Abstract
Runoff signatures, including low flow, high flow, mean flow and flow variability, have important implications on the environment and society, predominantly through drought, flooding and water resources. Yet, the response of runoff signatures has not been previously investigated at the global scale, and the influencing mechanisms are largely unclear. Hence, this study makes a global assessment of runoff signature responses to the El Nino and La Nina phases using daily streamflow observations from 8217 gauging stations during 1960-2015. Based on the Granger causality test, we found that similar to 15% of the hydrological stations of multiple runoff signatures show a significant causal relationship with El Nino-southern oscillation (ENSO). The quantiles of all runoff signatures were larger during the El Nino phase than during the La Nina phase, implying that the entire flow distribution tends to shift upward during El Nino and downward during La Nina. In addition, El Nino has different effects on low and high flows: it tends to increase the low and mean flow signatures but reduces the high flow and flow variability signatures. In contrast, La Nina generally reduces all runoff signatures. We highlight that the impacts of ENSO on streamflow signatures are manifested by its effects on precipitation (P), potential evaporation (PET) and leaf area index (LAI) through ENSO-induced atmospheric circulation changes. Overall, our study provides a comprehensive picture of runoff signature responses to ENSO, with valuable insights for water resources management and flood and drought disaster mitigation.