基于SPI和云模型的海河平原区干旱特征研究

Drought Characteristics of Haihe Plain Based on SPI and Cloud Model

摘要:

根据海河平原20个气象站1955—2019年逐日降水量计算了年尺度和季尺度的标准化降水指数(SPI)，对各尺度不同等级的干旱频率及其时空特征进行分析；以年尺度SPI为样本，采用正态云发生器算法和多步还原逆向云变换算法构建云模型，分析了干旱的随机性和稳定性。结果表明，海河平原区干旱频率主要分布区间为[0.28,0.31]，呈现轻旱高频、重旱低频的特点；春旱发生频率最高，冬旱频率最小，夏季地区间及年际间差异最大。年际间SPI云模型的3个特征参数均呈减小趋势，其中熵呈显著减小趋势，且超熵与熵呈显著正相关，即SPI分布的随机性和不均匀性变化趋势一致；空间上各站点超熵和熵则呈极显著负相关，随机性和不均匀性呈相反趋势；云特征的年际差异大于站点间差异，即云模型能够更好地反映区域年际间SPI在空间上的随机性和稳定性。海河平原整体上有趋于干旱的趋势，各站点SPI的随机性显著减小，且变化趋于稳定。

Abstract:

According to the daily precipitation of 20 meteorological stations in Haihe Plain from 1955 to 2019, the standardized precipitation index (SPI) on annual scale and seasonal scale was calculated, and the drought frequency and spatial and temporal characteristics of different levels on each scale were analyzed. Taking annual scale SPI as the sample, the normal cloud generator algorithm and the multi-step restoring reverse cloud transformation algorithm were used to construct the cloud model to analyze the randomness and stability of drought. The results showed that the drought frequency in Haihe Plain was mainly between 0.28 and 0.31, with the characteristics of high frequency of light drought and low frequency of heavy drought. The frequency of spring drought was the highest and winter drought was the lowest. The differences between regions and between years were the greatest in summer. The three characteristic parameters of the interannual SPI cloud model were all showed decreasing trends, in which the entropy significantly was decreased and the superentropy was significantly and positively correlated with the entropy, that was, the randomness and inhomogeneity of the SPI distribution showed a consistent trend. In space, the superentropy and entropy of each station showed a very significant negative correlation, the randomness and inhomogeneity showed an opposite trend. The inter-annual differences of cloud characteristics were greater than the inter-site differences, that was, the cloud model can better reflect the randomness and stability of regional inter-annual SPI in space. Haihe Plain tended to be drier in general, and the randomness of SPI of each station was decreased significantly and tended to be stable and uniform.