Seasonal single-peak and double-peak patterns in precipitation and terrestrial water storage, and their controlling mechanisms over Indochina Peninsula

Being in a transition zone of Asian monsoons, the water resources of the Indochina Peninsula (ICP) is highly sensitive to climate change and variability. Potential shifts in regional precipitation patterns and terrestrial water storages (TWS) are critical to the resilience of the regional water resources. Though the seasonal variations in precipitation were well documented, less attention has been given to the differences between single-peak and the double-peak patterns in precipitation and TWS, and
their climatic and geomorphologic controlling factors. Using trend detection and principal component analysis (PCA), this study explores long-term changes, seasonal single- and double-peak patterns of precipitation and TWS. We found that TWS experienced an increasing long-term trend in the central ICP, which may be linked to the bowl-shaped topography holding the water continuously. Meanwhile, we found a decline in TWS in northern and southern ICP regions, which may be associated with rising temperature and decreasing precipitation. We then examine the two dominant modes of total precipitation (TWS) variability, accounting for about 86% (96%) of the total variance. The first mode describes coherent changes in precipitation (TWS) across almost the entire ICP, which are characterized by single-peak seasonal cycle centered on June-August (August-September) and is mainly linked to the Indian monsoon (IM). The second mode emphasizes on southern precipitation (TWS), which is characterized by a double-peak seasonal cycle centered on May and September-October (May-June and November-December) and predominantly affected by the West North Pacific monsoon (WNPM). Moreover, El Niño-Southern Oscillation (ENSO) contributes more to the double-peak pattern in precipitation and TWS compared to their single-peak pattern. Overall, this study unravels the long-term trends, seasonal single- and double-peak patterns in precipitation and TWS over the ICP and examines the underlying climate and geographical mechanisms controlling them. It holds significant implications for fostering sustainable regional development and enhancing water resilience.