Influence of the accuracy of reference crop evapotranspiration on drought monitoring using standardized precipitation evapotranspiration index in mainland China

Abstract

Abstract Reference crop evapotranspiration ( ET 0 ) estimation accuracy strongly affects the accuracy of drought monitoring using the standardized precipitation evapotranspiration index (SPEI). The FAO56 Penman–Monteith (the reference method here), Irmak, Berti, Priestley–Taylor, and Valiantzas methods were used to compute ET 0 and subsequently SPEI at 1‐, 3‐, and 12‐month timescales during 1961–2016 at 763 weather stations in China. The spatiotemporal variations in the climatic variables and ET 0 , D (= P − ET 0 ) and SPEI with five ET 0 estimators (hereafter SPEI PM , SPEI IRA , SPEI PT , SPEI MHS , and SPEI Val ) were investigated. The cumulative frequency and periods (using the Morlet wavelet analysis) of the annual SPEIs were analyzed. The results showed that, corresponding to the P , ET 0 , and D , drought severity was characterized by large seasonal and regional differences using SPEI PM , SPEI IRA , SPEI PT , SPEI MHS , or SPEI Val , especially in northwestern China, the Inner Mongolia region, and the Qinghai–Tibetan Plateau ( P < 500 mm/yr). Additionally, the effects of the different ET 0 equations on the minimum SPEI and frequency values were large in these drier subregions but generally small in other regions. Meanwhile, an increased ET 0 prediction accuracy did not automatically lead to an improved SPEI accuracy in regions P > 500 mm/yr. With respect to the averaged values for Subregion 1 ( P < 134 mm/yr), although the vibration intensities and spectra were visually similar for different SPEIs, the periodical signals differed. Regional climatic conditions have a significant impact on the SPEI estimates in regions characterized by P (<500 mm/yr); we therefore suggest that the ET 0 equations for drought analysis with SPEI should be carefully selected.