Long‐Term Hydroclimatic Patterns in the Truckee‐Carson Basin of the Eastern Sierra Nevada, USA

Abstract

AbstractThe Truckee/Carson Basin, like other semiarid basins in the western United States, faces challenges to water management and planning under a changing climate. We analyzed tree‐ring data, along with instrumental climatic and hydrologic records, to provide a perspective on extreme drought in the 21st century. Drought indices highlighted a recent increase in the average duration of hydroclimatic episodes: in the new millennium average duration was 74% longer for the 24‐month Standardized Precipitation Index (SPI‐24) and 62% longer for the Palmer Drought Severity Index (PDSI) than in the previous century. Average snow water equivalent (SWE) declined 7% per decade from 1965 to 2018. The 2012‐2015 drought, in particular, stood out for its intensity and expression in snowpack, streamflow, and drought indices. Likely because of recent warming, this 4‐year drought event had a very low likelihood based on observed Carson River flows from the first half of the 20th century. A 501‐year tree‐ring reconstruction (1500‐2000 CE) of average water‐year streamflow for the Carson River indicated that positive (wet) spells had slightly longer duration (mean of 2.7 years and range from 1 to 10 years) than negative (dry) intervals (mean of 2.4 years and range from 1 to 9 years). The early 1900s pluvial, that is, 1905‐1911 in this record, was the third strongest episode in the entire reconstruction. The driest years were 1580 and 1934, both well‐known widespread and severe droughts in the western United States. Noise‐added reconstructions suggest that 2012‐2015, while not unique in the 401 years prior to the start of the Carson River gaged flows in 1901, was a less than one‐in‐a‐century event.