Urbanization alters watershed hydrology in the Piedmont of North Carolina

Abstract

The ecohydrologic effects of urbanization that is dominated by forests clearing are not well understood in the southeastern United States. We utilized long-term monitoring data to quantify the annual water balance, stormflow characteristics, and seasonal flow patterns of an urbanized watershed (UR) (0Ð70 km 2 ) and compared it to a fully forested watershed (FOR) (2Ð95 km 2 ) in central North Carolina. The goal of this study was to assess how past urbanization altered watershed hydrology and to offer reference data for urban watershed planning. The mean annual discharge coefficient (discharge/precipitation) in the UR and FOR from 2000 to 2007 was 0Ð42 and 0Ð24, respectively. The UR generated about 75% more stormflow than the FOR. The UR had a lower mean evapotranspiration (ET) rate (58%) than the FOR (77%). Peakflow rates and stormflow volume of the UR were higher (e.g. 76Ð6 mm/day versus 5Ð8 mm/day for peakflow rate and 77Ð9 mm/day versus 7Ð1 mm/day for stormflow volume) than the FOR, especially during the growing season. Growing season precipitation minus discharge normalized by precipitation (P Q)/P (i.e. normalized ET š change in water storage) was higher in the FOR compared to the UR. Differences between the two watersheds occurred mostly during the growing season and became smaller during the dormant season. We conclude that intensive urbanization elevated watershed peakflow rates and annual discharge volumes partially due to reduction in ET during the growing season. Maintaining ET capacity of vegetation in an urbanizing watershed is important in development planning for reducing stormflow and watershed degradation. Published 2011. This article is a US Government work and is in the public domain in the USA.

Hydrological Effects of Vegetation Cover Degradation and Environmental Implications in a Semiarid Temperate Steppe, China

“…The maximum slope of double mass curve and biggest runoff coefficient (Q/P = 0.021) in the 1990s with the most serious grassland degradation situation [21,23] (Figure 5) also supports our simulation results. Boggs and Sun [36] conclude that the effects of vegetation removal on streamflow are most pronounced during the growing seasons. Our results also showed that the reductions in vegetation cover can elevate the streamflow in both rainfall season (July-August) and the snowmelt season (March-April), but the effects of the former appear more obvious due to more vegetation cover in the rainfall season.…”

Urbanization dramatically altered the water balances of a paddy field-dominated basin in southern China

“…1). Thus, converting wetlands, such as paddy fields, to impervious or built-up areas is expected to have a much higher magnitude of hydrologic impacts than for converting dry croplands or forests to urban land uses (Tsai, 2002;Boggs and Sun, 2011). The ET estimates based on two independent methods, watershed water balance and remote sensing, all showed large decreases in ET.…”

“…Other studies have shown that reductions in forest land coverage, thus reduction in ET, could increase base flow in the humid piedmont region in North Carolina (Boggs and Sun, 2011) and northeastern US (Lull and Sopper, 1969). Boggs and Sun (2011) conclude that the effects of vegetation removal on stream flow are most pronounced during the growing seasons when the contrast between ET from a vegetated surface and from an urbanized surface is the highest. Therefore, it is plausible that replacing paddy fields with high ET with urban land uses (e.g., lawns or impermeable surfaces) with low ET may result in similar effects as forest removal during urbanization.…”

“…However, the hydrologic response to urbanization is extremely variable (Jacobson, 2011;Caldwell et al, 2012), due to climatic differences and land-use change patterns across a watershed (Sun and Lockaby, 2012). Empirical data are still lacking information about changes in water balances and watershed hydrologic characteristics other than storm flow, such as total flow, low flow, and evapotranspiration (ET) (Dow and DeWalle, 2000;Boggs and Sun, 2011) in different physiographic settings (Barron et al, 2013). Previous studies rely heavily on simulation models (Kang et al, 1998;Kim et al, 2005Kim et al, , 2014Sakaguchi et al, 2014).…”

Forest ecohydrological processes in a changing environment

“…Boggs and Sun (2011) studied the impacts of urbanization on hydrology through comparing an urbanized watershed (0Ð70 km 2 ) with a fully forested watershed (2Ð95 km 2 ) in Central North Carolina. Their study found that urbanization generated about 75% more streamflow and higher peak flows than those in the forested watershed, mainly due to differences in growing season ET rates between the two contrasting watersheds.…”