Why irrigate the desert? The question appears simple. Yet, the number of human and natural phenomenon that come together to reason moving water for growing food is impressive. There are three forces; plants, water and jobs that best summarize why we irrigate the desert.
First, what is a desert? The simple definition is a landscape or region that receives less than 10 in of precipitation per year. According to rainfall data from the California irrigation management system, my research site received 50 inches of rain during the last ten years. Compared to my hometown on the east coast; 5 inches per year is up to ten times less precipitation.
How are plants engineered to survive and thrive in the desert? Simply, sunlight fuels plant productivity. Let us compare the plants we use as crops to a factory where our major goal is productivity. The driver of the plant factory is photosynthesis and one way to measure the amount of sunlight to reach a plant leaf is solar radiation.
Using Direct Normal Irradiance (DNI), a solar engineer’s term for the amount of sunlight reach a given area, I illustrate my point. There is far more sunlight for plant growth at my research site compared to the entire northeast coast of the US. The scale is measure from red (7.0 kilowatts per sq. meter per day) to blue (2.0 kilowatts per sq. meter per day).
One more thing about plants that is they perform maintenance at night, which serves a plant well in the desert . The heat absorbed by the ground during the day escapes into the clear night. During the summer at my research site, the temperature drops to a cool 60 degrees F. Cool and dry summer nights allow plants to spend less energy to perform upkeep.
The end result of high sunlight days and cool summer nights is more sugars to sweeten fruit and to build other complex molecules. In California, there are many types of plants such as grapevines and trees that bear fruit like peaches, nectarines and oranges and dry fruit like almonds and pistachios. The high productivity and vast acreage of these crops allows growers to supply supermarkets from North America to Europe and Asia.
The critical player for farming places like my research site is water. The natural flow of water from the South San Joaquin Valley is north toward the the San Francisco Bay. The California Aqueduct moves water south toward Southern California and many farms are adjacent to it. The migration of water from north to south is generally against the precipitation gradient, there is more rain in Northern California and with the population gradient, there are more people in Southern California.
Water is a precious resource and no industry knows better than California agriculture. In response to the need to conserve water, irrigation technology has made substantial changes from flood irrigation to microjet sprinklers like the one above. Furthermore, a change in water delivery led to shift away from annual row crops like cotton to more permanent perennial crops like almond.
Finally in rural areas with desert, agriculture is a viable industry to create jobs and absorb labor. I bet if you ask U.S. representative Jim Costa, State Assemblyman Danny Gilmore or State Senator Dean Florez what drives the economy in their districts; they would say agriculture and the availability of water. Often agriculture may supply the only jobs in a community for general labor and management. The scenario appears clear that with limited water comes reduced production and without viable agriculture comes fewer jobs.
The next time you drive between Los Angeles and San Franicisco on Interstate 5 or you enjoy fresh fruit or nuts from California’s South San Joaquin Valley know you are a part of an irrigated desert landscape. The truth is no one really knows how long the desert can sustain agricultural production. But, right now it is an industry that works for you, for its communities and for a profit. Perhaps now the idea to irrigate the desert appears either more or less reasonable.