Predicting the river's blue line for fish conservation.

Abstract

River drying is increasing in frequency, duration, and extent in the United States, especially across the Sunbelt where drought has become the new norm (Fig. 1). Exceptional droughts and climate change are one cause of drying—surface water is scarcer and that trend is not changing (1⇓⇓–4). Increasing human appropriation of groundwater—especially during drought—is another cause (5, 6). River drying has clear implications for freshwater biodiversity, including mass mortality of commercially important fish if large reaches of a river dry completely (7). A much more subtle, but equally detrimental, impact of drying is habitat fragmentation, which can increase the risk of extinction from other causes (8, 9); however, data availability and a methodological void have left this critical issue unaddressed until now. In PNAS, Jaeger et al. (10) fill this void by integrating cutting edge and empirically grounded ecology with a tried-and-true surface water model that is in turn forced with forecasted and downscaled climate data. The authors use this intriguing model mashup to forecast network connectivity of flowing reaches in a desert river in Arizona at fine spatial scales. They then use this set of “blue lines” to forecast the persistence of the river's native fish populations. Their conclusions are dire: decreasing persistence of an endemic fauna. On the bright side, the mashup has real potential to be applied to address similar management problems in other basins. Fig. 1. ( Upper ) Mean (solid) and 95% CI (dashed) number of zero flow days for 23 stream gages across the US Sunbelt from the USGS National Water Information System (NWIS). Data cover a spatial extent that includes the states of Georgia, Florida, Kansas, Texas, New Mexico, and Arizona. ( Lower ) Mean (solid) and CI (dashed) number of days (per year) below the 40-y average (dotted black reference line) for 94 … [↵][1]1Email: john.l.sabo{at}asu.edu. [1]: #xref-corresp-1-1