Dry–Wet Changes in a Typical Agriculture and Pasture Ecotone in China between 1540 and 2019

Exploring periodic dry–wet changes is an important topic in climate change research due to its impact on drought and flood disasters. The purpose of this research was to determine the occurrence law of dry–wet changes in China on a scale of several hundred years, using the example of transitional zones. In this study, we analyzed typical areas of the ecotone between agricultural land and pasture along the Great Wall of China. The ring width index of Carya cathayensis was fitted with the March–August Palmer drought severity index (PDSI₃₈). The PDSI₃₈ was divided into different periods using the stepwise function fitting method. The results indicated that there were two dry periods and one wet period in the region from 1543 to 2019. In each dry and wet period, there were also different temporal periods, including long (decades), intermediate (ten years), and short periods (several years). Drought represents a significant threat to agricultural production in China. In the first dry period (1543–1756), four periods with low PDSI₃₈ values (1633–1635, PDSI₃₈ = −1.71; 1636–1939, PDSI₃₈ = −3.35; 1640–1642, PDSI₃₈ = −4.68; and 1643–1645, PDSI₃₈ = −2.92) occurred, during which severe droughts (PDSI₃₈ < −4) lasted for 13 years. The dry–wet change showed the characteristics of a 12-year or multiple 12-year cycle. The results can be used to prepare to effectively address extreme drought scenarios worldwide in the future.