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Abstract We present a new, nearly half-millennium suite of annual atmospheric river (AR) reconstructions for northern, central and southern California (CA) (United States). The reconstructed variables encompass five indices of AR activity: landfall counts, integrated water vapor, integrated vapor transport and its associated zonal and meridional components. Thus, we include critical measures of AR moisture intensity and spatial delivery. We take advantage of the assimilation reconstruction methodology employed in several prior studies to evaluate winter circulation over the Pacific-North American sector and Pacific sea surface temperatures (SSTs) in relation to AR activity. These include consideration of recently raised questions, such as whether AR activity can reduce the strength of the teleconnection between the El Niño-Southern Oscillation (ENSO) and winter precipitation in CA. Our results align with those reported by Luna-Niño et al. (2025), indicating that AR activity interferes with the canonical ENSO teleconnection to California precipitation. Our reconstructions indicate substantial ongoing variability in the “canonical” and “heretical” link between ENSO and California precipitation, though generally without clear linkages to either ongoing (global warming) or episodic (e.g., large volcanic eruption) forcing. More generally, as suggested by previous studies, strong and persistent long-term forcing—for example, continuing anthropogenic or other external mechanisms—appears necessary to modify the longer-term association of AR activity and CA precipitation. Our results are consistent with the approximately white noise character of CA precipitation over the past half-millennium. Nevertheless, the variability of AR activity attains its highest values during the last decades of the record, suggesting that a second-moment response to anthropogenic forcing may be emerging.
Wahl et al. (Fri,) studied this question.