From Mountains to Deserts: Changes in Snow and Flood Intensity and Intermittence

Dr. Adrienne Marshall, Ph.D., assistant professor Geology and Geological Engineering Department, Colorado School of Mines, and Dr. Efrat Morin, Ph.D., professor, Institute of Earth Sciences, Hebrew University of Jerusalem will discuss changes in snow and flood intensity and intermittence across the world.

Dr. Adrienne Marshall, Ph.D., assistant professor Geology and Geological Engineering Department, Colorado School of Mines

Abstract: Declining snowfall in mountainous regions is a major consequence of climate change that impacts snowpack and ultimately streamflow timing and magnitude. In the western U.S., declining average snowfall is well established, but changes in snowfall intensity and snow intermittence are less well understood yet have significant consequences for terrestrial hydrology, snow-dependent ecosystems, and streamflow. For instance, changing snowfall intensity can alter the snow energy balance, altering mid-winter melt. Intermittence of the snowpack can impact soil temperature and moisture dynamics, but the impacts of climate change on snow intermittence are complex: for instance, warmer temperatures could increase ablation events that increase intermittence, but could also reduce the probability of shoulder season snowfall events, when intermittence is most likely. This talk describes the impacts of changing snowfall intensity on mid-winter melt in historical and projected future climates, the climatic factors that contribute to snow intermittence, and observed changes in snow intermittence.   

Biography: Dr. Adrienne Marshall is a computational hydrologist who uses process-based modeling and data science approaches to study climate change impacts on snow, ecohydrology, permafrost, and hydropower. Her research interests are united by a desire to understand how climate change is altering water resources, and solutions to these problems from both adaptation and mitigation perspectives. Dr. Marshall is an Assistant Professor in the Geology and Geological Engineering Department with an affiliation with the Hydrologic Sciences and Engineering program at the Colorado School of Mines. She holds a doctorate in water resources from the University of Idaho, an master’s degree in energy and resources from U.C. Berkeley, and a bachelor’s degree in biology from Scripps College.

Dr. Efrat Morin, Ph.D., professor, Institute of Earth Sciences, Hebrew University of Jerusalem

Abstract: More than a quarter of the earth's land area is under an arid climate regime, and the population size in such regions is steadily increasing. Rainfall in arid areas is scarce and meager, but rain intensities can be high. Falling on bare soil or exposed rock surfaces, covered by only sparse vegetation, runoff generation is fast and may lead to large flash floods. In this presentation, we discuss flash flood characteristics and hydrometeorological processes in an arid environment, demonstrated in the region of the Eastern Mediterranean. Rainfall, as the major forcing, is first considered. We show that although storm rain depth is much lower in arid areas than in more humid regions, local rain intensities of short durations and long recurrence intervals are typically higher. Rainstorms are often composed of convective rain cells of only a few km radii and a short life span. We present a climatological analysis of space-time properties of convective rain cells in arid areas derived from a long, high-resolution radar rainfall data record. Next, the sensitivity of flash flood magnitude to rainfall properties is considered. In arid regions, this sensitivity is amplified due to the relatively minor role of antecedent conditions and soil moisture content, and the primary role of rain intensities, for flash flood generation. In fact, large flash floods can be produced by a single convective rain cell. We present the dependency of flash flood magnitude on rain cell properties such as intensity, area, location, direction, and speed, both from a statistical point of view and using hydrological models. In the last part, we discuss how the above unique relationships are manifested in flash flood characteristics. Specifically, we consider flood peak discharge and envelop curves, hydrograph shapes, lag times, runoff to rainfall ratios, and more. We also discuss the effect of catchment size on flash flood magnitude, considering rainstorm size and the additional impact of transmission losses that can be dominant in arid catchments.

Biography: Dr. Efrat Morin is a professor at the Institute of Earth Sciences of the Hebrew University of Jerusalem, Israel. She has all her degrees from the Hebrew University, and her post-doc was at the Department of Hydrology and Water Resources at the University of Arizona. Her research focuses on understanding, modeling, and predicting dominant processes and interactions of hydrological and meteorological systems at different space-time scales. In particular, she is interested in space-time patterns of precipitation fields and how these are related to meteorological controls on the one hand and hydrological impacts on the other.

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