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Why It Matters:

Water managers and water scientists need accurate and timely information about rainfall to understand and model extreme weather events including floods and drought. In California, weather can be wildly diverse from one location to the next and from year to year. Most precipitation falls in the northern part of the state during the winter months, while most of the demand is in the southern part of the state, in the summer months. Flood forecasting, estimates of drought status, and water management, depend heavily on the availability of good-quality precipitation estimates. Difficulties in estimating precipitation can arise due to sparse ground-based measurement networks (rain gauges or weather radar).

How NASA Contributes:

Remote-sensed precipitation data can be used to complement rain gauge data throughout the state and to fill in gaps in the relatively sparse network of gages. These data are spatially consistent and provide homogeneous quality of measurements over broad regions.  Improved estimates of precipitation throughout the state can be used to improve rainfall-runoff models, forecasts of water availability and could be useful for farmers who grow rain-fed (non-irrigated) crops.

NASA Missions that help monitor precipitation: The Tropical Rainfall Measurement Mission (TRMM) and the Global Precipitation Monitor (GPM).


Why It Matters:

Much of California's water supply is stored as snow in the Sierra Nevada, with snowmelt runoff supplying about 75 percent of the agricultural water used in the Central Valley. Having an accurate read on snowpack volume is vitally important to water managers responsible for making allocation decisions and forecasts

How NASA Contributes:

NASA remote sensing observations of snowpack by elevation can augment current ground monitoring data. These data could be incorporated into runoff forecast models to improve estimates of water supply availability and could be used to estimate snow water equivalent (and hence runoff) for the Sierra Nevada.

NASA Missions that help monitor snowpack: MODIS and the Airborne Snow Observatory


Why It Matters:

Recent California legislation calls for improving the state's ability to monitor groundwater supplies. This is a massive task in light of California's geographic extent, high usage of groundwater, and limited budgetary resources. Many local agencies measure their own groundwater resources in situ and collect from others on a voluntary basis, For high-priority small areas, a local sensor network can suffice for monitoring the groundwater if the area is accessible. For large areas, in situ measurements and subsequent analysis are labor-intensive, time-consuming, and have large spatial gaps in the data sets. 

Subsidence in CA Central Valley

How NASA Contributes:

Spatially consistent monitoring for large areas, such as the Central and Salinas Valleys, at a minimum frequency of twice a year is highly desirable for groundwater management and decision-making. Groundwater information products based on radar measurements can be used to complement studies of the impacts of climate, drought, flood, water use, and water management activities on groundwater condition. The unique benefit of NASA remote sensing in this application is the ability to provide qualitative coverage of large spatial regions relatively inexpensively. 

Left: Surface deformation caused by overdraft of groundwater in California’s Central Valley was mapped using Japan’s PALSAR. Well measurements within the large subsidence bowl show subsidence of about 35 cm between 2007 and 2010 while the water level decline is from 202 to 198 feet due to several dry or average years (red and black). Above-normal precipitation in 2011 ( blue) brought water levels up to earlier values, but the ground surface responds more slowly. Deformation of the surface has resulted in the need for repairs to the California Aqueduct. The original siting of the California High Speed Rail was discovered to be directly through the large subsidence bowl.


NASA Missions that help monitor groundwater and subsidence related to groundwater: The Gravity and Climate Experiment Mission GRACE and the GRACE Follow-on Mission GRACE-FO, the NASA-ISRO SAR Mission (NISAR) (scheduled for launch in 2021), and a NASA airborne mission - UAVSAR

Soil Moisture

Why It Matters:

Soil moisture strongly affects plant growth and hence agricultural productivity, especially during conditions of water shortage and drought. Long-term observations and retrospective simulations of soil moisture and evapotranspiration for natural and managed landscapes would provide value in consumption mapping and calculating regional water budgets.

How NASA Contributes:

Data from NASA satellites can provide spatially consistent remote sensing products, including soil moisture data, that can be used to derive both potential and actual evapotranspiration. Estimates of evapotranspiration can serve as inputs to operational processes to determine water releases required to meet irrigation demands. The availability of direct observations of soil moisture will also help to enable improvements in operational crop productivity and water stress information systems by providing realistic soil moisture observations as inputs for agricultural prediction models.

NASA Missions that help monitor soil moisture: The Advanced Microwaved Scanning Radiomenter (AMSR-E) (no longer operational, but a 10 year historic record), the Soil Moisture Active Passive Mission (SMAP), and the Ariborne Passive Active L-Band Sensor (PALS)