<h1>Evapotranspiration</h1>
<p>Understanding the way your plants function helps provide the right amount of water to ensure a healthy landscape and maximizes the efficiency of water applied to your landscape.&nbsp;</p>
<p>One way to do this is by using local weather conditions to help determine how much water your lawn and plants need to maintain healthy growing conditions.</p>
<h2>The Basics Of How Plants Function</h2>
<p><img alt="" height="230" src="/sites/default/files/images/diagram_watersmart_et.gif" style="float: right" width="200" /></p>
<p>Just as you release water vapor when you breathe, plants do too! It&rsquo;s called <strong>transpiration</strong>.&nbsp; When plants transpire faster than water is being replaced, they can wilt or die.&nbsp; Similarly, soils also lose moisture through <strong>evaporation</strong>.</p>
<p>Combine the two and you&rsquo;ve got <strong>Evapotranspiration</strong>, or ET, which is the combination of water lost from the soil through evaporation and from plants through transpiration.&nbsp; The amount of water lost through ET is equal to the amount of water that must be replaced to maintain healthy growing conditions.</p>
<p>Just remember:</p>
<ul>
	<li>ET values are calculated from local weather conditions to help you determine how much water is needed for your landscape.</li>
	<li>ET changes with local weather conditions.</li>
	<li>ET is affected by amount of sun, wind and air temperatures.</li>
	<li>ET varies for different types of plants.</li>
</ul>
<h2>So, Why Are We Talking About It?</h2>
<p>Here in the Portland metro area, water use can more than double in the summer months. Unfortunately, our usage increases at a time when there is less water available to us.</p>
<p>By making a few simple changes to your <a href="http://www.conserveh2o.org/measure-your-sprinklers-water-use-watering-gauges">watering routine</a>&nbsp;you can make a big difference for your plants and your pocketbook.</p>
<h2>How Are Evapotranspiration and The Weekly Watering Number Related?</h2>
<p>The Consortium contracts with a weather forecasting service to provide a free weather forecast and <a href="http://www.conserveh2o.org/weekly-watering-number">Weekly Watering Number</a> each Thursday.&nbsp; The Weekly Watering number is derived that week&rsquo;s evapotranspiration number.</p>
