Climate Elasticity of Annual Streamflow in Northwest Bulgaria

The study of hydrological response to long-term climate changes is a particularly significant problem and an important task for the applied hydrology. This topic is also a challenge for geography. There are many different methods and criteria for the determination of this hydro-climatic relationship. The aim of present work is to explore one of these approaches: climate elasticity of streamflow (\( \varepsilon_{p} \)). As a case region, the territory of seven catchment areas situated in Northwest Bulgaria was selected. Results obtained show relatively large variations of \( \varepsilon_{p} \)—it ranges from 0.526 to 1.404, thus a ten percent change in mean annual precipitation would be reflected within 5.26–14.04% change in mean annual flow. The calculations in this paper establish strong inverse correlations between \( \varepsilon_{p} \), runoff coefficient and mean annual streamflow (a coefficient of determination: R2 > 0.80), explained by the nonlinear “rainfall–runoff” relationships. There are also spatial variations of the \( \varepsilon_{p} \) value—it is lower in the upper streams and increases toward the mouths of the rivers. The assessment of climate elasticity of streamflow is an informative approach for an estimate of climate change impacts to hydrological systems and provides an opportunity for effective water resources management.