Evaluation of ENSO Impact on Hydroclimatic Variability

Primary author: Chen Xu
Co-author(s): Mingliang Liu; Jennifer Adam; John Abatzoglou; Kirti Rajagopalan
Faculty sponsor: Jennifer Adam, Kirti Rajagopalan

Primary college/unit: Voiland College of Engineering and Architecture
Campus: Pullman


Superposed epoch analysis is performed to 1) quantify the effects of ENSO phase on the distribution of hydroclimatologic anomalies across the PNW, and 2) identify where these anomalies are statistically significant. Annual and seasonal precipitation and temperature anomalies are analyzed using gridded observations from the gridMET product, while runoff, evapotranspiration and soil moisture anomalies are obtained through VIC-CropSyst simulations (a coupled macroscale hydrologic and cropping system model). Results reveal strong precipitation anomalies over the mountainous regions, although not with a consistent sign for all mountain ranges. El Niño (La Niña) years are drier (wetter) than normal over the North Cascades, Bitterroots, and Northern Rockies; while the opposite effect is experienced by the Olympic Mountains. Outside of mountainous areas, precipitation anomalies are smaller and heterogeneous but with generally more (less) rainfall during El Niño (La Niña) years. Runoff, evapotranspiration and soil moisture anomalies are found to be generally consistent with the precipitation anomalies. There are, however, limited variables and areas with statistically significant anomalies, including El Niño precipitation and runoff in northern Idaho, and La Niña evapotranspiration in western Washington. Given that the skill of seasonal forecasts (with lead time of 1 to 7 months) has been associated with the ENSO signal, this study has the potential to provide insights in building institutional decision support capacity through a forecast system. It helps such a system prioritize meteorological, hydrological and agriculture relevant variables with sufficient forecast skill in a region-specific manner, and inform agricultural and water resources decisions in a meaningful way.