The sensitivity of the PDSI to the Thornthwaite and Penman‐Monteith parameterizations for potential evapotranspiration
The sensitivity of the PDSI to the Thornthwaite and Penman‐Monteith parameterizations for potential evapotranspiration
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DOI：
10.1029/2010jd015001
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发表时间：
2011-02
影响因子：
--
通讯作者：
G. Schrier;P. Jones;K. Briffa
中科院分区：
文献类型：
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作者：
G. Schrier;P. Jones;K. Briffa
[1] 潜在蒸散量 (PET) 是帕尔默干旱严重度指数 (PDSI) 的输入之一。计算 PDSI 的常用方法是使用 Thornthwaite 方法来估计 PET，因为它易于获得输入数据：月平均温度。基于 Penman 型方法的 PET 估计被认为在物理上更加真实，但需要更多样化的输入数据。本研究使用 PET 的两种估计值来评估全球 PDSI 地图的差异。基于替代 Thornthwaite 和 Penman-Monteith 的年度累积 PET 估计，参数化具有非常不同的幅度。然而，我们表明，基于两个 PET 估计的 PDSI 值在相关性、区域平均值、趋势以及识别极端干燥或潮湿月份方面非常相似。对 PET 计算方法不敏感的原因与简单水平衡模型中的计算有关，该模型是 PDSI 算法的核心。结果表明，在许多地区，实际蒸散量受到土壤水分可用性的限制，并且与其潜在值相比，实际蒸散量明显较低。在其他地区，水平衡确实发生了变化，但 PDSI 计算的核心数量通过构建反映了实际降水量，这使得它对使用 Thornthwaite PET 而不是 Penman-Monteith PET 在很大程度上不敏感。第二个原因是，与降水的主要影响相比，PET 作为 PDSI 算法中缩放参数的输入的影响非常小。
[1] Potential evapotranspiration (PET) is one of the inputs to the Palmer Drought Severity Index (PDSI). A common approach to calculating PDSI is to use the Thornthwaite method for estimating PET because of its readily available input data: monthly mean temperatures. PET estimates based on Penman-type approaches are considered to be more physically realistic, but require more diverse input data. This study assesses the differences in global PDSI maps using the two estimates for PET. Annually accumulated PET estimates based on alternative Thornthwaite and Penman-Monteith, parameterizations have very different amplitudes. However, we show that PDSI values based on the two PET estimates are very similar, in terms of correlation, regional averages, trends, and in terms of identifying extremely dry or wet months. The reason for this insensitivity to the method of calculating PET relates to the calculations in the simple water balance model which is at the heart of the PDSI algorithm. It is shown that in many areas, actual evapotranspiration is limited by the availability of soil moisture and is at markedly lower levels compared to its potential value. In other areas, the water balance does change, but the quantity central to the calculation of the PDSI is, by construction, a reflection of the actual precipitation, which makes it largely insensitive to the use of the Thornthwaite PET rather than the Penman-Monteith PET. A secondary reason is that the impact of PET as input to a scaling parameter in the PDSI algorithm is very modest compared to the more dominant influence of the precipitation.