Precipitation patterns across the Marañón basin. (A) Mean precipitation calculated for major subbasins across the upper Marañón basin show a drier trend at higher elevations (southeastern region of the basin) year round as compared to lower-lying watersheds. This geographic behavior is accentuated during the dry season as demonstrated by average precipitation values calculated across watersheds for July (right dashed vertical line) in (B) major subbasins and (C) sampled subbasins. Line colors in (A) match basin colors in (B). In (C) white areas represent tributary watersheds of the upper Marañón basin that were not sampled. DOI: https://doi.org/10.1525/elementa.290.f4