Snow Cover Monitoring from Remote-Sensing Satellites : Possibilities for Drought Assessment

Snow cover is an important earth surface characteristic because it inžuences partitioning of the surface radiation, energy, and hydrologic budgets. Snow is also an important source of moisture for agricultural crops and water supply in many higher latitude or mountainous areas. For instance, snowmelt provides approximately 50%–80% of the annual runoff in the western United States (Pagano and Garen, 2006) and Canadian Prairies (Gray et al., 1989; Fang and Pomeroy, 2007), which 15.1 Introduction .................................................................................................. 359 15.2 Snow Mapping with Optical Satellite Observations ..................................... 361 15.2.1 Physical Principles and Sensor Characteristics ................................ 361 15.2.2 Primary Optical-Based Products ...................................................... 363 15.2.3 Validation of Optical Products ......................................................... 365 15.3 Snow Mapping with Microwave Satellite Observations ...............................366 15.3.1 Physical Principles and Instrument Characteristics .........................366 15.3.2 Primary Microwave-Based Products ................................................ 369 15.3.3 Validation of Microwave Products ................................................... 371 15.3.4 Data Assimilation Approaches for Estimating Snow Water Equivalent............................................................................... 372 15.4 Snow Cover Monitoring Using Synergy of Optical and Microwave Remote-Sensing Techniques ......................................................................... 374 15.5 Application of Satellite-Based Snow Products for Drought Identi–cation and Monitoring ....................................................................... 375 15.6 Conclusions ................................................................................................... 382 References .............................................................................................................. 383 substantially impacts warm season hydrology. Limited soil moisture reserves from the winter period can result in agricultural drought (i.e., severe early growing season vegetation stress if rainfall de–cits occur during that period), which can be prolonged or intensi–ed well into the growing season if relatively dry conditions persist. Snow cover de–cits can also result in hydrological drought (i.e., severe de–cits in surface and subsurface water reserves including soil moisture, streamžow, reservoir and lake levels, and groundwater) since snowmelt runoff is the primary source of moisture to recharge these reserves for a wide range of agricultural, commercial, ecological, and municipal purposes. Semiarid regions that rely on snowmelt are especially vulnerable to winter moisture shortfalls since these areas are more likely to experience frequent droughts. In the Canadian Prairies, more than half the years of three decades (1910-1920, 1930-1939, and 1980-1989) were in drought. Wheaton et al. (2005) reported exceptionally low precipitation and low snow cover in the winter of 2000-2001, with the greatest anomalies of precipitation in Alberta and western Saskatchewan along with near-normal temperature in most of southern Canada. The reduced snowfall led to lower snow accumulation. A loss in agricultural production over Canada by an estimated $3.6 billion in 2001-2002 was attributed to this drought. Fang and Pomeroy (2008) analyzed the impacts of the most recent and severe drought of 1999/2004-2005 for part of the Canadian Prairies on the water supply of a wetland basin by using a physically based cold region hydrologic modeling system. Simulation results showed that much lower winter precipitation, less snow accumulation, and shorter snow cover duration were associated with much lower discharge from snowmelt runoff to the wetland area during much of the drought period of 1999/2004-2005 than during the nondrought period of 2005/2006.

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