Relationship between Drought Characteristics and the Extent of Urban Land Cover: The Case of the Milwaukee River Basin in Wisconsin (USA)
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It is well known that land covers significantly influence hydrological processes, particularly in urban catchments. However, it is less well known how urban land covers affect hydrological (streamflow) drought. This study investigated how streamflow drought characteristics vary along with the extent of urban land cover and compared them to precipitation drought characteristics. The Milwaukee River basin was chosen as the study area to build on previous research related to streamflow characteristics and urban land cover. Three catchment areas (Cedarburg, Menomonee, and Kinnickinnic) that have different extents of urban land cover in the Milwaukee River basin were examined. Streamflow and precipitation droughts were diagnosed using the variable threshold level method and daily streamflow and precipitation data for the period 1983-2022. For streamflow drought, the maximum and mean durations were longest in the Cedarburg catchment, which is the least urbanized. On the other hand, they were shortest in the Kinnickinnic catchment, more than 98% of which is urban. The mean deficit relative to the mean annual runoff was largest in Cedarburg and smallest in Kinnickinnic. Not surprisingly, the characteristics of precipitation drought were very similar between the catchments. From this exploratory study, I speculate that highly urbanized catchments are likely to experience shorter but less intense streamflow droughts than less urbanized ones largely because of increased variability and magnitude of streamflow.
Abstract
It is well known that land covers significantly influence hydrological processes, particularly in urban catchments. However, it is less well known how urban land covers affect hydrological (streamflow) drought. This study investigated how streamflow drought characteristics vary along with the extent of urban land cover and compared them to precipitation drought characteristics. The Milwaukee River basin was chosen as the study area to build on previous research related to streamflow characteristics and urban land cover. Three catchment areas (Cedarburg, Menomonee, and Kinnickinnic) that have different extents of urban land cover in the Milwaukee River basin were examined. Streamflow and precipitation droughts were diagnosed using the variable threshold level method and daily streamflow and precipitation data for the period 1983-2022. For streamflow drought, the maximum and mean durations were longest in the Cedarburg catchment, which is the least urbanized. On the other hand, they were shortest in the Kinnickinnic catchment, more than 98% of which is urban. The mean deficit relative to the mean annual runoff was largest in Cedarburg and smallest in Kinnickinnic. Not surprisingly, the characteristics of precipitation drought were very similar between the catchments. From this exploratory study, I speculate that highly urbanized catchments are likely to experience shorter but less intense streamflow droughts than less urbanized ones largely because of increased variability and magnitude of streamflow.