Spatial Coherence and Non-Stationary Drought Dynamics in Water Management Basins of Northern and Central Kazakhstan

This study investigates the spatiotemporal variability, spatial consistency, and non-stationarity of meteorological and hydrological droughts in three major water management basins (WMBs) of northern and central Kazakhstan: Nura–Sarysu, Esil, and Tobyl–Torgai. Long-term instrumental observations from meteorological stations and hydrological gauges were used to calculate the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and Streamflow Drought Index (SDI). Structural changes were detected using the Pettitt, Buishand, and CUSUM tests, while spatial consistency was quantitatively assessed as the proportion of active meteorological stations simultaneously experiencing drought conditions. The results showed that major drought episodes represented spatially coherent regional events rather than isolated local anomalies; however, their spatial extent varied substantially among the basins. The highest synchronization of meteorological droughts was observed in the Esil WMB, whereas the Tobyl–Torgai WMB exhibited greater spatial heterogeneity. Statistically significant structural changes were identified in both meteorological and hydrological drought series; however, their timing and frequency differed among indices and basins, indicating pronounced temporal non-stationarity. A higher proportion of structural changes was identified for SPI-3 than for SPEI-3. However, this difference is interpreted as reflecting differences in the statistical behavior of the precipitation index and the climatic water balance index rather than direct evidence of the relative contributions of precipitation and atmospheric evaporative demand. SDI-12 exhibited more persistent and temporally smoothed hydrological drought dynamics compared with the short-term meteorological indices, while the timing of hydrological changes differed among river systems. The results demonstrate that drought development in Northern and Central Kazakhstan is characterized by spatial heterogeneity and temporal non-stationarity, while the joint interpretation of SPI, SPEI, and SDI provides a more comprehensive basis for basin-scale drought monitoring and adaptive water-resource management.