The Impact of Rainfall Movement Direction on Urban Runoff Cannot Be Ignored in Urban Hydrologic Management

Urban floods have been exacerbated globally, associated with increasing spatial-temporal variations in rainfall. However, compared with rainfall variabilities of intensity and duration, the effect of rainfall movement direction is always ignored. Based on 1313 rainfall scenarios with different combinations of rainfall intensity and rainfall movement direction in the typically rainy city of Shenzhen in China, we find that the effect of rainfall movement direction on the peak runoff may reach up to 20%, which will decrease to less than 5% under heavy rainfall intensity conditions. In addition, our results show that the impact of rainfall movement direction is almost symmetrical and is associated with the direction of the river. The closer rainfall movement direction is to the Linear Directional Mean of rivers, the larger is the peak runoff of section. Our results reveal that rainfall movement direction is significant to urban peak runoff in the downstream reaches, which should be considered in urban hydrological analysis.

The impact of RMD on urban runoff cannot be ignored in urban hydrologic management

Urban floods have been exacerbated globally, associated with increasing spatial-temporal variations of rainfall. However, compared with rainfall variabilities of intensity and duration, the effect of RMD is always ignored. Based on 1313 rainfall scenarios with different combinations of rainfall intensity(RI) and RMD in a typical rainy city of Shenzhen in China, we investigate the urban runoff response in relation to RMD and the spatial feature of rivers. Our results show that the effect of RMD on the peak runoff may reach up to 20%, which will decrease to less than 5% under heavy RI conditions. In addition, we find that the impact of RMD is almost symmetrical and is associated with the direction of the river. The closer RMD is to the Linear Directional Mean of upstream, the larger peak runoff of section is. Our results reveal that RMD is significant to urban peak runoff in the downstream reaches, which should be considered in urban hydrologic model.

Short- and long-term hydrologic controls on smouldering fire in wetland soils

Smouldering fire vulnerability in organic-rich, wetland soils is regulated by hydrologic regimes over short (by antecedent wetness) and long (through influences on soil properties) timescales. An integrative understanding of these controls is needed to inform fire predictions and hydrologic management to reduce fire vulnerability. The Great Dismal Swamp, a drained peatland (Virginia and North Carolina, USA), recently experienced large wildfires, motivating hydrologic restoration efforts. To inform those efforts, we combined continuous water levels, soil properties, moisture holding capacity and smouldering probability at four sites along a hydrologic gradient. For each site, we estimated gravimetric soil moisture content associated with a 50% smouldering probability (soil moisture smoulder threshold) and the water tension required to create this moisture threshold (tension smoulder threshold). Soil properties influenced both thresholds. Soils with lower bulk density smouldered at higher moisture content but also had higher moisture holding capacity, indicating that higher tensions (e.g. deeper water tables) are required to reach smouldering thresholds. By combining thresholds with water level data, we assessed smouldering vulnerability over time, providing a framework to guide fire prediction and hydrologic restoration. This work is among the first to integrate soil moisture thresholds, moisture holding capacities and water level dynamics to explore spatiotemporal variation in smouldering fire vulnerability.