC change and climate variability had significant effect on estimated ET. Though climate variability increased ET from 33.6% in Kecha to 42.1% in Kasiry, the LULC change related to the reduction in natural vegetation had an offsetting effect, which led to overall decreases in ET ranging from 15.8% in Kasiry to 32.8% in Kecha watershed. As changes in LULC and climate are expected to intensify in the future, it is important to study further hydrological responses considering these changes to devise future sustainable land and water management strategies.
土地利用/土地覆被（LULC）变化和气候变率是控制水文响应的两个主要因素。本研究在分析了三个易旱尼罗河流域的模型验证后，分析了这两个因素对年地表径流量和蒸散量（ET）的单独和综合影响：上尼罗河流域的 Kasiry（高地）、Kecha（中地）和 Sahi（低地）。LULC 图由 1982 年、2005/06 年和 2016/17 年的航空照片和超高分辨率卫星图像生成。在 1982 年至 2016/17 年期间，天然植被覆盖面积大幅减少，范围从 Kasiry 的 60.2%到 Sahi 的 51.8%。相比之下，耕地面积从 Kasiry 的 36.7%增加到 Sahi 的 279.6%；由于 2006 年后部分耕地转变为金合欢种植园，Kasiry 的增幅较小。在研究期间观察到的 LULC 变化导致径流量增加，范围从 Kecha 的 4%到 Kasiry 的 28.7%。年度降雨量方面的气候变率对估计的径流量没有显著影响；而 LULC 变化和气候变率对估计的 ET 都有显著影响。尽管气候变率使 ET 从 Kecha 的 33.6%增加到 Kasiry 的 42.1%，但与天然植被减少相关的 LULC 变化具有抵消作用，导致 ET 总体减少，范围从 Kasiry 的 15.8%到 Kecha 的 32.8%。由于未来 LULC 和气候的变化预计会加剧，因此考虑到这些变化研究进一步的水文响应，以制定未来可持续的土地和水资源管理策略非常重要。
