A stone-carved climate record
In Myanaung Township, situated on the banks of the massive Ayeyarwady River, local pagodas hold an unusual and scientifically valuable dataset. For centuries, possibly as long as 500 years, monks and local communities have carved inscriptions into the stone structures of pagodas to mark the maximum height of major flood events. These markings, often consisting of a simple line and a date in the Burmese script, form one of the longest continuous, non-instrumental hydrological records in Southeast Asia.
This unintentional archive provides a year-by-year account of the Ayeyarwady River's behavior, predating modern hydrological monitoring by centuries. Each inscription is a data point, capturing the peak of the monsoon season's inundation. Researchers have meticulously documented these markings, translating the dates and measuring the heights to convert the historical records into a standardized format suitable for statistical analysis. This process is a powerful tool for understanding long-term environmental change.
Decoding the past to predict the future
Analysis of the 500-year flood record reveals a clear and concerning trend: the frequency of large floods in the Myanaung area has been increasing. While the Ayeyarwady Delta has always been shaped by the river's powerful annual flood pulse, the data inscribed on the pagodas show that severe inundation events are becoming more common in recent decades.
Scientists connect this increase in flood frequency to large-scale land-use changes far upstream. Extensive deforestation in the upper Ayeyarwady basin is a primary cause. Forests act as natural sponges, absorbing monsoon rains and releasing the water slowly. When forests are cleared, rainwater runs off the land much more quickly, carrying loose soil and sediment into the river. This increased sediment load, or silt, gradually raises the riverbed downstream. A shallower river channel has a reduced capacity to carry water, causing it to overtop its banks more easily and frequently during the annual monsoon, leading to the kind of floods recorded on the Myanaung pagodas. The data from these ancient inscriptions, therefore, documents local history and reflects the cascading environmental consequences of deforestation hundreds of kilometers away.