Derivation of Interannual Climate Elasticity of Streamflow

Besides climate change (i.e., change on an average condition), streamflow change is also affected by interannual variability of climate (i.e., change from year to year). To quantify the impact of interannual climatic variability, in this study, we first clarify the content and definition of interannual climate elasticity that represents the sensitivity of streamflow to climatic variability from year to year and equals to the ratio of proportional annual change in streamflow and a climatic variable. Then, we analytically derive the interannual climate (i.e., potential evapotranspiration and precipitation) elasticities of streamflow by integrating the annual water balance with a conceptual hydrologic model (i.e., extended Budyko framework). At interannual scale, the terrestrial water storage change (i.e., ∆S) is a substantial component of water balance equation. Consequently, the analytical solutions of the interannual climate elasticities are functions of precipitation, potential evapotranspiration, and ∆S. The newly derived interannual climate elasticities are applied to 335 Model Parameter Estimation Experiment watersheds as a case study to evaluate the hypotheses in this study and construct the regional map of the streamflow sensitivity to interannual variability of climate. Results show that the interannual precipitation elasticity is generally larger than the absolute interannual potential evapotranspiration elasticity across study watersheds. Spatially, streamflow in the arid region tends to be more sensitive to interannual variability of climate than that in humid region. This study may be useful for understanding the extreme events and annual streamflow change caused by the ∆S(e.g., groundwater abstraction) across watersheds or regions. The analytical solutions of interannual climate elasticities of streamflow are derivedThe influence of terrestrial water storage change is integrated in the derivation of the interannual climate elasticitiesThe regional map of streamflow sensitivity to interannual climatic variability across the United States is provided