Development of drought index and quantitative assessment of spatiotemporal distribution characteristics of the Loess Plateau using multi-source remote sensing

Abstract

Drought significantly affects water and carbon cycles of the terrestrial ecosystems, particularly in arid and semi-arid regions. However, drought monitoring using remote sensing approaches remains limited, because remote sensing-based drought indices lack explicit physical mechanisms. To address this gap, this study developed a comprehensive drought index (CDI) by integrating the normalized difference drought index (NDDI), soil moisture monitoring index (SMMI), and temperature vegetation drought index (TVDI), while explicitly accounting for the temporal evolution and physical drivers of drought. Using Theil-Sen Median trend analysis and the Mann-Kendall test, this study quantified the spatiotemporal dynamics of drought across the Loess Plateau during 2001–2022. Combined with Hurst index analysis, this study further assessed the long-term persistence and projected future drought trends. The results showed that: (1) CDI effectively reflected regional soil drought conditions, and exhibited a significant negative correlation with in situ soil moisture measurements (R2 = 0.71). (2) The Loess Plateau experienced moderate drought, with a slow declining trend in dryness. (3) Spatially, drought conditions migrated seasonally; severe drought occurred predominantly in spring and summer, whereas moderate drought prevailed in autumn and winter. Drying trends dominated the northwestern and southeastern Loess Plateau, while the central region along the northeast-southwest exhibited an obvious wetting trend. (4) Hurst index suggested an overall trend toward drier conditions in the future, with larger humidifying areas in autumn and winter than in spring and summer. This study advances drought monitoring methodology and provides data support for drought monitoring and early warning in the Loess Plateau.