EVALUATION OF WINTER WHEAT YIELDS USING SPI AND SPEI AT 10-DAILY SCALES

Xiangying Xu,∗,∗∗,∗∗∗,∗∗∗∗ Xinkai Zhu,∗,∗∗∗ Yonglong Zhang,∗∗∗∗ Chunyan Li,∗,∗∗∗ Jinfeng Ding,∗,∗∗∗ Junwu Zhu,∗∗∗∗ Bin Li,∗∗∗∗ and Wenshan Guo,∗,∗∗∗

Keywords

Standardized precipitation index, standardized precipitation evapo- transpiration index, potential evapotranspiration, wheat yield ∗ Jiangsu Key Laboratory of Crop Genetics and Physiology, Yangzhou University, Yangzhou, 225009, China; e-mail: xux- iangying@126.com, {xkzhu, licy, jfdin, guows}@yzu.edu.cn ∗∗ Joint International Research Laboratory of Agriculture and Agri-Product Safety, the Ministry of Education of China, Yangzhou University, Yangzhou, Jiangsu, 225009, China ∗∗∗ Co-Innovat

Abstract

The standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI) are two widely used drought indices with multiple timescales to evaluate crop yields as well as to monitor dry/wet conditions in agriculture. The traditional indices are mainly based on monthly scales, but water stresses lasting for a few days may cause damage for most of the crops, including winter wheat. Therefore, 10-daily (dekad) scales of SPI and SPEI are calculated in this study within Jiangsu province of China to investigate the effectiveness of the drought indices in evaluating winter wheat yields. China Meteorological Assimilation Driving Datasets (CMADS V1.0) are used in calculation. Hargreaves (HG) and Penman–Monteith (PM) methods are adopted to obtain the potential evapotranspiration (ET0) for SPEI. Correlation analysis and regression analysis are carried out between de-trended wheat yields and the indices. The results show that SPI, SPEIHG, and SPEIP M can represent consistent moisture differences between the northern sites and southern sites of Jiangsu. Two most relevant sequences of each index are used to fit the wheat yields in Northern and Southern Jiangsu. The results of goodness of fit (R2) are between 0.53 and 0.66 in Northern Jiangsu and between 0.07 and 0.09 in Southern Jiangsu, which suggest that indices with dekad scales are more suitable for wheat yield evaluation of the Northern Jiangsu than the Southern Jiangsu in the study period. In addition, the performance of SPI, SPEIHG, and SPEIP M is close to each other. Therefore 10-daily indices are appropriate to reflect the water conditions for wheat production, especially in Northern Jiangsu.

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