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Water

Water: Sustaining Life
NISAR will measure aquifer extent and change over the Earth's vulnerable water systems.
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Understanding Aquifers Dynamics for Managing Water Resources
Water is necessary for life, both for drinking and for growing food. In the more arid parts of the world rainfall and surface water can't satisfy the growing demands of the people who live in those regions. Groundwater makes up the difference, acting as a reservoir that can be tapped through wells. Unfortunately, climate change coupled with growing populations is causing increasing stress on groundwater resources around the world. Over-exploitation of groundwater leads to lowering of the water table and, in alluvial basins, compaction of the aquifer system leading to sinking of the land surface (subsidence). Subsidence is often the first indication of over-exploitation and can also cause problems for infrastructure such as aqueducts, flood-control projects, highways, bridges, and railways. If subsidence continues for too long, it can lead to irreversible collapse of the aquifer system, reducing its ability to recharge when water is available.
Subsidence As a Measure of Groundwater Depletion
In order to increase resilience and adapt to changes, water resource managers need to be able to detect new areas of subsidence and to monitor known areas of continuing subsidence. This will also give an indication of groundwater depletion over long periods. Currently this is done through periodic leveling surveys and monitoring of water wells, but owing to lack of funds and the difficultly of mandating measurements at private wells, the data are sparse in space and time.

Mapping and monitoring changes in land surface elevation with interferometric synthetic aperture radar (InSAR) may help fill in the gaps, both spatially and temporally. The ability to map surface deformation of a few mm monthly over large areas at resolutions of a few 10's of m has opened up new possibilities for remote monitoring of groundwater resources.
NISAR Mission: All-Weather Day and Night Imaging
The NASA-ISRO SAR (NISAR) Mission will acquire images of surface changes globally with millimeter accuracy and meter-scale resolution. It will capture images of the movements of the Earth over time and with sufficient detail to reveal what is happening below the surface. Rapid sampling over years to decades will allow for understanding groundwater dynamics. The detailed observations will reveal information about the migration of water and state of aquifers.
Managing Water Globally
NISAR offers the promise of extending these observations to regions of the world with no effective means to monitor the state of their groundwater. This would provide benefits to large segments of the global population dependent on groundwater to bridge gaps in surface and rain water supply. As Earth's climate changes, monitoring of this critical resource could help reduce conflicts over water.
Mapping Floods
In polarimetric mode, NISAR can also easily map flooded areas, even under vegetation canopies. Floods are important not only for their impact on society, but are significant means for redistribution of sediment on flood plains.

Subsidence Processes
FILE:files/nisar/NASA_ISRO_SAR_Mission_Water1.pdf
Water White Paper (PDF, 817 KB)