Spatial Calculation of the Standardized Precipitation Evapotranspiration Index

The Standardized Precipitation Evapotranspiration Index (SPEI) offers a more accurate representation of drought conditions compared to the Standardized Precipitation Index. This is because it incorporates evapotranspiration calculations, thus making it superior to the latter. For this study, we calculated the spatial distribution of the SPEI index over a 12-month period in a particular region. The results clearly depict alternating patterns of drought (in red) and moisture (in blue) in the area. For instance, from January 2000 to March 2003, the extent of the drought gradually expanded to cover the entire region by January 2002. The severity of the drought also deepened during this period. However, afterwards, the drought started to weaken, indicating a gradual diminishing trend.

Spatial calculation of the Standardized Precipitation Index

The Standardized Precipitation Index (SPI) is one of the metrics used to assess drought conditions. Because it only requires precipitation data and is relatively simple to calculate, it has gained widespread application. In this study, we calculated the SPI over a six-month timescale for a specific location, which revealed a clear alternation between wet (blue) and dry (red) periods.

Design: ANUSPLIN空间插值植被指数

Fig. 1

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Fig. 2

Meteorology: 土壤干燥度

Summary

土壤干燥度的计算采用修正的谢良尼诺夫模型，具体可表为：

\[D = 0.16 \cdot \frac{{{T_{ \ge 10^\circ {\rm{C}}}}}}{{{P_{ \ge 10^\circ {\rm{C}}}}}}\]

式中：D——干燥度；T——年大于10℃积温；P——全年大于10℃降水量之和，在干旱地区也可以近似约等于全年降水量。

Example

SoilDrought.rar.

References

[1] 胡云锋, 阿拉腾图雅, 艳燕, 于国茂. 内蒙古锡林郭勒生态系统综合监测与评估. 北京: 中国环境出版社, 2013. pp:213.

[2] 张国平, 张增祥, 刘纪远. 中国土壤风力侵蚀空间格局及驱动因子分析. 地理学报, 2001, 56(2):146~158.

[3] 曹祥会, 雷秋良, 龙怀玉, 等. 河北省土壤温度与干湿状况的时空变化特征. 土壤学报, 2015, 52(3):528~537.

Meteorology: 风场强度

Summary

风场强度是影响影响土壤颗粒能否被风力搬运的决定性因素。风场强度的大小可以利用对常规地面气象观测中有关风速、风向的观测数据进一步计算得到。

风场强度的计算采用美国农业部土壤风力侵蚀方程RWEQ中的相应公式：

\[W = \frac{{{n_d}}}{{500}} \cdot \sum\limits_{i = 1}^n {U \cdot {{\left( {U - {U_c}} \right)}^2}} \]

式中：W——风能强度因子，m³/s³；n——观测次数；n_d——观测活动包含天数；U——离地面2 m高处的风速；U_c——2 m高处的临界风速，一般设置为5 m/s。

Example

Practice.rar.包含ANUSPLIN批量并行插值代码

References

[1] 胡云锋, 阿拉腾图雅, 艳燕, 于国茂. 内蒙古锡林郭勒生态系统综合监测与评估. 北京: 中国环境出版社, 2013. pp:211~213.

[2] 巩国丽, 刘纪远, 邵全琴. 基于RWEQ 的20 世纪90 年代以来内蒙古锡林郭勒盟土壤风蚀研究. 地理科学进展, 2014, 33(6): 825~834.

[3] Feras Youssef, Saskia Visser, Derek Karssenberg, et al.. Calibration of RWEQ in a patchy landscape; a first step towards a regional scale wind erosion model. Aeolian Research, 2012, (3): 467~476.