Impact of forecasted land use changes on flood risk in the Polish Carpathians

Nat Hazards https://doi.org/10.1007/s11069-018-3384-y ORIGINAL PAPER Impact of forecasted land use changes on flood risk in the Polish Carpathians Marcin Szwagrzyk1 • Dominik Kaim1 • Bronwyn Price2 • Agnieszka Wypych1 • Ewa Grabska1 • Jacek Kozak1 Received: 7 April 2017 / Accepted: 22 May 2018 Ó The Author(s) 2018 Abstract Flooding is a major environmental hazard in Poland with risks that are likely to increase in the future. Land use and land cover (LULC) have a strong influencing on flood risk. In the Polish Carpathians, the two main projected land use change processes are forest expansion and urbanization. These processes have a contradictory impact on flood risk, which makes the future impact of LULC changes on flooding in the Carpathians hard to estimate. In this paper, we investigate the impact of the projected LULC changes on future flood risk in the Polish Carpathians for the test area of Ropa river basin. We used three models of spatially explicit future LULC scenarios for the year 2060. We conduct hydrological simulations for the current state and for the three projected land use scenarios (trend extrapolation, ‘liberalization’ and ‘self-sufficiency’). In addition, we calculated the amount of flood-related monetary losses, based on the current flood plain area and both actual and projected land use maps under each of the three scenarios. The results show that in the Ropa river, depending on scenario, either peak discharge decreases due to the forest expansion or the peak discharge remains constant—the impact of LULC changes on the hydrology of such mountainous basins is relatively low. However, the peak discharges are very diverse across sub-catchments within the modeling area. Despite the overall decrease of peak discharge, there are areas of flow increase and there is a substantial projected increase in flood-related monetary losses within the already flood-prone areas, related to the projected degree of urbanization. Keywords LULC
LU modeling
Flood risk assessment
SCS CN
Carpathians Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11069-0183384-y) contains supplementary material, which is available to authorized users. & Marcin Szwagrzyk 1 Institute of Geography and Spatial Management, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland 2 Landscape Dynamics Unit, Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland 123 Nat Hazards 1 Introduction Flood risk is defined as a combination of the probability of a flood event and its negative consequences (UNISDR 2009). Flood risk is considered to be increasing at global and local scales (Kundzewicz et al. 2010) due to climate change and other processes such as the increase of urban area in flood-prone zones (European Parliament 2007; Kundzewicz et al. 2016; Matczak et al. 2017). Riverine flooding is the biggest natural hazard in Poland (Matczak et al. 2016). In the Polish Carpathians, the most frequent and the most dangerous riverine floods are those caused by rainfall events which last for multiple days in a row, which occur mainly in June and July (Bryndal 2015; Wy_zga et al. 2016). Land use and land cover (LULC) affects both the probability of flood and its consequences in several ways. Land cover affects different elements of the water balance—i.e., evaporation, ground temperatures and interception (Stonestrom et al. 2009). In addition, LULC impacts climate systems, and, in turn, the frequency and characteristics of rainfall (Cornelissen et al. 2013; Boysen et al. 2014; Mitsova 2014). Moreover, there is a direct impact of LULC on the formation of runoff from a particular rainfall event (Tellman et al. 2015). Finally, the land cover in river channels affects the conditions of hydraulic flow and contributes to, for example, woody debris jams on bridges (Stoffel et al. 2016). LULC changes have implications for the consequence component of flood risk through increased development of settlements on flood-prone areas (Kundzewicz et al. 2010). Numerous studies have considered the general impact of land use change on flooding; however, there are fewer studies of the projected (simulated) impact of future land use on flood risk. Current studies often focus on the impact of forecasted land use on flood consequences, particularly damage in urbanized areas (Chen and Yu 1999; Huong and Pathirana 2013; Mitsova 2014; Choi et al. 2016). Depending on the features of the studied areas and modeled LULC changes, the results were usually similar: urbanization in flood-prone areas causes rapid increase of the projected flood damage. A few studies consider the impact of the projected land cover changes on hydrology and find this impact not significant or even negligible (Altarejos-Garcia et al. 2012; Choi et al. 2016), especially in comparison to other factors such as climate change. In other cases, the projected LULC changes (i.e., urbanization) were shown to cause an increase in peak discharge (Huong and Pathirana 2013; Mitsova 2014). Notably, all the above studies were conducted in urbanized catchments, where further urbanization was the main projected LULC process. So far, less attention has been paid to future flood risk in basins where the main projected LULC processes are related to the transformation of agricultural land uses, e.g., reforestation or urban sprawl. Poland continues to experience rapid economic and social transitions that affect land use changes (Jepsen et al. 2015) and thereby flood risk. In the mountainous areas of southern Poland, the two main LULC change processes are forest expansion and the development of built-up areas, which includes urban sprawl and the development of second homes (Kaim et al. 2016; Kaim 2017). Price et al. (2017) find that in the coming decades (until 2060) these processes will continue and influenced by past land use patterns, the spatial distribution of changes will diversify. Forecasted LULC change processes may have contradictory impacts on the formation of runoff. Forest expansion mitigates runoff (e.g., due to retention increase) while urbanization increases it (e.g., due to the increase of impervious areas) (Tellman et al. 2015). Therefore, it is impossible to determine the overall direction of changes in runoff without detailed complex computations. So far, there have been no such analyses for any areas in 123 Nat Hazards Poland, largely because spatially explicit complex future scenario modeling for large areas has been lacking to date. Currently, the level of the flood risk in Poland is evaluated by decision makers based on hydraulic and hydrological modeling and spatial analyses (IMGW 2013; Graf 2014). LULC maps are an input to this modeling and analysis. Decisions concerning spatial planning and flood protection means are made based on the flood risk assessment for the current state. These assessments determine flood protection actions, whose implementat (...truncated)