Spatial Reconstruction of Precipitation and Temperature and Analysis of Drought Characteristics in the Shiyang River Basin

To reveal the spatiotemporal differentiation of precipitation, temperature and meteorological drought characteristics in the Shiyang River Basin, continuously reconstructed precipitation and temperature fields from 2004 to 2023 were used to analyze the spatial distribution, seasonal variation, and interannual variation in precipitation and mean temperature. The Standardized Precipitation Index (SPI) was used to characterize basin-scale meteorological dry–wet conditions, and Innovative Trend Analysis (ITA), the Mann–Kendall test, and Sen’s slope were combined to analyze trends in precipitation, temperature and meteorological drought. The results showed that the mean annual precipitation and mean temperature were 238.00 mm and 7.56 °C, respectively. Precipitation was higher in the southern mountainous areas and decreased toward the north, while temperature decreased with increasing elevation. Summer precipitation accounted for 54.70% of annual precipitation. Annual precipitation showed a non-significant upward trend (SITA = 1.5932, Mann–Kendall p = 0.721), whereas annual mean temperature showed a significant upward trend (Mann–Kendall p = 0.041, Sen’s slope = 0.046 °C yr−1). However, this warming signal is inherited from the gridded forcing and is not validated against station trends. Both SPI-3 and SPI-6 exhibited non-significant upward tendencies during 2004–2023 (Hamed–Rao modified MK p = 0.485 and 0.475, respectively); the statistical significance of these trends was evaluated using the Hamed–Rao modified Mann–Kendall test. SPI analysis indicated pronounced temporal variation and spatial heterogeneity in meteorological drought. Based on annual drought statistics, 2013 and 2023 were identified as the most severe drought years, with 2013 featuring the highest cumulative severity and drought area ratio, and 2023 the longest duration. Spatially, the reconstructed fields indicated potential drought signals in the central basin, while the southwestern mountains experienced milder conditions. These findings highlight the need for region-specific drought monitoring and adaptive agricultural water-resource allocation in the Shiyang River Basin.