The 4-inch Plant Available Water map is based on the 24-hour-averaged plant available water for the top 4 inches (10 cm) of soil under the existing vegetation at each Mesonet site for the previous day. Plant available water under other vegetation types may differ. Plant available water is the amount of water in the soil that is potentially available for plant uptake. Technically, it is calculated as the amount of soil water at matric potentials above -1500 kPa. The maximum possible plant available water varies between sites due to soil differences. Most plants experience water stress when less than 50% of the maximum plant available water remains in the active root zone. This map is updated once each day between 7 and 8 AM.