Interannual variability and ensemble forecast of upper Blue Nile basin Kiremt season precipitation
Interannual variability and ensemble forecast of upper Blue Nile basin Kiremt season precipitation
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DOI：
10.1175/jhm580.1
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发表时间：
2007-06-01
影响因子：
3.8
通讯作者：
Rajagopalan, Balaji
中科院分区：
文献类型：
--
作者：
Block, Paul;Rajagopalan, Balaji
埃塞俄比亚的农业和尼罗河流量严重依赖于青尼罗河上游流域的基列姆季（6月至9月）降水，分别作为雨水灌溉和河流流量的一种手段。气候诊断表明，厄尔尼诺-南方涛动现象是该盆地季节性降水年际变化的主要驱动因素。一个赛季（3月至5月）的季节性降水的主要预测者确定的大尺度海洋-大气-陆地系统，包括海平面压力，海面温度，位势高度，气温，和帕尔默干旱严重程度指数。提出了一种基于局部多项式回归的非参数集合预报方法。该方法是数据驱动的，易于实现，并提供了一个灵活的框架，能够捕捉任何任意的特征（线性或非线性）存在于数据中，相比传统的线性回归。由广义交叉验证（GCV）标准确定的预测因子的最佳子集是从潜在的大规模预测因子中选择的。还提供了一种将季节降水预报分解为月度预报的简单方法。与埃塞俄比亚国家气象局目前使用的气候预测相比，交叉验证的预测显示出很高的技能。这种集合预报框架可以作为流域内水资源规划和管理的有用工具。
Ethiopian agriculture and Nile River flows are heavily dependent upon the Kiremt season (June-September) precipitation in the upper Blue Nile basin, as a means of rain-fed irrigation and streamflow contribution, respectively. Climate diagnostics suggest that the El Nino-Southern Oscillation phenomenon is a main driver of interannual variability of seasonal precipitation in the basin. One-season (March-May) lead predictors of the seasonal precipitation are identified from the large-scale ocean-atmosphere-land system, including sea level pressures, sea surface temperatures, geopotential height, air temperature, and the Palmer Drought Severity Index. A nonparametric approach based on local polynomial regression is proposed for generating ensemble forecasts. The method is data driven, easy to implement, and provides a flexible framework able to capture any arbitrary features (linear or nonlinear) present in the data, as compared to traditional linear regression. The best subset of predictors, as determined by the generalized cross-validation (GCV) criteria, is selected from the suite of potential large-scale predictors. A simple technique for disaggregating the seasonal precipitation forecasts into monthly forecasts is also provided. Cross-validated forecasts indicate significant skill in comparison to climatological forecasts, as currently utilized by the Ethiopian National Meteorological Services Agency. This ensemble forecasting framework can serve as a useful tool for water resources planning and management within the basin.