Hillslope-Channel Runoff Connectivity During the North American Monsoon in an Arid Piedmont Watershed

Zachary T. Keller and Enrique R. Vivoni

Arizona State University

Populations residing in arid regions depend heavily on limited amounts of groundwater that is often extracted at rates exceeding natural recharge. Arid aquifers are recharged primarily during flooding events that inundate channels and other permeable landscape features. In the southwestern United States, floods often occur during high intensity storms that are typical of the North American Monsoon during July, August, and September. In this study, we investigate runoff mechanisms leading to channel flooding in an instrumented mixed shrubland watershed of the Jornada Experimental Range, near Las Cruces, New Mexico. This works addresses the hillslope segment of the flood and recharge generation process through a set of runoff plots with varying amounts of Vegetated Space (VS) and interconnected Bare Space (BS). We present an analysis of nearly two years of data collected at four hillslope runoff plots and complemented by precipitation gauges, soil moisture sensors, channel runoff flumes, and evapotranspiration measurements. Varying amounts of VS and BS within north and south-facing plots was classified using an interactive supervised method. Through the analysis, we identify the effects varying amounts of BS and VS on hillslope processes and address the overarching hypothesis that increases in interconnected BS promotes runoff generation. Results indicate differences amongst plots with respect to water balance partitioning, runoff event counts, and discharge magnitude. North-facing plots show an increased response in runoff to precipitation events as do plots with greater amounts of BS. Seasonal analyses of maximum infiltration depth during precipitation events show a strong control on runoff generation. Improved understanding of the effects of hillslope connectivity on runoff generation is important for process-based hydrologic modeling and can inform water management of groundwater resources in arid regions.