Tree-ring footprint of joint hydrologic drought in Sacramento and Upper Colorado river basins, western USA

Growing and changing demands on water supply, along with natural climate variability and possible anthropogenically induced climate change, make water resource management and planning increasingly challenging, particularly in arid regions. Instrumental climate and gaged streamflow records provide just a snapshop of recent natural hydrologic variability. In this paper, we use tree-ring-based annual streamflow reconstructions for the Sacramento River in California and the Blue River in western Colorado to analyze the temporal and spatial variability of widespread drought simultaneously affecting both basins over the past five centuries. Stability of joint-drought episodes and the covariation of reconstructed flows in the two basins are analyzed with sliding correlations, spectral analysis and a hypergeometric test. Year-to-year spatial patterns of moisture anomalies in a singular joint-drought episode in the late-1500s are mapped with a network of tree-ring data. Climatological aspects of joint droughts of the 20th century are investigated with 500-mb geopotential height data and climatic indices.