Characteristics and determining factors of spring-summer consecutive drought variations in Northwest China

Abstract

Northwest China (NWC, defined by its administrative division) is an arid and semi-arid region where continuous drought occurs in spring and summer that severely affects crop growth and yields. However, the characteristics of spring-summer consecutive drought (SSCD) in NWC remain unknown. Based on daily observation data from 118 stations in NWC for the period 1961–2017, we investigated the variations in SSCD, as defined by the standardized precipitation evapotranspiration index (SPEI), and their determining factors. The SSCD intensity in NWC underwent a two-stage change rather than a sustained non-significant decrease during 1961–2017. Specifically, this intensity significantly decreased before 1993 (−0.19 decade−1; p < 0.05) and increased thereafter (0.21 decade−1; p < 0.05). The variations in SSCD in NWC were primarily determined by the variations in potential evapotranspiration (ET0). The decrease and increase in ET0 (−19.52 mm decade−1 and 10.77 mm decade−1, respectively; p < 0.05) dominated those of SSCD in NWC during 1961–1993 and 1994–2017, respectively, with respective explanatory variances of 99.6% and 93.2%. Furthermore, the decrease in wind speed (−0.14 m s−1 decade−1; p < 0.05) dominated that in ET0 before 1993, whereas the decrease in relative humidity (−1.47% decade−1; p < 0.05) and the weak recovery of wind speed (−0.06 m s−1 decade−1; p < 0.05) jointly dominated the increase in ET0 after 1993. Along with the increased SSCD after 1993, significant changes also occurred in the atmospheric circulation. An intensified anticyclonic anomaly occurred to the west of NWC, which provided a favorable circulation background for the increase in SSCD in NWC after the early 1990s. These findings provide a basis for further understanding drought and sustainable agricultural development in NWC under climate change.