Understanding severe drought events using dendrochronology in Cascade Lake Watershed, California

Droughts are frequent weather events in California. Tree-rings can provide information about past climate and drought beyond instrumental period at an annual timescale. We collected 44 tree-ring cores from 24 Jeffrey Pine ( Pinus jeffreyi Grev. & Balf.) trees located at the upper limit of their distribution in the Cascade Lake watershed, California to understand past extreme drought events. Tree-ring cores were processed with a standard method to enhance the visibility of the tree-rings and ring-width was measured with the Velmex tree-ring measurement system. Visual crossing dating and statistical packages (COFECHA, ARSTAN, and dplR ) were used to remove cross dating and age-related error. We developed a 294 year-long (1725-2018) tree-ring chronology of Jeffery Pine for this area. Low growth events correspond with 20 th -century drought events and precipitation records from California. Based on this strong correlation we have inferred that years 1729, 1730, 1752, 1753, 1757, 1763, 1771, 1777, 1781-83, 1796 were drought events in the 18 th century, and years 1822, 1844, 1846, 1859, 1886 were drought events in the 19 th century. The higher frequency of low growth events in the 18 th century than that in the 19 th and 20 th century closely matches other reconstructed drought events in California. Future inclusion of more species from the study area will help better constrain the nature of past drought events and help predict future drought events.