Impacts of water regulation through a reservoir on drought dynamics and propagation in the Pilica River watershed

Tesfaye B. Senbeta, Jarosław Napiórkowski, Emilia Karamuz, Krzysztof Kochanek, Yali E. Woyessa

Study region: The Pilica River watershed, located in central Poland, is the largest left tributary of the Vistula River basin. Study focus: The study aims to assess the impact of human activities on drought dynamics by considering the specific role of the Sulej´ow Reservoir. Identifying factors contributing to drought development is essential for decision-makers to implement appropriate management measures. The temporal overlap method is used to distinguish between climate and human-driven droughts. The changes in drought propagation are assessed using the time shift method at various accu- mulation time scales. To assess the spatial distribution of drought, we applied the Soil and Water Assessment Tool (SWAT) model to simulate soil moisture and streamflow response at a spatial scale. New hydrological insights for the region: The findings highlight that about 75% of meteorological droughts lead to soil moisture droughts, and about 70% result in hydrological droughts. The results show the contribution of human activities to soil moisture drought (~25%) and hydro- logical drought (~10%), indicating that not all droughts are driven by meteorological factors alone. The key finding suggests a shorter and longer time scale of around 3 and 12 months for soil moisture drought and hydrological drought propagation analysis, respectively. Moreover, the decrease in the duration and severity of drought during 2005–2019 compared to 1997–2004 suggests that the magnitude of the reservoir impact depends on its purpose and operational strategies.

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