California legislation calls for improving the state's ability to monitor groundwater. 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.
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 of land subsidence 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.
Much of the state'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.
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.
SOIL MOISTURE & EVAPOTRANSPIRATION
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.
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.
With a population expected to more than double by 2050 and a limited supply of fresh water, the protection of water for both human uses and environmental resource protection is of vital concern. There is a need to increase the amount of usable, quantitative data and information to support monitoring and assessment of the state's water.
Advances in water quality research using remotely sensed estimates of water quality parameters could help to facilitate and augment estuarine monitoring. Two areas where NASA research and observations can provide benefit are assessment of spatial patterns of water temperature and estimation of water quality parameters such as suspended sediments, turbidity, and chlorophyll. Such data can be used to derive estimates of water quality parameters to provide a consistent view of the delta region as a whole.
The Sacramento–San Joaquin Delta is the state's most important water resource, and also the most fragile. The Delta comprises levee-protected islands that were formed beginning in the late 1800s when freshwater marshland was drained for agriculture. Since then, the islands have been sinking, with most of them currently below sea level. Now there are over 1100 miles of levees in the Delta, many constructed using outdated engineering methods and all subject to pressure from island subsidence (sinking) and possible failure resulting from a major earthquake. A levee failure would lead to flooding and contamination of the water supply, potentially causing catastrophic loss of fresh water for much of California.
NASA aircraft radar can be used to monitor island subsidence spanning the entire Delta in a single data collection. Monthly measurements can provide ongoing information about the integrity of the levees, and multiyear data sets can provide information about long-term subsidence trends within individual islands.
California water managers are required to forecast water availability over a range of time scales extending out to decades. Reliance on traditional methods has become problematic due to the challenges of incorporating the effects of climate change into resource forecasts. Moreover, water agencies typically lack funding for developing and exploring the use of regional climate models to downscale global climate model projections.
NASA modeling expertise, computer infrastructure, and observations are well suited to design and apply model-observation comparison frameworks to help develop and evaluate climate models that water planners need to make assessments and forecasts.