Geography: 月度潜在蒸散量

月度潜在蒸散量（Vicente-Serrano，庄少伟，有删改）：

\[{P_{ei}} = \left\{ {\begin{array}{*{20}{c}} 0&{{T_i} \le 1}\\ {1.6d{{\left( {\frac{{10{T_i}}}{I}} \right)}^a} \times 10}&{1 < {T_i} \le 26.5}\\ {{a_1} + {a_2}{T_i} + {a_3}T_i^2}&{{T_i} > 26.5} \end{array}} \right.\] \[a = 0.49239 + 1.792 \times {10^{ - 2}}I - 7.71 \times {10^{ - 5}}{I^2} + 6.75 \times {10^{ - 7}}{I^3}\] \[I = \sum\limits_{i = 1}^{12} {{I_i}} \] \[{I_i} = \left\{ {\begin{array}{*{20}{c}} 0&{{T_i} \le 0}\\ {{{\left( {\frac{{{T_i}}}{5}} \right)}^{1.514}}}&{{T_i} > 0} \end{array}} \right.\] \[\begin{array}{l} {a_1} = - 415.8547\\ {a_2} = 32.2441\\ {a_3} = - 0.4325 \end{array}\]

式中：d为每月的天数除以30（无量纲）；T_i为第i月平均温度（°C），I_i为第i月加热指数（Heat Index）;I为年加热指数；a、a₁、a₂和a₃均为计算过程中间的系数。

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References

[1] 庄少伟. 基于标准化降水蒸发指数的中国区域干旱化特征分析[D]. 兰州:兰州大学, 2013.

[2] Vicente-Serrano SM,Beguería S, López-Moreno JI. A Multiscalar Drought Index Sensitive to Global Warming: The Standardized Precipitation Evapotranspiration Index[J]. 2009, 23(7):1696-1718.