Jeffrey S. Deems

Response of Colorado River runoff to dust radiative forcing in snow

The waters of the Colorado River serve 27 million people in seven states and two countries but are overallocated by more than 10% of the river’s historical mean. Climate models project runoff losses of 7–20% from the basin in this century due to human-induced climate change. Recent work has shown however that by the late 1800s, decades prior to allocation of the river’s runoff in the 1920s, a fivefold increase in dust loading from anthropogenically disturbed soils in the southwest United States was already decreasing snow albedo and shortening the duration of snow cover by several weeks. The degree to which this increase in radiative forcing by dust in snow has affected timing and magnitude of runoff from the Upper Colorado River Basin (UCRB) is unknown. Here we use the Variable Infiltration Capacity model with postdisturbance and predisturbance impacts of dust on albedo to estimate the impact on runoff from the UCRB across 1916–2003. We find that peak runoff at Lees Ferry, Arizona has occurred on average 3 wk earlier under heavier dust loading and that increases in evapotranspiration from earlier exposure of vegetation and soils decreases annual runoff by more than 1.0 billion cubic meters or ∼5% of the annual average. The potential to reduce dust loading through surface stabilization in the deserts and restore more persistent snow cover, slow runoff, and increase water resources in the UCRB may represent an important mitigation opportunity to reduce system management tensions and regional impacts of climate change.

Variation in Rising Limb of Colorado River Snowmelt Runoff Hydrograph Controlled by Dust Radiative Forcing in Snow

Author(s): Painter, TH; Skiles, SMK; Deems, JS; Brandt, WT; Dozier, J | Abstract: ©2017. American Geophysical Union. All Rights Reserved. Common practice and conventional wisdom hold that fluctuations in air temperature control interannual variability in snowmelt and subsequent river runoff. However, recent observations in the Upper Colorado River Basin confirm that net solar radiation and by extension radiative forcing by dust deposited on snow cover exerts the primary forcing on snowmelt. We show that the variation in the shape of the rising limb of the annual hydrograph is controlled by variability in dust radiative forcing and surprisingly is independent of variations in winter and spring air temperatures. These observations suggest that hydroclimatic modeling must be improved to account for aerosol forcings of the water cycle. Anthropogenic climate change will likely reduce total snow accumulations and cause snowmelt runoff to occur earlier. However, dust radiative forcing of snowmelt is likely consuming important adaptive capacity that would allow human and natural systems to be more resilient to changing hydroclimatic conditions.

Mapping snow-depth using KA-band InSAR: Calibration and validation during SnowEx

This paper discusses the evaluation of a state-of-the-art Ka-band (35.7GHz) single-pass interferometric synthetic aperture radar (InSAR) for snow-depth mapping during the NASA SnowEx experiment. The use of InSAR for this application presents a new approach and potential alternate technology to lidar with the advantage of wide-swath operation that is not hampered by cloud cover. We discuss the plans to leverage SnowEx for calibration, in particular characterizing potential biases due to interferometric penetration into the snow-cover by comparison with lidar and in situ measurements. In addition, lidar from the Airborne Snow Observatory will be used for validation of tree classifications and the derived digital surface models and snow-depth maps.