Surface runoff response to long-term land use changes: Spatial rearrangement of runoff-generating areas reveals a shift in flash flood drivers

Nowadays, rapid growths of urban areas and associated land use/land cover (LULC) changes notably affect the surface runoff response to rainfall in urbanised catchments. This effect of urbanisation on surface runoff is frequently ad-dressed since it relates to the increasing incidence of pluvial floods worldwide. Studies on this issue commonly assess runoff changes over several most recent decades. However, human-induced factors likely resulted in increased surface runoff and associated flash floods in rural catchments even in the past centuries. Such long-term changes have been rarely studied and thus are not well documented. This paper aims to fill this gap and assess the surface runoff response to LULC changes in a small catchment in southwestern Slovakia over more than two centuries. To meet this goal, we applied the Soil Conservation Service Curve Number (SCS-CN) method. We mapped past (1784) and present (2018) LULC classes based on historical maps and modern remote sensing data. Then, we estimated surface runoff depths for specific design rainstorms for both periods by executing CN method equations in the ArcGIS environment. Results revealed significant changes in surface runoff conditions between evaluated periods. In total, surface runoff magni-tudes increased by-230 and -130% for 40-and 65-mm design rainstorms, respectively, compared to 1784. More -over, surface runoff values show different spatial patterns on historical and present-day output raster images revealing spatial redistribution of runoff-enhancing and runoff-preventing areas during the evaluated period. Although both infiltration-enhancing and runoff-enhancing effects of LULC changes were identified, the latter effect associated with urbanised lowland areas was recognised as prevailing at present. In contrast, runoff-promoting conditions were associated with hilly vineyard areas in the past. These findings likely have important implications for understanding the past and present LULC-based controls of surface runoff generation and flash floods initiation.

Automated summary

The rapid growth of urban areas and associated land use/land cover changes have significantly affected the surface runoff response in urban catchments, leading to an increase in pluvial floods worldwide. While studies on runoff changes in recent decades are common, the long-term changes in surface runoff in rural catchments have been rarely studied and documented. This paper fills this gap by assessing the surface runoff response to land use/land cover changes in a small catchment in southwestern Slovakia over more than two centuries. The results reveal significant changes in surface runoff conditions, with a predominant increase in surface runoff in urbanized lowland areas.