Multi-Timescale Variations in Cloud Water Resources and Their Relationships with Climatic and Environmental Factors over Northwest China

Northwest China is characterized by severe water scarcity, and cloud water represents an important potential supplement to regional water availability. Cloud water path is a key physical parameter for quantitatively characterizing cloud water resources; understanding its variability and associated influencing factors is essential for the scientific assessment and sustainable utilization of regional cloud water resources. In this study, ERA5 and JRA-3Q reanalysis datasets (1960–2025) and satellite cloud products from MODIS and Cloud_cci (2003–2016) were used to evaluate the consistency of multi-source datasets in capturing cloud water path variations. Following the assessment of ERA5 applicability through multi-source comparisons, trend analysis, change-point detection, and ensemble empirical mode decomposition (EEMD) were applied to characterize the multi-timescale variability of cloud water path. Furthermore, the associations of cloud water path variability with climatic and environmental factors, including atmospheric circulation, aerosol optical depth (AOD), global mean surface temperature (GMST) anomaly, and the El Niño–Southern Oscillation (ENSO), were investigated. The results indicated these datasets generally agreed on the temporal variability of cloud water path, whereas differences were found in the absolute ice water path (IWP) and total cloud water path (CWP) values and estimated long-term trends. IWP contributed substantially to CWP variability across most timescales, while the long-term evolution of CWP reflected changes in both liquid water path (LWP) and IWP. LWP, IWP, and CWP showed gradual increasing tendencies, with no significant change points detected. EEMD analysis suggested variability components at approximately 3-year and 7–9-year timescales with relatively large variance contributions, although these components were not statistically significant. Cloud water path variability showed different relationships with climatic and environmental factors. The IWP IMF1 component, with an approximately 3-year timescale, exhibited a weak positive association with the mid-latitude westerly index, whereas no stable linear relationships were detected between cloud water path and summer monsoon or ENSO variability. IWP and CWP showed significant seasonal correlations with AOD, which may largely be attributable to their shared seasonal variations. After detrending, IWP exhibited a weak negative correlation with GMST anomaly.