Local Water Budgets: Components & Influences

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Water is a precious resource, and like all resources it can be budgeted. In this lesson, we'll talk about water budgets and see what factors impact their stability.

Water Budgets

Water is a precious resource. If you don't believe me, try living without it! We drink water, we use it to grow food, we use it to transport things, and we use it to power our homes and businesses. Water is important, and like all important things, we need to make sure we're using it appropriately. We don't want to overuse it, and we don't want to let it go to waste. So, just like we do with our money, we need to budget it. A water budget is a method for calculating the natural input and output in a water system. This system is meant only to examine the natural changes in water availability throughout a year and does not take into account human impact. If we think of the land like a bank for water, then the water budget helps us understand how much is being naturally deposited and withdrawn throughout the year. Then we can understand how much we have to work with.

Parts of the Water Budget

The water budget, like any budget, consists of various components. Some add water to the budget, and others remove it. Let's start with adding water. Most water in the budget comes from precipitation, including rain, snow, and even morning dew. Precipitation is like a deposit, adding available water to the budget. Of course, just like a paycheck can change due to available work, the amount of water being added to the budget changes by season. In wet seasons, precipitation is high. In the dry season, precipitation is low, and fewer deposits are made.

Precipitation is the main way water is added to the budget

Next, we need to look at water leaving the budget. Water can be naturally withdrawn through two primary systems. Evaporation refers to the process by which exposed surface water is turned into vapor in the air. Hot and dry climates will withdraw lots of water in this way. The other system is evapotranspiration. Evapotranspiration refers to water converted into vapor from either the land surface or from plants, which suck up water from the ground and lose some of it through the pores in their leaves. These are two different systems of withdrawing funds from the water budget, and each can change due to various factors. Evaporation is largely defined by climate. Evapotranspiration, however, is defined by the type of soil, types of plants, and amount of plants.

More water tends to evaporate from hot and dry climates

Runoff and Groundwater

Most of the water budget is determined by the direct deposits from precipitation and the direct withdrawals from evaporation and evapotranspiration. However, there are a few other factors to consider as well. First, surface runoff can either increase or decrease the water budget. This term describes the amount of water introduced or lost thanks to the slope, quality of soil, and gradient of the surface. Imagine, for example, a dry valley. It gets little precipitation, but it may still receive deposits to the water budget if it rains in the mountains. The hard soil and steep slope of the mountains bring water from the mountains to the valley. While the mountains loose more water this way, the valley gains it.

Under the right conditions, runoff can add a lot of water to the budget

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